Thursday, 29 August 2013

PHP Database

With PHP, you can connect to and manipulate databases.

MySQL is the most popular database system used with PHP.

What is MySQL?

MySQL is a database system used on the web
MySQL is a database system that runs on a server
MySQL is ideal for both small and large applications
MySQL is very fast, reliable, and easy to use
MySQL supports standard SQL
MySQL compiles on a number of platforms
MySQL is free to download and use
MySQL is developed, distributed, and supported by Oracle Corporation
MySQL is named after co-founder Monty Widenius's daughter: My

The data in MySQL is stored in tables. A table is a collection of related data, and it consists of columns and rows.
Databases are useful when storing information categorically. A company may have a database with the following tables:

Employees
Products
Customers
Orders

PHP + MySQL

PHP combined with MySQL are cross-platform (you can develop in Windows and serve on a Unix platform)

Queries

A query is a question or a request.
We can query a database for specific information and have a recordset returned.
Look at the following query (using standard SQL):

SELECT LastName FROM Employees

The query above selects all the data in the "LastName" column from the "Employees" table.

Download MySQL Database

If you don't have a PHP server with a MySQL Database, you can download MySQL for free here: http://www.mysql.com

Facts About MySQL Database

One great thing about MySQL is that it can be scaled down to support embedded database applications. Maybe it is because of this many people think that MySQL can only handle small and medium-sized systems.
The truth is that MySQL is the de-facto standard database system for web sites with HUGE volumes of both data and end users (like Friendster, Yahoo, and Google).
Look at http://www.mysql.com/customers/ for an overview of companies using MySQL.

Use the PHP mysqli_connect() function to open a new connection to the MySQL server.

Open a Connection to the MySQL Server

Before we can access data in a database, we must open a connection to the MySQL server.
In PHP, this is done with the mysqli_connect() function.

Syntax

mysqli_connect(host,username,password,dbname);

Parameter	Description
host	Optional. Either a host name or an IP address
username	Optional. The MySQL user name
password	Optional. The password to log in with
dbname	Optional. The default database to be used when performing queries

Note: There are more available parameters, but the ones listed above are the most important.
In the following example we store the connection in a variable ($con) for later use in the script:

<?php
// Create connection
$con=mysqli_connect("example.com","peter","abc123","my_db");

// Check connection
if (mysqli_connect_errno($con))
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}
?>

Close a Connection

The connection will be closed automatically when the script ends. To close the connection before, use the mysqli_close() function:

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");

// Check connection
if (mysqli_connect_errno($con))
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

mysqli_close($con);
?>

A database holds one or more tables.

Create a Database

The CREATE DATABASE statement is used to create a database table in MySQL.
We must add the CREATE DATABASE statement to the mysqli_query() function to execute the command.
The following example creates a database named "my_db":

<?php
$con=mysqli_connect("example.com","peter","abc123");
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

// Create database
$sql="CREATE DATABASE my_db";
if (mysqli_query($con,$sql))
{
echo "Database my_db created successfully";
}
else
{
echo "Error creating database: " . mysqli_error($con);
}
?>

Create a Table

The CREATE TABLE statement is used to create a table in MySQL.
We must add the CREATE TABLE statement to the mysqli_query() function to execute the command.
The following example creates a table named "Persons", with three columns: "FirstName", "LastName" and "Age":

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

// Create table
$sql="CREATE TABLE Persons(FirstName CHAR(30),LastName CHAR(30),Age INT)";

// Execute query
if (mysqli_query($con,$sql))
{
echo "Table persons created successfully";
}
else
{
echo "Error creating table: " . mysqli_error($con);
}
?>

Note: When you create a field of type CHAR, you must specify the maximum length of the field, e.g. CHAR(50).
The data type specifies what type of data the column can hold. For a complete reference of all the data types available in MySQL, go to our complete Data Types reference.

Primary Keys and Auto Increment Fields

Each table in a database should have a primary key field.
A primary key is used to uniquely identify the rows in a table. Each primary key value must be unique within the table. Furthermore, the primary key field cannot be null because the database engine requires a value to locate the record.
The following example sets the PID field as the primary key field. The primary key field is often an ID number, and is often used with the AUTO_INCREMENT setting. AUTO_INCREMENT automatically increases the value of the field by 1 each time a new record is added. To ensure that the primary key field cannot be null, we must add the NOT NULL setting to the field:

$sql = "CREATE TABLE Persons
(
PID INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY(PID),
FirstName CHAR(15),
LastName CHAR(15),
Age INT
)";

The INSERT INTO statement is used to insert new records in a table.

Insert Data Into a Database Table

The INSERT INTO statement is used to add new records to a database table.

Syntax

It is possible to write the INSERT INTO statement in two forms.
The first form doesn't specify the column names where the data will be inserted, only their values:

INSERT INTO table_name
VALUES (value1, value2, value3,...)

The second form specifies both the column names and the values to be inserted:

INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...)

To learn more about SQL, please visit our SQL tutorial.To get PHP to execute the statements above we must use the mysqli_query() function. This function is used to send a query or command to a MySQL connection.

Example

In the previous chapter we created a table named "Persons", with three columns; "FirstName", "LastName" and "Age". We will use the same table in this example. The following example adds two new records to the "Persons" table:

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

mysqli_query($con,"INSERT INTO Persons (FirstName, LastName, Age)
VALUES ('Peter', 'Griffin',35)");

mysqli_query($con,"INSERT INTO Persons (FirstName, LastName, Age)
VALUES ('Glenn', 'Quagmire',33)");

mysqli_close($con);
?>

Insert Data From a Form Into a Database

Now we will create an HTML form that can be used to add new records to the "Persons" table.
Here is the HTML form:

<html>
<body>

<form action="insert.php" method="post">
Firstname: <input type="text" name="firstname">
Lastname: <input type="text" name="lastname">
Age: <input type="text" name="age">
<input type="submit">
</form>

</body>
</html>

When a user clicks the submit button in the HTML form, in the example above, the form data is sent to "insert.php".
The "insert.php" file connects to a database, and retrieves the values from the form with the PHP $_POST variables.
Then, the mysqli_query() function executes the INSERT INTO statement, and a new record will be added to the "Persons" table.
Here is the "insert.php" page:

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
  {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$sql="INSERT INTO Persons (FirstName, LastName, Age)
VALUES
('$_POST[firstname]','$_POST[lastname]','$_POST[age]')";

if (!mysqli_query($con,$sql))
  {
  die('Error: ' . mysqli_error($con));
  }
echo "1 record added";

mysqli_close($con);
?>

--------------------------

The SELECT statement is used to select data from a database.

Select Data From a Database Table

The SELECT statement is used to select data from a database.

Syntax

SELECT column_name(s)
FROM table_name

To learn more about SQL, please visit our SQL tutorial.
To get PHP to execute the statement above we must use the mysqli_query() function. This function is used to send a query or command to a MySQL connection.

Example

The following example selects all the data stored in the "Persons" table (The * character selects all the data in the table):

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
  {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$result = mysqli_query($con,"SELECT * FROM Persons");

while($row = mysqli_fetch_array($result))
  {
  echo $row['FirstName'] . " " . $row['LastName'];
  echo "<br>";
  }

mysqli_close($con);
?>

The example above stores the data returned by the mysqli_query() function in the $result variable.
Next, we use the mysqli_fetch_array() function to return the first row from the recordset as an array. Each call to mysqli_fetch_array() returns the next row in the recordset. The while loop loops through all the records in the recordset. To print the value of each row, we use the PHP $row variable ($row['FirstName'] and $row['LastName']).
The output of the code above will be:

Peter Griffin
Glenn Quagmire

Display the Result in an HTML Table

The following example selects the same data as the example above, but will display the data in an HTML table:

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
  {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$result = mysqli_query($con,"SELECT * FROM Persons");

echo "<table border='1'>
<tr>
<th>Firstname</th>
<th>Lastname</th>
</tr>";

while($row = mysqli_fetch_array($result))
  {
  echo "<tr>";
  echo "<td>" . $row['FirstName'] . "</td>";
  echo "<td>" . $row['LastName'] . "</td>";
  echo "</tr>";
  }
echo "</table>";

mysqli_close($con);
?>

The output of the code above will be:

Firstname	Lastname
Glenn	Quagmire
Peter	Griffin

-----------------------------

The WHERE clause is used to filter records.

The WHERE clause

The WHERE clause is used to extract only those records that fulfill a specified criterion.

Syntax

SELECT column_name(s)
FROM table_name
WHERE column_name operator value

Example

The following example selects all rows from the "Persons" table where "FirstName='Peter'":

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
  {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$result = mysqli_query($con,"SELECT * FROM Persons
WHERE FirstName='Peter'");

while($row = mysqli_fetch_array($result))
  {
  echo $row['FirstName'] . " " . $row['LastName'];
  echo "<br>";
  }
?>

The output of the code above will be:

Peter Griffin

---------------------------

The ORDER BY keyword is used to sort the data in a recordset.

The ORDER BY Keyword

The ORDER BY keyword is used to sort the data in a recordset.
The ORDER BY keyword sort the records in ascending order by default.
If you want to sort the records in a descending order, you can use the DESC keyword.

Syntax

SELECT column_name(s)
FROM table_name
ORDER BY column_name(s) ASC|DESC

To learn more about SQL, please visit our SQL tutorial.

Example

The following example selects all the data stored in the "Persons" table, and sorts the result by the "Age" column:

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
  {
echo "Failed to connect to MySQL: " . mysqli_connect_error();
  }

$result = mysqli_query($con,"SELECT * FROM Persons ORDER BY age");

while($row = mysqli_fetch_array($result))
  {
  echo $row['FirstName'];
  echo " " . $row['LastName'];
  echo " " . $row['Age'];
  echo "<br>";
  }

mysqli_close($con);
?>

The output of the code above will be:

Glenn Quagmire 33
Peter Griffin 35

Order by Two Columns

It is also possible to order by more than one column. When ordering by more than one column, the second column is only used if the values in the first column are equal:

SELECT column_name(s)
FROM table_name
ORDER BY column1, column2

-------------------------

The UPDATE statement is used to modify data in a table.

Update Data In a Database

The UPDATE statement is used to update existing records in a table.

Syntax

UPDATE table_name
SET column1=value, column2=value2,...
WHERE some_column=some_value

Note: Notice the WHERE clause in the UPDATE syntax. The WHERE clause specifies which record or records that should be updated. If you omit the WHERE clause, all records will be updated!To learn more about SQL, please visit our SQL tutorial.
To get PHP to execute the statement above we must use the mysqli_query() function. This function is used to send a query or command to a MySQL connection.

Example

Earlier in the tutorial we created a table named "Persons". Here is how it looks:

FirstName	LastName	Age
Peter	Griffin	35
Glenn	Quagmire	33

The following example updates some data in the "Persons" table:

<?php
$con=mysqli_connect("example.com","peter","abc123","my_db");
// Check connection
if (mysqli_connect_errno())
{
echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

mysqli_query($con,"UPDATE Persons SET Age=36
WHERE FirstName='Peter' AND LastName='Griffin'");

mysqli_close($con);
?>

After the update, the "Persons" table will look like this:

FirstName	LastName	Age
Peter	Griffin	36
Glenn	Quagmire	33

---------------------

The DELETE statement is used to delete records in a table.

Delete Data In a Database

The DELETE FROM statement is used to delete records from a database table.

Syntax

DELETE FROM table_name
WHERE some_column = some_value

Note: Notice the WHERE clause in the DELETE syntax. The WHERE clause specifies which record or records that should be deleted. If you omit the WHERE clause, all records will be deleted!To learn more about SQL, please visit our SQL tutorial.
To get PHP to execute the statement above we must use the mysqli_query() function. This function is used to send a query or command to a MySQL connection.

Example

Look at the following "Persons" table:

FirstName	LastName	Age
Peter	Griffin	35
Glenn	Quagmire	33

The following example deletes all the records in the "Persons" table where LastName='Griffin':

After the deletion, the table will look like this:

FirstName	LastName	Age
Glenn	Quagmire	33

------------------------

ODBC is an Application Programming Interface (API) that allows you to connect to a data source (e.g. an MS Access database).

Create an ODBC Connection

With an ODBC connection, you can connect to any database, on any computer in your network, as long as an ODBC connection is available.
Here is how to create an ODBC connection to a MS Access Database:

Open the Administrative Tools icon in your Control Panel.
Double-click on the Data Sources (ODBC) icon inside.
Choose the System DSN tab.
Click on Add in the System DSN tab.
Select the Microsoft Access Driver. Click Finish.
In the next screen, click Select to locate the database.
Give the database a Data Source Name (DSN).
Click OK.

Note that this configuration has to be done on the computer where your web site is located. If you are running Internet Information Server (IIS) on your own computer, the instructions above will work, but if your web site is located on a remote server, you have to have physical access to that server, or ask your web host to to set up a DSN for you to use.

Connecting to an ODBC

The odbc_connect() function is used to connect to an ODBC data source. The function takes four parameters: the data source name, username, password, and an optional cursor type.
The odbc_exec() function is used to execute an SQL statement.

Example

The following example creates a connection to a DSN called northwind, with no username and no password. It then creates an SQL and executes it:

$conn=odbc_connect('northwind','','');
$sql="SELECT * FROM customers";
$rs=odbc_exec($conn,$sql);

Retrieving Records

The odbc_fetch_row() function is used to return records from the result-set. This function returns true if it is able to return rows, otherwise false.
The function takes two parameters: the ODBC result identifier and an optional row number:

odbc_fetch_row($rs)

Retrieving Fields from a Record

The odbc_result() function is used to read fields from a record. This function takes two parameters: the ODBC result identifier and a field number or name.
The code line below returns the value of the first field from the record:

$compname=odbc_result($rs,1);

The code line below returns the value of a field called "CompanyName":

$compname=odbc_result($rs,"CompanyName");

Closing an ODBC Connection

The odbc_close() function is used to close an ODBC connection.

odbc_close($conn);

An ODBC Example

The following example shows how to first create a database connection, then a result-set, and then display the data in an HTML table.

<html>
<body>

<?php
$conn=odbc_connect('northwind','','');
if (!$conn)
  {exit("Connection Failed: " . $conn);}
$sql="SELECT * FROM customers";
$rs=odbc_exec($conn,$sql);
if (!$rs)
  {exit("Error in SQL");}
echo "<table><tr>";
echo "<th>Companyname</th>";
echo "<th>Contactname</th></tr>";
while (odbc_fetch_row($rs))
  {
  $compname=odbc_result($rs,"CompanyName");
  $conname=odbc_result($rs,"ContactName");
  echo "<tr><td>$compname</td>";
  echo "<td>$conname</td></tr>";
  }
odbc_close($conn);
echo "</table>";
?>

</body>
</html>

PHP Advanced

PHP Multidimensional Arrays

An array can also contain another array as a value, which in turn can hold other arrays as well. In such a way we can create two- or three-dimensional arrays:

Example

<?php
// A two-dimensional array:
$cars = array
(
array("Volvo",100,96),
array("BMW",60,59),
array("Toyota",110,100)
);
?>

PHP - Multidimensional Arrays

A multidimensional array is an array containing one or more arrays.
In a multidimensional array, each element in the main array can also be an array. And each element in the sub-array can be an array, and so on.

Example

In this example we create a multidimensional array, with automatically assigned ID keys:

$families = array
  (
  "Griffin"=>array
  (
  "Peter",
  "Lois",
  "Megan"
  ),
  "Quagmire"=>array
  (
  "Glenn"
  ),
  "Brown"=>array
  (
  "Cleveland",
  "Loretta",
  "Junior"
  )
  );

The array above would look like this if written to the output:

Array
(
[Griffin] => Array
  (
  [0] => Peter
  [1] => Lois
  [2] => Megan
  )
[Quagmire] => Array
  (
  [0] => Glenn
  )
[Brown] => Array
  (
  [0] => Cleveland
  [1] => Loretta
  [2] => Junior
  )
)

Example 2

Lets try displaying a single value from the array above:

echo "Is " . $families['Griffin'][2] .
" a part of the Griffin family?";

The code above will output:

Is Megan a part of the Griffin family?

-------------------------------

The PHP date() function is used to format a time and/or date.

The PHP Date() Function

The PHP date() function formats a timestamp to a more readable date and time.
Tip

A timestamp is a sequence of characters, denoting the date and/or time at which a certain event occurred.

Syntax

date(format,timestamp)

Parameter	Description
format	Required. Specifies the format of the timestamp
timestamp	Optional. Specifies a timestamp. Default is the current date and time

PHP Date() - Format the Date

The required format parameter in the date() function specifies how to format the date/time.
Here are some characters that can be used:

d - Represents the day of the month (01 to 31)
m - Represents a month (01 to 12)
Y - Represents a year (in four digits)

A list of all the characters that can be used in the format parameter, can be found in our PHP Date reference, date() function.
Other characters, like"/", ".", or "-" can also be inserted between the letters to add additional formatting:

<?php
echo date("Y/m/d") . "<br>";
echo date("Y.m.d") . "<br>";
echo date("Y-m-d");
?>

The output of the code above could be something like this:

2009/05/11
2009.05.11
2009-05-11

PHP Date() - Adding a Timestamp

The optional timestamp parameter in the date() function specifies a timestamp. If you do not specify a timestamp, the current date and time will be used.
The mktime() function returns the Unix timestamp for a date.
The Unix timestamp contains the number of seconds between the Unix Epoch (January 1 1970 00:00:00 GMT) and the time specified.

Syntax for mktime()

mktime(hour,minute,second,month,day,year,is_dst)

To go one day in the future we simply add one to the day argument of mktime():

<?php
$tomorrow = mktime(0,0,0,date("m"),date("d")+1,date("Y"));
echo "Tomorrow is ".date("Y/m/d", $tomorrow);
?>

The output of the code above could be something like this:

Tomorrow is 2009/05/12

PHP include and require Statements

In PHP, you can insert the content of one PHP file into another PHP file before the server executes it.
The include and require statements are used to insert useful codes written in other files, in the flow of execution.
Include and require are identical, except upon failure:

require will produce a fatal error (E_COMPILE_ERROR) and stop the script
include will only produce a warning (E_WARNING) and the script will continue

So, if you want the execution to go on and show users the output, even if the include file is missing, use include. Otherwise, in case of FrameWork, CMS or a complex PHP application coding, always use require to include a key file to the flow of execution. This will help avoid compromising your application's security and integrity, just in-case one key file is accidentally missing.
Including files saves a lot of work. This means that you can create a standard header, footer, or menu file for all your web pages. Then, when the header needs to be updated, you can only update the header include file.

Syntax

include 'filename';

or

require 'filename';

PHP include and require Statement

Basic Example

Assume that you have a standard header file, called "header.php". To include the header file in a page, use include/require:

<html>
<body>

<?php include 'header.php'; ?>
<h1>Welcome to my home page!</h1>
<p>Some text.</p>

</body>
</html>

Example 2

Assume we have a standard menu file that should be used on all pages.
"menu.php":

echo '<a href="/default.php">Home</a>
<a href="/tutorials.php">Tutorials</a>
<a href="/references.php">References</a>
<a href="/examples.php">Examples</a>
<a href="/about.php">About Us</a>
<a href="/contact.php">Contact Us</a>';

All pages in the Web site should include this menu file. Here is how it can be done:

<html>
<body>

<div class="leftmenu">
<?php include 'menu.php'; ?>
</div>

<h1>Welcome to my home page.</h1>
<p>Some text.</p>

</body>
</html>

Example 3

Assume we have an include file with some variables defined ("vars.php"):

<?php
$color='red';
$car='BMW';
?>

Then the variables can be used in the calling file:

<html>
<body>

<h1>Welcome to my home page.</h1>
<?php include 'vars.php';
echo "I have a $color $car"; // I have a red BMW
?>

</body>
</html>

--------------------

The fopen() function is used to open files in PHP.

Opening a File

The fopen() function is used to open files in PHP.
The first parameter of this function contains the name of the file to be opened and the second parameter specifies in which mode the file should be opened:

The file may be opened in one of the following modes:

Modes	Description
r	Read only. Starts at the beginning of the file
r+	Read/Write. Starts at the beginning of the file
w	Write only. Opens and clears the contents of file; or creates a new file if it doesn't exist
w+	Read/Write. Opens and clears the contents of file; or creates a new file if it doesn't exist
a	Append. Opens and writes to the end of the file or creates a new file if it doesn't exist
a+	Read/Append. Preserves file content by writing to the end of the file
x	Write only. Creates a new file. Returns FALSE and an error if file already exists
x+	Read/Write. Creates a new file. Returns FALSE and an error if file already exists

Note: If the fopen() function is unable to open the specified file, it returns 0 (false).

Example

The following example generates a message if the fopen() function is unable to open the specified file:

Closing a File

The fclose() function is used to close an open file:

<?php
$file = fopen("test.txt","r");

//some code to be executed

fclose($file);
?>

Check End-of-file

The feof() function checks if the "end-of-file" (EOF) has been reached.

The feof() function is useful for looping through data of unknown length.
Note: You cannot read from files opened in w, a, and x mode!

if (feof($file)) echo "End of file";

Reading a File Line by Line

The fgets() function is used to read a single line from a file.
Note: After a call to this function the file pointer has moved to the next line.

Example

The example below reads a file line by line, until the end of file is reached:

<?php
$file = fopen("welcome.txt", "r") or exit("Unable to open file!");
//Output a line of the file until the end is reached
while(!feof($file))
  {
  echo fgets($file). "<br>";
  }
fclose($file);
?>

Reading a File Character by Character

The fgetc() function is used to read a single character from a file.
Note: After a call to this function the file pointer moves to the next character.

Example

The example below reads a file character by character, until the end of file is reached:

<?php
$file=fopen("welcome.txt","r") or exit("Unable to open file!");
while (!feof($file))
  {
  echo fgetc($file);
  }
fclose($file);
?>

With PHP, it is possible to upload files to the server.

Create an Upload-File Form

To allow users to upload files from a form can be very useful.
Look at the following HTML form for uploading files:

<html>
<body>

<form action="upload_file.php" method="post"
enctype="multipart/form-data">
<label for="file">Filename:</label>
<input type="file" name="file" id="file"><br>
<input type="submit" name="submit" value="Submit">
</form>

</body>
</html>

Notice the following about the HTML form above:

The enctype attribute of the <form> tag specifies which content-type to use when submitting the form. "multipart/form-data" is used when a form requires binary data, like the contents of a file, to be uploaded
The type="file" attribute of the <input> tag specifies that the input should be processed as a file. For example, when viewed in a browser, there will be a browse-button next to the input field

Note: Allowing users to upload files is a big security risk. Only permit trusted users to perform file uploads.

Create The Upload Script

The "upload_file.php" file contains the code for uploading a file:

<?php
if ($_FILES["file"]["error"] > 0)
  {
  echo "Error: " . $_FILES["file"]["error"] . "<br>";
  }
else
  {
  echo "Upload: " . $_FILES["file"]["name"] . "<br>";
  echo "Type: " . $_FILES["file"]["type"] . "<br>";
  echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br>";
  echo "Stored in: " . $_FILES["file"]["tmp_name"];
  }
?>

By using the global PHP $_FILES array you can upload files from a client computer to the remote server.
The first parameter is the form's input name and the second index can be either "name", "type", "size", "tmp_name" or "error". Like this:

$_FILES["file"]["name"] - the name of the uploaded file
$_FILES["file"]["type"] - the type of the uploaded file
$_FILES["file"]["size"] - the size in bytes of the uploaded file
$_FILES["file"]["tmp_name"] - the name of the temporary copy of the file stored on the server
$_FILES["file"]["error"] - the error code resulting from the file upload

This is a very simple way of uploading files. For security reasons, you should add restrictions on what the user is allowed to upload.

Restrictions on Upload

In this script we add some restrictions to the file upload. The user may upload .gif, .jpeg, and .png files; and the file size must be under 20 kB:

<?php
$allowedExts = array("gif", "jpeg", "jpg", "png");
$temp = explode(".", $_FILES["file"]["name"]);
$extension = end($temp);
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/jpg")
|| ($_FILES["file"]["type"] == "image/pjpeg")
|| ($_FILES["file"]["type"] == "image/x-png")
|| ($_FILES["file"]["type"] == "image/png"))
&& ($_FILES["file"]["size"] < 20000)
&& in_array($extension, $allowedExts))
  {
  if ($_FILES["file"]["error"] > 0)
    {
    echo "Error: " . $_FILES["file"]["error"] . "<br>";
    }
  else
    {
    echo "Upload: " . $_FILES["file"]["name"] . "<br>";
    echo "Type: " . $_FILES["file"]["type"] . "<br>";
    echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br>";
    echo "Stored in: " . $_FILES["file"]["tmp_name"];
    }
  }
else
  {
  echo "Invalid file";
  }
?>

Saving the Uploaded File

The examples above create a temporary copy of the uploaded files in the PHP temp folder on the server.
The temporary copied files disappears when the script ends. To store the uploaded file we need to copy it to a different location:

<?php
$allowedExts = array("gif", "jpeg", "jpg", "png");
$temp = explode(".", $_FILES["file"]["name"]);
$extension = end($temp);
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/jpg")
|| ($_FILES["file"]["type"] == "image/pjpeg")
|| ($_FILES["file"]["type"] == "image/x-png")
|| ($_FILES["file"]["type"] == "image/png"))
&& ($_FILES["file"]["size"] < 20000)
&& in_array($extension, $allowedExts))
  {
  if ($_FILES["file"]["error"] > 0)
    {
    echo "Return Code: " . $_FILES["file"]["error"] . "<br>";
    }
  else
    {
    echo "Upload: " . $_FILES["file"]["name"] . "<br>";
    echo "Type: " . $_FILES["file"]["type"] . "<br>";
    echo "Size: " . ($_FILES["file"]["size"] / 1024) . " kB<br>";
    echo "Temp file: " . $_FILES["file"]["tmp_name"] . "<br>";

    if (file_exists("upload/" . $_FILES["file"]["name"]))
      {
      echo $_FILES["file"]["name"] . " already exists. ";
      }
    else
      {
      move_uploaded_file($_FILES["file"]["tmp_name"],
      "upload/" . $_FILES["file"]["name"]);
      echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
      }
    }
  }
else
  {
  echo "Invalid file";
  }
?>

The script above checks if the file already exists, if it does not, it copies the file to a folder called "upload".

A cookie is often used to identify a user.

What is a Cookie?

A cookie is often used to identify a user. A cookie is a small file that the server embeds on the user's computer. Each time the same computer requests a page with a browser, it will send the cookie too. With PHP, you can both create and retrieve cookie values.

How to Create a Cookie?

The setcookie() function is used to set a cookie.
Note: The setcookie() function must appear BEFORE the <html> tag.

Syntax

setcookie(name, value, expire, path, domain);

Example 1

In the example below, we will create a cookie named "user" and assign the value "Alex Porter" to it. We also specify that the cookie should expire after one hour:

<?php
setcookie("user", "Alex Porter", time()+3600);
?>

<html>
.....

Note: The value of the cookie is automatically URLencoded when sending the cookie, and automatically decoded when received (to prevent URLencoding, use setrawcookie() instead).

Example 2

You can also set the expiration time of the cookie in another way. It may be easier than using seconds.

<?php
$expire=time()+60*60*24*30;
setcookie("user", "Alex Porter", $expire);
?>

<html>
.....

In the example above the expiration time is set to a month (60 sec * 60 min * 24 hours * 30 days).

How to Retrieve a Cookie Value?

The PHP $_COOKIE variable is used to retrieve a cookie value.

In the example below, we retrieve the value of the cookie named "user" and display it on a page:

<?php
// Print a cookie
echo $_COOKIE["user"];

// A way to view all cookies
print_r($_COOKIE);
?>

In the following example we use the isset() function to find out if a cookie has been set:

<html>
<body>

<?php
if (isset($_COOKIE["user"]))
echo "Welcome " . $_COOKIE["user"] . "!<br>";
else
echo "Welcome guest!<br>";
?>

</body>
</html>

How to Delete a Cookie?

When deleting a cookie you should assure that the expiration date is in the past.
Delete example:

<?php
// set the expiration date to one hour ago
setcookie("user", "", time()-3600);
?>

What if a Browser Does NOT Support Cookies?

If your application deals with browsers that do not support cookies, you will have to use other methods to pass information from one page to another in your application. One method is to pass the data through forms (forms and user input are described earlier in this tutorial).
The form below passes the user input to "welcome.php" when the user clicks on the "Submit" button:

Retrieve the values in the "welcome.php" file like this:

<html>
<body>

Welcome <?php echo $_POST["name"]; ?>.<br>
You are <?php echo $_POST["age"]; ?> years old.

</body>
</html>

A PHP session variable is used to store information about, or change settings for a user session. Session variables hold information about one single user, and are available to all pages in one application.

PHP Session Variables

When you are working with an application, you open it, do some changes and then you close it. This is much like a Session. The computer knows who you are. It knows when you start the application and when you end. But on the internet there is one problem: the web server does not know who you are and what you do because the HTTP address doesn't maintain state.
A PHP session solves this problem by allowing you to store user information on the server for later use (i.e. username, shopping items, etc). However, session information is temporary and will be deleted after the user has left the website. If you need a permanent storage you may want to store the data in a database.
Sessions work by creating a unique id (UID) for each visitor and store variables based on this UID. The UID is either stored in a cookie or is propagated in the URL.

Starting a PHP Session

Before you can store user information in your PHP session, you must first start up the session.
Note: The session_start() function must appear BEFORE the <html> tag:

<?php session_start(); ?>

<html>
<body>

</body>
</html>

The code above will register the user's session with the server, allow you to start saving user information, and assign a UID for that user's session.

Storing a Session Variable

The correct way to store and retrieve session variables is to use the PHP $_SESSION variable:

<?php
session_start();
// store session data
$_SESSION['views']=1;
?>

<html>
<body>

<?php
//retrieve session data
echo "Pageviews=". $_SESSION['views'];
?>

</body>
</html>

Output:

Pageviews=1

In the example below, we create a simple page-views counter. The isset() function checks if the "views" variable has already been set. If "views" has been set, we can increment our counter. If "views" doesn't exist, we create a "views" variable, and set it to 1:

<?php
session_start();

if(isset($_SESSION['views']))
$_SESSION['views']=$_SESSION['views']+1;
else
$_SESSION['views']=1;
echo "Views=". $_SESSION['views'];
?>

Destroying a Session

If you wish to delete some session data, you can use the unset() or the session_destroy() function.
The unset() function is used to free the specified session variable:

<?php
session_start();
if(isset($_SESSION['views']))
unset($_SESSION['views']);
?>

You can also completely destroy the session by calling the session_destroy() function:

<?php
session_destroy();
?>

Note: session_destroy() will reset your session and you will lose all your stored session data.

---------------------

PHP allows you to send e-mails directly from a script.

The PHP mail() Function

The PHP mail() function is used to send emails from inside a script.
Syntax

mail(to,subject,message,headers,parameters)

Parameter	Description
to	Required. Specifies the receiver / receivers of the email
subject	Required. Specifies the subject of the email. Note: This parameter cannot contain any newline characters
message	Required. Defines the message to be sent. Each line should be separated with a LF (\n). Lines should not exceed 70 characters
headers	Optional. Specifies additional headers, like From, Cc, and Bcc. The additional headers should be separated with a CRLF (\r\n)
parameters	Optional. Specifies an additional parameter to the sendmail program

Note: For the mail functions to be available, PHP requires an installed and working email system. The program to be used is defined by the configuration settings in the php.ini file. Read more in our PHP Mail reference.

PHP Simple E-Mail

The simplest way to send an email with PHP is to send a text email.
In the example below we first declare the variables ($to, $subject, $message, $from, $headers), then we use the variables in the mail() function to send an e-mail:

<?php
$to = "someone@example.com";
$subject = "Test mail";
$message = "Hello! This is a simple email message.";
$from = "someonelse@example.com";
$headers = "From:" . $from;
mail($to,$subject,$message,$headers);
echo "Mail Sent.";
?>

PHP Mail Form

With PHP, you can create a feedback-form on your website. The example below sends a text message to a specified e-mail address:

<html>
<body>

<?php
if (isset($_REQUEST['email']))
//if "email" is filled out, send email
  {
  //send email
  $email = $_REQUEST['email'] ;
  $subject = $_REQUEST['subject'] ;
  $message = $_REQUEST['message'] ;
  mail("someone@example.com", $subject,
  $message, "From:" . $email);
  echo "Thank you for using our mail form";
  }
else
//if "email" is not filled out, display the form
  {
  echo "<form method='post' action='mailform.php'>
  Email: <input name='email' type='text'><br>
  Subject: <input name='subject' type='text'><br>
  Message:<br>
  <textarea name='message' rows='15' cols='40'>
  </textarea><br>
  <input type='submit'>
  </form>";
  }
?>

</body>
</html>

This is how the example above works:

First, check if the email input field is filled out
If it is not set (like when the page is first visited); output the HTML form
If it is set (after the form is filled out); send the email from the form
When submit is pressed after the form is filled out, the page reloads, sees that the email input is set, and sends the email

Note: This is the simplest way to send e-mail, but it is not secure. In the next chapter of this tutorial you can read more about vulnerabilities in e-mail scripts, and how to validate user input to make it more secure.

There is a weakness in the PHP e-mail script in the previous chapter.

PHP E-mail Injections

First, look at the PHP code from the previous chapter:

<html>
<body>

<?php
if (isset($_REQUEST['email']))
//if "email" is filled out, send email
  {
  //send email
  $email = $_REQUEST['email'] ;
  $subject = $_REQUEST['subject'] ;
  $message = $_REQUEST['message'] ;
  mail("someone@example.com", "Subject: $subject",
  $message, "From: $email" );
  echo "Thank you for using our mail form";
  }
else
//if "email" is not filled out, display the form
  {
  echo "<form method='post' action='mailform.php'>
  Email: <input name='email' type='text'><br>
  Subject: <input name='subject' type='text'><br>
  Message:<br>
  <textarea name='message' rows='15' cols='40'>
  </textarea><br>
  <input type='submit'>
  </form>";
  }
?>

</body>
</html>

The problem with the code above is that unauthorized users can insert data into the mail headers via the input form.
What happens if the user adds the following text to the email input field in the form?

someone@example.com%0ACc:person2@example.com
%0ABcc:person3@example.com,person3@example.com,
anotherperson4@example.com,person5@example.com
%0ABTo:person6@example.com

The mail() function puts the text above into the mail headers as usual, and now the header has an extra Cc:, Bcc:, and To: field. When the user clicks the submit button, the e-mail will be sent to all of the addresses above!

PHP Stopping E-mail Injections

The best way to stop e-mail injections is to validate the input.
The code below is the same as in the previous chapter, but now we have added an input validator that checks the email field in the form:

<html>
<body>
<?php
function spamcheck($field)
  {
  //filter_var() sanitizes the e-mail
  //address using FILTER_SANITIZE_EMAIL
  $field=filter_var($field, FILTER_SANITIZE_EMAIL);

  //filter_var() validates the e-mail
  //address using FILTER_VALIDATE_EMAIL
  if(filter_var($field, FILTER_VALIDATE_EMAIL))
    {
    return TRUE;
    }
  else
    {
    return FALSE;
    }
  }

if (isset($_REQUEST['email']))
  {//if "email" is filled out, proceed

  //check if the email address is invalid
  $mailcheck = spamcheck($_REQUEST['email']);
  if ($mailcheck==FALSE)
    {
    echo "Invalid input";
    }
  else
    {//send email
    $email = $_REQUEST['email'] ;
    $subject = $_REQUEST['subject'] ;
    $message = $_REQUEST['message'] ;
    mail("someone@example.com", "Subject: $subject",
    $message, "From: $email" );
    echo "Thank you for using our mail form";
    }
  }
else
  {//if "email" is not filled out, display the form
  echo "<form method='post' action='mailform.php'>
  Email: <input name='email' type='text'><br>
  Subject: <input name='subject' type='text'><br>
  Message:<br>
  <textarea name='message' rows='15' cols='40'>
  </textarea><br>
  <input type='submit'>
  </form>";
  }
?>

</body>
</html>

In the code above we use PHP filters to validate input:

The FILTER_SANITIZE_EMAIL filter removes all illegal e-mail characters from a string
The FILTER_VALIDATE_EMAIL filter validates value as an e-mail address

The default error handling in PHP is very simple. An error message with filename, line number and a message describing the error is sent to the browser.

PHP Error Handling

When creating scripts and web applications, error handling is an important part. If your code lacks error checking code, your program may look very unprofessional and you may be open to security risks.
This tutorial contains some of the most common error checking methods in PHP.
We will show different error handling methods:

Simple "die()" statements
Custom errors and error triggers
Error reporting

Basic Error Handling: Using the die() function

The first example shows a simple script that opens a text file:

<?php
$file=fopen("welcome.txt","r");
?>

If the file does not exist you might get an error like this:

Warning: fopen(welcome.txt) [function.fopen]: failed to open stream:
No such file or directory in C:\webfolder\test.php on line 2

To prevent the user from getting an error message like the one above, we test whether the file exist before we try to access it:

<?php
if(!file_exists("welcome.txt"))
  {
  die("File not found");
  }
else
  {
  $file=fopen("welcome.txt","r");
  }
?>

Now if the file does not exist you get an error like this:

File not found

The code above is more efficient than the earlier code, because it uses a simple error handling mechanism to stop the script after the error.
However, simply stopping the script is not always the right way to go. Let's take a look at alternative PHP functions for handling errors.

Creating a Custom Error Handler

Creating a custom error handler is quite simple. We simply create a special function that can be called when an error occurs in PHP.
This function must be able to handle a minimum of two parameters (error level and error message) but can accept up to five parameters (optionally: file, line-number, and the error context):

Syntax

error_function(error_level,error_message,
error_file,error_line,error_context)

Parameter	Description
error_level	Required. Specifies the error report level for the user-defined error. Must be a value number. See table below for possible error report levels
error_message	Required. Specifies the error message for the user-defined error
error_file	Optional. Specifies the filename in which the error occurred
error_line	Optional. Specifies the line number in which the error occurred
error_context	Optional. Specifies an array containing every variable, and their values, in use when the error occurred

Error Report levels

These error report levels are the different types of error the user-defined error handler can be used for:

Value	Constant	Description
2	E_WARNING	Non-fatal run-time errors. Execution of the script is not halted
8	E_NOTICE	Run-time notices. The script found something that might be an error, but could also happen when running a script normally
256	E_USER_ERROR	Fatal user-generated error. This is like an E_ERROR set by the programmer using the PHP function trigger_error()
512	E_USER_WARNING	Non-fatal user-generated warning. This is like an E_WARNING set by the programmer using the PHP function trigger_error()
1024	E_USER_NOTICE	User-generated notice. This is like an E_NOTICE set by the programmer using the PHP function trigger_error()
4096	E_RECOVERABLE_ERROR	Catchable fatal error. This is like an E_ERROR but can be caught by a user defined handle (see also set_error_handler())
8191	E_ALL	All errors and warnings (E_STRICT became a part of E_ALL in PHP 5.4)

Now lets create a function to handle errors:

function customError($errno, $errstr)
  {
  echo "<b>Error:</b> [$errno] $errstr<br>";
  echo "Ending Script";
  die();
  }

The code above is a simple error handling function. When it is triggered, it gets the error level and an error message. It then outputs the error level and message and terminates the script.
Now that we have created an error handling function we need to decide when it should be triggered.

Set Error Handler

The default error handler for PHP is the built in error handler. We are going to make the function above the default error handler for the duration of the script.
It is possible to change the error handler to apply for only some errors, that way the script can handle different errors in different ways. However, in this example we are going to use our custom error handler for all errors:

set_error_handler("customError");

Since we want our custom function to handle all errors, the set_error_handler() only needed one parameter, a second parameter could be added to specify an error level.

Example

Testing the error handler by trying to output variable that does not exist:

<?php
//error handler function
function customError($errno, $errstr)
  {
  echo "<b>Error:</b> [$errno] $errstr";
  }

//set error handler
set_error_handler("customError");

//trigger error
echo($test);
?>

The output of the code above should be something like this:

Error: [8] Undefined variable: test

Trigger an Error

In a script where users can input data it is useful to trigger errors when an illegal input occurs. In PHP, this is done by the trigger_error() function.

Example

In this example an error occurs if the "test" variable is bigger than "1":

<?php
$test=2;
if ($test>1)
{
trigger_error("Value must be 1 or below");
}
?>

The output of the code above should be something like this:

Notice: Value must be 1 or below
in C:\webfolder\test.php on line 6

An error can be triggered anywhere you wish in a script, and by adding a second parameter, you can specify what error level is triggered.
Possible error types:

E_USER_ERROR - Fatal user-generated run-time error. Errors that can not be recovered from. Execution of the script is halted
E_USER_WARNING - Non-fatal user-generated run-time warning. Execution of the script is not halted
E_USER_NOTICE - Default. User-generated run-time notice. The script found something that might be an error, but could also happen when running a script normally

Example

In this example an E_USER_WARNING occurs if the "test" variable is bigger than "1". If an E_USER_WARNING occurs we will use our custom error handler and end the script:

<?php
//error handler function
function customError($errno, $errstr)
  {
  echo "<b>Error:</b> [$errno] $errstr<br>";
  echo "Ending Script";
  die();
  }

//set error handler
set_error_handler("customError",E_USER_WARNING);

//trigger error
$test=2;
if ($test>1)
  {
  trigger_error("Value must be 1 or below",E_USER_WARNING);
  }
?>

The output of the code above should be something like this:

Error: [512] Value must be 1 or below
Ending Script

Now that we have learned to create our own errors and how to trigger them, lets take a look at error logging.

Error Logging

By default, PHP sends an error log to the server's logging system or a file, depending on how the error_log configuration is set in the php.ini file. By using the error_log() function you can send error logs to a specified file or a remote destination.
Sending error messages to yourself by e-mail can be a good way of getting notified of specific errors.

Send an Error Message by E-Mail

In the example below we will send an e-mail with an error message and end the script, if a specific error occurs:

<?php
//error handler function
function customError($errno, $errstr)
  {
  echo "<b>Error:</b> [$errno] $errstr<br>";
  echo "Webmaster has been notified";
  error_log("Error: [$errno] $errstr",1,
  "someone@example.com","From: webmaster@example.com");
  }

//set error handler
set_error_handler("customError",E_USER_WARNING);

//trigger error
$test=2;
if ($test>1)
  {
  trigger_error("Value must be 1 or below",E_USER_WARNING);
  }
?>

The output of the code above should be something like this:

Error: [512] Value must be 1 or below
Webmaster has been notified

And the mail received from the code above looks like this:

Error: [512] Value must be 1 or below

This should not be used with all errors. Regular errors should be logged on the server using the default PHP logging system.

---------------------------

of Exceptions

When an exception is thrown, the code following it will not be executed, and PHP will try to find the matching "catch" block.
If an exception is not caught, a fatal error will be issued with an "Uncaught Exception" message.
Lets try to throw an exception without catching it:

<?php
//create function with an exception
function checkNum($number)
  {
  if($number>1)
    {
    throw new Exception("Value must be 1 or below");
    }
  return true;
  }

//trigger exception
checkNum(2);
?>

The code above will get an error like this:

Fatal error: Uncaught exception 'Exception'
with message 'Value must be 1 or below' in C:\webfolder\test.php:6
Stack trace: #0 C:\webfolder\test.php(12):
checkNum(28) #1 {main} thrown in C:\webfolder\test.php on line 6

Try, throw and catch

To avoid the error from the example above, we need to create the proper code to handle an exception.
Proper exception code should include:

Try - A function using an exception should be in a "try" block. If the exception does not trigger, the code will continue as normal. However if the exception triggers, an exception is "thrown"
Throw - This is how you trigger an exception. Each "throw" must have at least one "catch"
Catch - A "catch" block retrieves an exception and creates an object containing the exception information

Lets try to trigger an exception with valid code:

<?php
//create function with an exception
function checkNum($number)
  {
  if($number>1)
    {
    throw new Exception("Value must be 1 or below");
    }
  return true;
  }

//trigger exception in a "try" block
try
  {
  checkNum(2);
  //If the exception is thrown, this text will not be shown
  echo 'If you see this, the number is 1 or below';
  }

//catch exception
catch(Exception $e)
  {
  echo 'Message: ' .$e->getMessage();
  }
?>

The code above will get an error like this:

Message: Value must be 1 or below

Example explained:

The code above throws an exception and catches it:

The checkNum() function is created. It checks if a number is greater than 1. If it is, an exception is thrown
The checkNum() function is called in a "try" block
The exception within the checkNum() function is thrown
The "catch" block retrives the exception and creates an object ($e) containing the exception information
The error message from the exception is echoed by calling $e->getMessage() from the exception object

However, one way to get around the "every throw must have a catch" rule is to set a top level exception handler to handle errors that slip through.

Creating a Custom Exception Class

Creating a custom exception handler is quite simple. We simply create a special class with functions that can be called when an exception occurs in PHP. The class must be an extension of the exception class.
The custom exception class inherits the properties from PHP's exception class and you can add custom functions to it.
Lets create an exception class:

<?php
class customException extends Exception
  {
  public function errorMessage()
    {
    //error message
    $errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
    .': <b>'.$this->getMessage().'</b> is not a valid E-Mail address';
    return $errorMsg;
    }
  }

$email = "someone@example...com";

try
  {
  //check if
  if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
    {
    //throw exception if email is not valid
    throw new customException($email);
    }
  }

catch (customException $e)
  {
  //display custom message
  echo $e->errorMessage();
  }
?>

The new class is a copy of the old exception class with an addition of the errorMessage() function. Since it is a copy of the old class, and it inherits the properties and methods from the old class, we can use the exception class methods like getLine() and getFile() and getMessage().

Example explained:

The code above throws an exception and catches it with a custom exception class:

The customException() class is created as an extension of the old exception class. This way it inherits all methods and properties from the old exception class
The errorMessage() function is created. This function returns an error message if an e-mail address is invalid
The $email variable is set to a string that is not a valid e-mail address
The "try" block is executed and an exception is thrown since the e-mail address is invalid
The "catch" block catches the exception and displays the error message

Multiple Exceptions

It is possible for a script to use multiple exceptions to check for multiple conditions.
It is possible to use several if..else blocks, a switch, or nest multiple exceptions. These exceptions can use different exception classes and return different error messages:

<?php
class customException extends Exception
{
public function errorMessage()
{
//error message
$errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
.': <b>'.$this->getMessage().'</b> is not a valid E-Mail address';
return $errorMsg;
}
}

$email = "someone@example.com";

try
  {
  //check if
  if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
    {
    //throw exception if email is not valid
    throw new customException($email);
    }
  //check for "example" in mail address
  if(strpos($email, "example") !== FALSE)
    {
    throw new Exception("$email is an example e-mail");
    }
  }

catch (customException $e)
  {
  echo $e->errorMessage();
  }

catch(Exception $e)
  {
  echo $e->getMessage();
  }
?>

Example explained:

The code above tests two conditions and throws an exception if any of the conditions are not met:

The customException() class is created as an extension of the old exception class. This way it inherits all methods and properties from the old exception class
The errorMessage() function is created. This function returns an error message if an e-mail address is invalid
The $email variable is set to a string that is a valid e-mail address, but contains the string "example"
The "try" block is executed and an exception is not thrown on the first condition
The second condition triggers an exception since the e-mail contains the string "example"
The "catch" block catches the exception and displays the correct error message

If the exception thrown were of the class customException and there were no customException catch, only the base exception catch, the exception would be handled there.

Re-throwing Exceptions

Sometimes, when an exception is thrown, you may wish to handle it differently than the standard way. It is possible to throw an exception a second time within a "catch" block.
A script should hide system errors from users. System errors may be important for the coder, but is of no interest to the user. To make things easier for the user you can re-throw the exception with a user friendly message:

<?php
class customException extends Exception
  {
  public function errorMessage()
    {
    //error message
    $errorMsg = $this->getMessage().' is not a valid E-Mail address.';
    return $errorMsg;
    }
  }

$email = "someone@example.com";

try
  {
  try
    {
    //check for "example" in mail address
    if(strpos($email, "example") !== FALSE)
      {
      //throw exception if email is not valid
      throw new Exception($email);
      }
    }
  catch(Exception $e)
    {
    //re-throw exception
    throw new customException($email);
    }
  }

catch (customException $e)
  {
  //display custom message
  echo $e->errorMessage();
  }
?>

Example explained:

The code above tests if the email-address contains the string "example" in it, if it does, the exception is re-thrown:

The customException() class is created as an extension of the old exception class. This way it inherits all methods and properties from the old exception class
The errorMessage() function is created. This function returns an error message if an e-mail address is invalid
The $email variable is set to a string that is a valid e-mail address, but contains the string "example"
The "try" block contains another "try" block to make it possible to re-throw the exception
The exception is triggered since the e-mail contains the string "example"
The "catch" block catches the exception and re-throws a "customException"
The "customException" is caught and displays an error message

If the exception is not caught in its current "try" block, it will search for a catch block on "higher levels".

Set a Top Level Exception Handler

The set_exception_handler() function sets a user-defined function to handle all uncaught exceptions.

<?php
function myException($exception)
{
echo "<b>Exception:</b> " , $exception->getMessage();
}

set_exception_handler('myException');

throw new Exception('Uncaught Exception occurred');
?>

The output of the code above should be something like this:

Exception: Uncaught Exception occurred

In the code above there was no "catch" block. Instead, the top level exception handler triggered. This function should be used to catch uncaught exceptions.

Rules for exceptions

Code may be surrounded in a try block, to help catch potential exceptions
Each try block or "throw" must have at least one corresponding catch block
Multiple catch blocks can be used to catch different classes of exceptions
Exceptions can be thrown (or re-thrown) in a catch block within a try block

A simple rule: If you throw something, you have to catch it.
----------------

PHP filters are used to validate and filter data coming from insecure sources, like user input.

What is a PHP Filter?

A PHP filter is used to validate and filter data coming from insecure sources.
To test, validate and filter user input or custom data is an important part of any web application.
The PHP filter extension is designed to make data filtering easier and quicker.

Why use a Filter?

Almost all web applications depend on external input. Usually this comes from a user or another application (like a web service). By using filters you can be sure your application gets the correct input type.
You should always filter all external data!
Input filtering is one of the most important application security issues.
What is external data?

Input data from a form
Cookies
Web services data
Server variables
Database query results

Functions and Filters

To filter a variable, use one of the following filter functions:

filter_var() - Filters a single variable with a specified filter
filter_var_array() - Filter several variables with the same or different filters
filter_input - Get one input variable and filter it
filter_input_array - Get several input variables and filter them with the same or different filters

In the example below, we validate an integer using the filter_var() function:

<?php
$int = 123;

if(!filter_var($int, FILTER_VALIDATE_INT))
  {
  echo("Integer is not valid");
  }
else
  {
  echo("Integer is valid");
  }
?>

The code above uses the "FILTER_VALIDATE_INT" filter to filter the variable. Since the integer is valid, the output of the code above will be: "Integer is valid".
If we try with a variable that is not an integer (like "123abc"), the output will be: "Integer is not valid".
For a complete list of functions and filters, visit our PHP Filter Reference.

Validating and Sanitizing

There are two kinds of filters:
Validating filters:

Are used to validate user input
Strict format rules (like URL or E-Mail validating)
Returns the expected type on success or FALSE on failure

Sanitizing filters:

Are used to allow or disallow specified characters in a string
No data format rules
Always return the string

Options and Flags

Options and flags are used to add additional filtering options to the specified filters.
Different filters have different options and flags.
In the example below, we validate an integer using the filter_var() and the "min_range" and "max_range" options:

<?php
$var=300;

$int_options = array(
"options"=>array
  (
  "min_range"=>0,
  "max_range"=>256
  )
);

if(!filter_var($var, FILTER_VALIDATE_INT, $int_options))
  {
  echo("Integer is not valid");
  }
else
  {
  echo("Integer is valid");
  }
?>

Like the code above, options must be put in an associative array with the name "options". If a flag is used it does not need to be in an array.
Since the integer is "300" it is not in the specified range, and the output of the code above will be: "Integer is not valid".
For a complete list of functions and filters, visit our PHP Filter Reference. Check each filter to see what options and flags are available.

Validate Input

Let's try validating input from a form.
The first thing we need to do is to confirm that the input data we are looking for exists.
Then we filter the input data using the filter_input() function.
In the example below, the input variable "email" is sent to the PHP page:

<?php
if(!filter_has_var(INPUT_GET, "email"))
  {
  echo("Input type does not exist");
  }
else
  {
  if (!filter_input(INPUT_GET, "email", FILTER_VALIDATE_EMAIL))
    {
    echo "E-Mail is not valid";
    }
  else
    {
    echo "E-Mail is valid";
    }
  }
?>

Example Explained

The example above has an input (email) sent to it using the "GET" method:

Check if an "email" input variable of the "GET" type exist
If the input variable exists, check if it is a valid e-mail address

Sanitize Input

Let's try cleaning up an URL sent from a form.
First we confirm that the input data we are looking for exists.
Then we sanitize the input data using the filter_input() function.
In the example below, the input variable "url" is sent to the PHP page:

<?php
if(!filter_has_var(INPUT_POST, "url"))
  {
  echo("Input type does not exist");
  }
else
  {
  $url = filter_input(INPUT_POST,
  "url", FILTER_SANITIZE_URL);
  }
?>

Example Explained

The example above has an input (url) sent to it using the "POST" method:

Check if the "url" input of the "POST" type exists
If the input variable exists, sanitize (take away invalid characters) and store it in the $url variable

If the input variable is a string like this "http://www.W3ååSchøøools.com/", the $url variable after the sanitizing will look like this:

http://www.W3Schools.com/

Filter Multiple Inputs

A form almost always consist of more than one input field. To avoid calling the filter_var or filter_input functions over and over, we can use the filter_var_array or the filter_input_array functions.
In this example we use the filter_input_array() function to filter three GET variables. The received GET variables is a name, an age and an e-mail address:

<?php
$filters = array
  (
  "name" => array
    (
    "filter"=>FILTER_SANITIZE_STRING
    ),
  "age" => array
    (
    "filter"=>FILTER_VALIDATE_INT,
    "options"=>array
      (
      "min_range"=>1,
      "max_range"=>120
      )
    ),
  "email"=> FILTER_VALIDATE_EMAIL
  );

$result = filter_input_array(INPUT_GET, $filters);

if (!$result["age"])
  {
  echo("Age must be a number between 1 and 120.<br>");
  }
elseif(!$result["email"])
  {
  echo("E-Mail is not valid.<br>");
  }
else
  {
  echo("User input is valid");
  }
?>

Example Explained

The example above has three inputs (name, age and email) sent to it using the "GET" method:

Set an array containing the name of input variables and the filters used on the specified input variables
Call the filter_input_array() function with the GET input variables and the array we just set
Check the "age" and "email" variables in the $result variable for invalid inputs. (If any of the input variables are invalid, that input variable will be FALSE after the filter_input_array() function)

The second parameter of the filter_input_array() function can be an array or a single filter ID.
If the parameter is a single filter ID all values in the input array are filtered by the specified filter.
If the parameter is an array it must follow these rules:

Must be an associative array containing an input variable as an array key (like the "age" input variable)
The array value must be a filter ID or an array specifying the filter, flags and options

Using Filter Callback

It is possible to call a user defined function and use it as a filter using the FILTER_CALLBACK filter. This way, we have full control of the data filtering.
You can create your own user defined function or use an existing PHP function
The function you wish to use to filter is specified the same way as an option is specified. In an associative array with the name "options"
In the example below, we use a user created function to convert all "_" to whitespaces:

<?php
function convertSpace($string)
{
return str_replace("_", " ", $string);
}

$string = "Peter_is_a_great_guy!";

echo filter_var($string, FILTER_CALLBACK,
array("options"=>"convertSpace"));
?>

The result from the code above should look like this:

Peter is a great guy!

Example Explained

The example above converts all "_" to whitespaces:

Create a function to replace "_" to whitespaces
Call the filter_var() function with the FILTER_CALLBACK filter and an array containing our function

PHP Basic

<!DOCTYPE html>
<html>
<body>

<h1>My first PHP page</h1>

<?php
echo "Hello World!";
?>

</body>
</html>
----------------------------
<!DOCTYPE html>
<html>
<body>

<?php
// This is a single line comment

# This is also a single line comment

/*
This is a multiple lines comment block
that spans over more than
one line
*/
?>

</body>
</html>
---------------------------------------

PHP Case Sensitivity

In PHP, all user-defined functions, classes, and keywords (e.g. if, else, while, echo, etc.) are case-insensitive.
In the example below, all three echo statements below are legal (and equal):

Example

<!DOCTYPE html>
<html>
<body>

<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>

</body>
</html>

-------------------------------------

However; in PHP, all variables are case-sensitive.
In the example below, only the first statement will display the value of the $color variable (this is because $color, $COLOR, and $coLOR are treated as three different variables):

Example

<!DOCTYPE html>
<html>
<body>

<?php
$color="red";
echo "My car is " . $color . "<br>";
echo "My house is " . $COLOR . "<br>";
echo "My boat is " . $coLOR . "<br>";
?>

</body>
</html>

-------------------------

Variables are "containers" for storing information:

Example

<?php
$x=5;
$y=6;
$z=$x+$y;
echo $z;
?>

-------------

Creating (Declaring) PHP Variables

PHP has no command for declaring a variable.
A variable is created the moment you first assign a value to it:

Example

<?php
$txt="Hello world!";
$x=5;
$y=10.5;
?>

-----------------------------------

Local and Global Scope

A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function.
A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function.
The following example tests variables with local and global scope:

Example

<?php
$x=5; // global scope

function myTest()
{
$y=10; // local scope
echo "<p>Test variables inside the function:<p>";
echo "Variable x is: $x";
echo "<br>";
echo "Variable y is: $y";
}

myTest();

echo "<p>Test variables outside the function:<p>";
echo "Variable x is: $x";
echo "<br>";
echo "Variable y is: $y";
?>

---------------------------------------

PHP The global Keyword

The global keyword is used to access a global variable from within a function.
To do this, use the global keyword before the variables (inside the function):

Example

<?php
$x=5;
$y=10;

function myTest()
{
global $x,$y;
$y=$x+$y;
}

myTest();
echo $y; // outputs 15
?>

PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.
The example above can be rewritten like this:

Example

<?php
$x=5;
$y=10;

function myTest()
{
$GLOBALS['y']=$GLOBALS['x']+$GLOBALS['y'];
}

myTest();
echo $y; // outputs 15
?>

PHP The static Keyword

Normally, when a function is completed/executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job.
To do this, use the static keyword when you first declare the variable:

Example

<?php

function myTest()
{
static $x=0;
echo $x;
$x++;
}

myTest();
myTest();
myTest();

?>

Then, each time the function is called, that variable will still have the information it contained from the last time the function was called.
Note: The variable is still local to the function.

----------------------------

In PHP there is two basic ways to get output: echo and print.

In this tutorial we use echo (and print) in almost every example. So, this chapter contains a little more info about those two output statements.

PHP echo and print Statements

There are some difference between echo and print:

echo - can output one or more strings
print - can only output one string, and returns always 1

Tip: echo is marginally faster compare to print as echo does not return any value.

The PHP echo Statement

echo is a language construct, and can be used with or without parantheses: echo or echo().
Display Strings
The following example shows how to display different strings with the echo command (also notice that the strings can contain HTML markup):

Example

<?php
echo "<h2>PHP is fun!</h2>";
echo "Hello world!<br>";
echo "I'm about to learn PHP!<br>";
echo "This", " string", " was", " made", " with multiple parameters.";
?>

Display Variables
The following example shows how to display strings and variables with the echo command:

Example

<?php
$txt1="Learn PHP";
$txt2="W3Schools.com";
$cars=array("Volvo","BMW","Toyota");

echo $txt1;
echo "<br>";
echo "Study PHP at $txt2";
echo "My car is a {$cars[0]}";
?>

The PHP print Statement

print is also a language construct, and can be used with or without parantheses: print or print().
Display Strings
The following example shows how to display different strings with the print command (also notice that the strings can contain HTML markup):

Example

<?php
print "<h2>PHP is fun!</h2>";
print "Hello world!<br>";
print "I'm about to learn PHP!";
?>

Display Variables
The following example shows how to display strings and variables with the print command:

Example

<?php
$txt1="Learn PHP";
$txt2="W3Schools.com";
$cars=array("Volvo","BMW","Toyota");

print $txt1;
print "<br>";
print "Study PHP at $txt2";
print "My car is a {$cars[0]}";
?>

----------------

PHP Strings

A string is a sequence of characters, like "Hello world!".
A string can be any text inside quotes. You can use single or double quotes:

Example

<?php
$x = "Hello world!";
echo $x;
echo "<br>";
$x = 'Hello world!';
echo $x;
?>

PHP Integers

An integer is a number without decimals.
Rules for integers:

An integer must have at least one digit (0-9)
An integer cannot contain comma or blanks
An integer must not have a decimal point
An integer can be either positive or negative
Integers can be specified in three formats: decimal (10-based), hexadecimal (16-based - prefixed with 0x) or octal (8-based - prefixed with 0)

In the following example we will test different numbers. The PHP var_dump() function returns the data type and value of variables:

Example

<?php
$x = 5985;
var_dump($x);
echo "<br>";
$x = -345; // negative number
var_dump($x);
echo "<br>";
$x = 0x8C; // hexadecimal number
var_dump($x);
echo "<br>";
$x = 047; // octal number
var_dump($x);
?>

PHP Floating Point Numbers

A floating point number is a number with a decimal point or a number in exponential form.
In the following example we will test different numbers. The PHP var_dump() function returns the data type and value of variables:

Example

<?php
$x = 10.365;
var_dump($x);
echo "<br>";
$x = 2.4e3;
var_dump($x);
echo "<br>";
$x = 8E-5;
var_dump($x);
?>

PHP Booleans

Booleans can be either TRUE or FALSE.

var x=true;
var y=false;

Booleans are often used in conditional testing. You will learn more about conditional testing in a later chapter of this tutorial.

PHP Arrays

An array stores multiple values in one single variable.
In the following example we create an array, and then use the PHP var_dump() function to return the data type and value of the array:

Example

<?php
$cars=array("Volvo","BMW","Toyota");
var_dump($cars);
?>

PHP Objects

An object is a data type which stores data and information on how to process that data.
In PHP, an object must be explicitly declared.
First we must declare a class of object. For this, we use the class keyword. A class is a structure that can contain properties and methods.
We then define the data type in the object class, and then we use the data type in instances of that class:

Example

<?php
class Car
{
var $color;
function Car($color="green")
{
$this->color = $color;
}
function what_color()
{
return $this->color;
}
}
?>

PHP NULL Value

The special NULL value represents that a variable has no value. NULL is the only possible value of data type NULL.
The NULL value identifies whether a variable is empty or not. Also useful to differentiate between the empty string and null values of databases.
Variables can be emptied by setting the value to NULL:

Example

<?php
$x="Hello world!";
$x=null;
var_dump($x);
?>

A string is a sequence of characters, like "Hello world!".

PHP String Functions

In this chapter we will look at some commonly used functions to manipulate strings.

The PHP strlen() function

The strlen() function returns the length of a string, in characters.
The example below returns the length of the string "Hello world!":

Example

<?php
echo strlen("Hello world!");
?>

The output of the code above will be: 12

The PHP strpos() function

The strpos() function is used to search for a specified character or text within a string.
If a match is found, it will return the character position of the first match. If no match is found, it will return FALSE.
The example below searches for the text "world" in the string "Hello world!":

Example

<?php
echo strpos("Hello world!","world");
?>

The output of the code above will be: 6.
-------------------------------

Constants are like variables except that once they are defined they cannot be changed or undefined.

PHP Constants

A constant is an identifier (name) for a simple value. The value cannot be changed during the script.
A valid constant name starts with a letter or underscore (no $ sign before the constant name).
Note: Unlike valriables, constants are automatically global across the entire script.

Set a PHP Constant

To set a constant, use the define() function - it takes three parameters: The first parameter defines the name of the constant, the second parameter defines the value of the constant, and the optional third parameter specifies whether the constant name should be case-insensitive. By default, the constant name is not case-insensitive.
The example below creates a case-sensitive constant, with the value of "Welcome to W3Schools.com!":

Example

<?php
define("GREETING", "Welcome to W3Schools.com!");
echo GREETING;
?>

The example below creates a case-insensitive constant, with the value of "Welcome to W3Schools.com!":

Example

<?php
define("GREETING", "Welcome to W3Schools.com!", true);
echo greeting;
?>

----------------------------

This chapter shows the different operators that can be used in PHP scripts.

PHP Arithmetic Operators

Operator	Name	Example	Result
+	Addition	$x + $y	Sum of $x and $y
-	Subtraction	$x - $y	Difference of $x and $y
*	Multiplication	$x * $y	Product of $x and $y
/	Division	$x / $y	Quotient of $x and $y
%	Modulus	$x % $y	Remainder of $x divided by $y

The example below shows the different results of using the different arithmetic operators:

Example

<?php
$x=10;
$y=6;
echo ($x + $y); // outputs 16
echo ($x - $y); // outputs 4
echo ($x * $y); // outputs 60
echo ($x / $y); // outputs 1.6666666666667
echo ($x % $y); // outputs 4
?>

-----------------------

PHP Assignment Operators

The PHP assignment operators is used to write a value to a variable.
The basic assignment operator in PHP is "=". It means that the left operand gets set to the value of the assignment expression on the right.

Assignment	Same as...	Description
x = y	x = y	The left operand gets set to the value of the expression on the right
x += y	x = x + y	Addition
x -= y	x = x - y	Subtraction
x *= y	x = x * y	Multiplication
x /= y	x = x / y	Division
x %= y	x = x % y	Modulus

The example below shows the different results of using the different assignment operators:

Example

<?php
$x=10;
echo $x; // outputs 10

$y=20;
$y += 100;
echo $y; // outputs 120

$z=50;
$z -= 25;
echo $z; // outputs 25

$i=5;
$i *= 6;
echo $i; // outputs 30

$j=10;
$j /= 5;
echo $j; // outputs 2

$k=15;
$k %= 4;
echo $k; // outputs 3
?>

PHP String Operators

Operator	Name	Example	Result
.	Concatenation	$txt1 = "Hello" $txt2 = $txt1 . " world!"	Now $txt2 contains "Hello world!"
.=	Concatenation assignment	$txt1 = "Hello" $txt1 .= " world!"	Now $txt1 contains "Hello world!"

The example below shows the results of using the string operators:

Example

<?php
$a = "Hello";
$b = $a . " world!";
echo $b; // outputs Hello world!

$x="Hello";
$x .= " world!";
echo $x; // outputs Hello world!
?>

PHP Increment / Decrement Operators

Operator	Name	Description
++$x	Pre-increment	Increments $x by one, then returns $x
$x++	Post-increment	Returns $x, then increments $x by one
--$x	Pre-decrement	Decrements $x by one, then returns $x
$x--	Post-decrement	Returns $x, then decrements $x by one

The example below shows the different results of using the different increment/decrement operators:

Example

<?php
$x=10;
echo ++$x; // outputs 11

$y=10;
echo $y++; // outputs 10

$z=5;
echo --$z; // outputs 4

$i=5;
echo $i--; // outputs 5
?>

PHP Comparison Operators

The PHP comparison operators are used to compare two values (number or string):

Operator	Name	Example	Result
==	Equal	$x == $y	True if $x is equal to $y
===	Identical	$x === $y	True if $x is equal to $y, and they are of the same type
!=	Not equal	$x != $y	True if $x is not equal to $y
<>	Not equal	$x <> $y	True if $x is not equal to $y
!==	Not identical	$x !== $y	True if $x is not equal to $y, or they are not of the same type
>	Greater than	$x > $y	True if $x is greater than $y
<	Less than	$x < $y	True if $x is less than $y
>=	Greater than or equal to	$x >= $y	True if $x is greater than or equal to $y
<=	Less than or equal to	$x <= $y	True if $x is less than or equal to $y

The example below shows the different results of using some of the comparison operators:

Example

<?php
$x=100;
$y="100";

var_dump($x == $y);
echo "<br>";
var_dump($x === $y);
echo "<br>";
var_dump($x != $y);
echo "<br>";
var_dump($x !== $y);
echo "<br>";

$a=50;
$b=90;

var_dump($a > $b);
echo "<br>";
var_dump($a < $b);
?>

PHP Logical Operators

Operator	Name	Example	Result
and	And	$x and $y	True if both $x and $y are true
or	Or	$x or $y	True if either $x or $y is true
xor	Xor	$x xor $y	True if either $x or $y is true, but not both
&&	And	$x && $y	True if both $x and $y are true
\|\|	Or	$x \|\| $y	True if either $x or $y is true
!	Not	!$x	True if $x is not true

PHP Array Operators

The PHP array operators are used to compare arrays:

Operator	Name	Example	Result
+	Union	$x + $y	Union of $x and $y (but duplicate keys are not overwritten)
==	Equality	$x == $y	True if $x and $y have the same key/value pairs
===	Identity	$x === $y	True if $x and $y have the same key/value pairs in the same order and of the same types
!=	Inequality	$x != $y	True if $x is not equal to $y
<>	Inequality	$x <> $y	True if $x is not equal to $y
!==	Non-identity	$x !== $y	True if $x is not identical to $y

The example below shows the different results of using the different array operators:

Example

<?php
$x = array("a" => "red", "b" => "green");
$y = array("c" => "blue", "d" => "yellow");
$z = $x + $y; // union of $x and $y
var_dump($z);
var_dump($x == $y);
var_dump($x === $y);
var_dump($x != $y);
var_dump($x <> $y);
var_dump($x !== $y);
?>

Conditional statements are used to perform different actions based on different conditions.

PHP Conditional Statements

Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.
In PHP we have the following conditional statements:

if statement - executes some code only if a specified condition is true
if...else statement - executes some code if a condition is true and another code if the condition is false
if...elseif....else statement - selects one of several blocks of code to be executed
switch statement - selects one of many blocks of code to be executed

PHP - The if Statement

The if statement is used to execute some code only if a specified condition is true.

Syntax

if (condition)
{
code to be executed if condition is true;
}

The example below will output "Have a good day!" if the current time (HOUR) is less than 20:

Example

<?php
$t=date("H");
if ($t<"20")
{
echo "Have a good day!";
}
?>

PHP - The if...else Statement

Use the if....else statement to execute some code if a condition is true and another code if the condition is false.

Syntax

if (condition)
{
code to be executed if condition is true;
}
else
{
code to be executed if condition is false;
}

The example below will output "Have a good day!" if the current time is less than 20, and "Have a good night!" otherwise:

Example

<?php
$t=date("H");
if ($t<"20")
{
echo "Have a good day!";
}
else
{
echo "Have a good night!";
}
?>

PHP - The if...elseif....else Statement

Use the if....elseif...else statement to select one of several blocks of code to be executed.

Syntax

if (condition)
{
  code to be executed if condition is true;
}
elseif (condition)
{
  code to be executed if condition is true;
}
else
{
  code to be executed if condition is false; }

The example below will output "Have a good morning!" if the current time is less than 10, and "Have a good day!" if the current time is less than 20. Otherwise it will output "Have a good night!":

Example

<?php
$t=date("H");
if ($t<"10")
{
echo "Have a good morning!";
}
elseif ($t<"20")
{
echo "Have a good day!";
}
else
{
echo "Have a good night!";
}
?>

he switch statement is used to perform different actions based on different conditions.

The PHP switch Statement

Use the switch statement to select one of many blocks of code to be executed.

Syntax

switch (n)
{
case label1:
  code to be executed if n=label1;
  break;
case label2:
  code to be executed if n=label2;
  break;
case label3:
  code to be executed if n=label3;
  break;
...
default:
  code to be executed if n is different from all labels;
}

This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically. The default statement is used if no match is found.

Example

<?php
$favcolor="red";
switch ($favcolor)
{
case "red":
echo "Your favorite color is red!";
break;
case "blue":
echo "Your favorite color is blue!";
break;
case "green":
echo "Your favorite color is green!";
break;
default:
echo "Your favorite color is neither red, blue, or green!";
}
?>

PHP while loops execute a block of code while the specified condition is true.

PHP Loops

Often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal code-lines in a script, we can use loops to perform a task like this.
In PHP, we have the following looping statements:

while - loops through a block of code as long as the specified condition is true
do...while - loops through a block of code once, and then repeats the loop as long as the specified condition is true
for - loops through a block of code a specified number of times
foreach - loops through a block of code for each element in an array

The PHP while Loop

The while loop executes a block of code as long as the specified condition is true.

Syntax

while (condition is true)
{
code to be executed;
}

The example below first sets a variable $x to 1 ($x=1;). Then, the while loop will continue to run as long as $x is less than, or equal to 5. $x will increase by 1 each time the loop runs ($x++;):

Example

<?php
$x=1;
while($x<=5)
{
echo "The number is: $x <br>";
$x++;
}
?>

The PHP do...while Loop

The do...while loop will always execute the block of code once, it will then check the condition, and repeat the loop while the specified condition is true.

Syntax

do
{
code to be executed;
}
while (condition is true);

The example below first sets a variable $x to 1 ($x=1;). Then, the do while loop will write some output, and then increment the variable $x with 1. Then the condition is checked (is $x less than, or equal to 5?), and the loop will continue to run as long as $x is less than, or equal to 5:

Example

<?php
$x=1;
do
{
echo "The number is: $x <br>";
$x++;
}
while ($x<=5)
?>

Notice that in a do while loop the condition is tested AFTER executing the statements within the loop. This means that the do while loop would execute its statements at least once, even if the condition fails the first time.
The example below sets the $x variable to 6, then it runs the loop, and then the condition is checked:

Example

<?php
$x=6;
do
{
echo "The number is: $x <br>";
$x++;
}
while ($x<=5)
?>

PHP for loops execute a block of code a specified number of times.

The PHP for Loop

The for loop is used when you know in advance how many times the script should run.

Syntax

for (init counter; test counter; increment counter)
{
code to be executed;
}

Parameters:

init counter: Initialize the loop counter value
test counter: Evaluated for each loop iteration. If it evaluates to TRUE, the loop continues. If it evaluates to FALSE, the loop ends.
increment counter: Increases the loop counter value

The example below displays the numbers from 0 to 10:

Example

<?php
for ($x=0; $x<=10; $x++)
{
echo "The number is: $x <br>";
}
?>

The PHP foreach Loop

The foreach loop works only on arrays, and is used to loop through each key/value pair in an array.

Syntax

foreach ($array as $value)
{
code to be executed;
}

For every loop iteration, the value of the current array element is assigned to $value and the array pointer is moved by one, until it reaches the last array element.
The following example demonstrates a loop that will output the values of the given array ($colors):

Example

<?php
$colors = array("red","green","blue","yellow");
foreach ($colors as $value)
{
echo "$value <br>";
}
?>

The real power of PHP comes from its functions; it has more than 1000 built-in functions.

PHP User Defined Functions

Besides the built-in PHP functions, we can create our own functions.
A function is a block of statements that can be used repeatadly in a program.
A function will not execute immediately when a page loads.
A function will be executed by a call to the function.

Create a User Defined Function in PHP

A user defined function declaration starts with the word "function":

Syntax

function functionName()
{
code to be executed;
}

Note: A function name can start with a letter or underscore (not a number).
Tip: Give the function a name that reflects what the function does!

	Remember that function names are case-insensitive.

In the example below, we create a function named "writeMsg()". The opening curly brace ( { ) indicates the beginning of the function code and the closing curly brace ( } ) indicates the end of the function. The function outputs "Hello world!". To call the function, just write its name:

Example

<?php
function writeMsg()
{
echo "Hello world!";
}

writeMsg(); // call the function
?>

PHP Function Arguments

Information can be passed to functions through arguments. An argument is just like a variable.
Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just seperate them with a comma.
The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:

Example

<?php
function familyName($fname)
{
echo "$fname Refsnes.<br>";
}

familyName("Jani");
familyName("Hege");
familyName("Stale");
familyName("Kai Jim");
familyName("Borge");
?>

The following example has a function with two arguments ($fname and $year):

Example

<?php
function familyName($fname,$year)
{
echo "$fname Refsnes. Born in $year <br>";
}

familyName("Hege","1975");
familyName("Ståle","1978");
familyName("Kai Jim","1983");
?>

PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

Example

<?php
function setHeight($minheight=50)
{
echo "The height is : $minheight <br>";
}

setHeight(350);
setHeight(); // will use the default value of 50
setHeight(135);
setHeight(80);
?>

PHP Functions - Returning values

To let a function return a value, use the return statement:

Example

<?php
function sum($x,$y)
{
$z=$x+$y;
return $z;
}

echo "5 + 10 = " . sum(5,15) . "<br>";
echo "7 + 13 = " . sum(7,13) . "<br>";
echo "2 + 4 = " . sum(2,4);
?>

An array stores multiple values in one single variable:

Example

<?php
$cars=array("Volvo","BMW","Toyota");
echo "I like " . $cars[0] . ", " . $cars[1] . " and " . $cars[2] . ".";
?>

Run example »

What is an Array?

An array is a special variable, which can hold more than one value at a time.
If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

$cars1="Volvo";
$cars2="BMW";
$cars3="Toyota";

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?
The solution is to create an array!
An array can hold many values under a single name, and you can access the values by referring to an index number.

Create an Array in PHP

In PHP, the array() function is used to create an array:

array();

In PHP, there are three types of arrays:

Indexed arrays - Arrays with numeric index
Associative arrays - Arrays with named keys
Multidimensional arrays - Arrays containing one or more arrays

PHP Indexed Arrays

There are two ways to create indexed arrays:
The index can be assigned automatically (index always starts at 0):

$cars=array("Volvo","BMW","Toyota");

or the index can be assigned manually:

$cars[0]="Volvo";
$cars[1]="BMW";
$cars[2]="Toyota";

The following example creates an indexed array named $cars, assigns three elements to it, and then prints a text containing the array values:

Example

<?php
$cars=array("Volvo","BMW","Toyota");
echo "I like " . $cars[0] . ", " . $cars[1] . " and " . $cars[2] . ".";
?>

Get The Length of an Array - The count() Function

The count() function is used to return the length (the number of elements) of an array:

Example

<?php
$cars=array("Volvo","BMW","Toyota");
echo count($cars);
?>

Loop Through an Indexed Array

To loop through and print all the values of an indexed array, you could use a for loop, like this:

Example

<?php
$cars=array("Volvo","BMW","Toyota");
$arrlength=count($cars);

for($x=0;$x<$arrlength;$x++)
{
echo $cars[$x];
echo "<br>";
}
?>

PHP Associative Arrays

Associative arrays are arrays that use named keys that you assign to them.
There are two ways to create an associative array:

$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");

or:

$age['Peter']="35";
$age['Ben']="37";
$age['Joe']="43";

The named keys can then be used in a script:

Example

<?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");
echo "Peter is " . $age['Peter'] . " years old.";
?>

Loop Through an Associative Array

To loop through and print all the values of an associative array, you could use a foreach loop, like this:

Example

<?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");

foreach($age as $x=>$x_value)
{
echo "Key=" . $x . ", Value=" . $x_value;
echo "<br>";
}
?>

The elements in an array can be sorted in alphabetical or numerical order, descending or ascending.

PHP - Sort Functions For Arrays

In this chapter, we will go through the following PHP array sort functions:

sort() - sort arrays in ascending order
rsort() - sort arrays in descending order
asort() - sort associative arrays in ascending order, according to the value
ksort() - sort associative arrays in ascending order, according to the key
arsort() - sort associative arrays in descending order, according to the value
krsort() - sort associative arrays in descending order, according to the key

Sort Array in Ascending Order - sort()

The following example sorts the elements of the $cars array in ascending alphabetical order:

Example

<?php
$cars=array("Volvo","BMW","Toyota");
sort($cars);
?>

The following example sorts the elements of the $numbers array in ascending numerical order:

Example

<?php
$numbers=array(4,6,2,22,11);
sort($numbers);
?>

Sort Array in Descending Order - rsort()

The following example sorts the elements of the $cars array in descending alphabetical order:

Example

<?php
$cars=array("Volvo","BMW","Toyota");
rsort($cars);
?>

The following example sorts the elements of the $numbers array in descending numerical order:

Example

<?php
$numbers=array(4,6,2,22,11);
rsort($numbers);
?>

Sort Array in Ascending Order, According to Value - asort()

The following example sorts an associative array in ascending order, according to the value:

Example

<?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");
asort($age);
?>

Sort Array in Ascending Order, According to Key - ksort()

The following example sorts an associative array in ascending order, according to the key:

Example

<?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");
ksort($age);
?>

Sort Array in Descending Order, According to Value - arsort()

The following example sorts an associative array in descending order, according to the value:

Example

<?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");
arsort($age);
?>

Sort Array in Descending Order, According to Key - krsort()

The following example sorts an associative array in descending order, according to the key:

Example

<?php
$age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43");
krsort($age);
?>

Superglobals were introduced in PHP 4.1.0, and are built-in variables that are always available in all scopes.

PHP Global Variables - Superglobals

Several predefined variables in PHP are "superglobals", which means that they are always accessible, regardless of scope - and you can access them from any function, class or file without having to do anything special.
The PHP superglobal variables are:

$GLOBALS
$_SERVER
$_REQUEST
$_POST
$_GET
$_FILES
$_ENV
$_COOKIE
$_SESSION

This chapter will explain some of the superglobals, and the rest will be explained in later chapters.

PHP $GLOBAL

$GLOBAL is a PHP super global variable which is used to access global variables from anywhere in the PHP script (also from within functions or methods).
PHP stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable.
The example below shows how to use the super global variable $GLOBAL:

Example

<?php
$x = 75;
$y = 25;

function addition()
{
$GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y'];
}

addition();
echo $z;
?>

In the example above, since z is a variable present within the $GLOBALS array, it is also accessible form outside the function!

PHP $_SERVER

$_SERVER is a PHP super global variable which holds information about headers, paths, and script locations.
The example below shows how to use some of the elements in $_SERVER:

Example

<?php
echo $_SERVER['PHP_SELF'];
echo "<br>";
echo $_SERVER['SERVER_NAME'];
echo "<br>";
echo $_SERVER['HTTP_HOST'];
echo "<br>";
echo $_SERVER['HTTP_REFERER'];
echo "<br>";
echo $_SERVER['HTTP_USER_AGENT'];
echo "<br>";
echo $_SERVER['SCRIPT_NAME'];
?>

The following table lists the most important elements that can go inside $_SERVER:

Element/Code	Description
$_SERVER['PHP_SELF']	Returns the filename of the currently executing script
$_SERVER['GATEWAY_INTERFACE']	Returns the version of the Common Gateway Interface (CGI) the server is using
$_SERVER['SERVER_ADDR']	Returns the IP address of the host server
$_SERVER['SERVER_NAME']	Returns the name of the host server (such as www.w3schools.com)
$_SERVER['SERVER_SOFTWARE']	Returns the server identification string (such as Apache/2.2.24)
$_SERVER['SERVER_PROTOCOL']	Returns the name and revision of the information protocol (such as HTTP/1.1)
$_SERVER['REQUEST_METHOD']	Returns the request method used to access the page (such as POST)
$_SERVER['REQUEST_TIME']	Returns the timestamp of the start of the request (such as 1377687496)
$_SERVER['QUERY_STRING']	Returns the query string if the page is accessed via a query string
$_SERVER['HTTP_ACCEPT']	Returns the Accept header from the current request
$_SERVER['HTTP_ACCEPT_CHARSET']	Returns the Accept_Charset header from the current request (such as utf-8,ISO-8859-1)
$_SERVER['HTTP_HOST']	Returns the Host header from the current request
$_SERVER['HTTP_REFERER']	Returns the complete URL of the current page (not reliable because not all user-agents support it)
$_SERVER['HTTPS']	Is the script queried through a secure HTTP protocol
$_SERVER['REMOTE_ADDR']	Returns the IP address from where the user is viewing the current page
$_SERVER['REMOTE_HOST']	Returns the Host name from where the user is viewing the current page
$_SERVER['REMOTE_PORT']	Returns the port being used on the user's machine to communicate with the web server
$_SERVER['SCRIPT_FILENAME']	Returns the absolute pathname of the currently executing script
$_SERVER['SERVER_ADMIN']	Returns the value given to the SERVER_ADMIN directive in the web server configuration file (if your script runs on a virtual host, it will be the value defined for that virtual host) (such as someone@w3scholls.com)
$_SERVER['SERVER_PORT']	Returns the port on the server machine being used by the web server for communication (such as 80)
$_SERVER['SERVER_SIGNATURE']	Returns the server version and virtual host name which are added to server-generated pages
$_SERVER['PATH_TRANSLATED']	Returns the file system based path to the current script
$_SERVER['SCRIPT_NAME']	Returns the path of the current script
$_SERVER['SCRIPT_URI']	Returns the URI of the current page

PHP $_REQUEST

PHP $_REQUEST is used to collect data after submitting an HTML form.
The example below shows a form with an input field and a submit button. When a user submits the data by clicking on "Submit", the form data is sent to the file specified in the action attribute of the <form> tag. In this example, we point to this file itself for processing form data. If you wish to use another PHP file to process form data, replace that with the filename of your choice. Then, we can use the super global variable $_REQUEST to collect the value of the input field:

Example

PHP $_POST

PHP $_POST is widely used to collect form data after submitting an HTML form with method="post". $_POST is also widely used to pass variables.
The example below shows a form with an input field and a submit button. When a user submits the data by clicking on "Submit", the form data is sent to the file specified in the action attribute of the <form> tag. In this example, we point to this file itself for processing form data. If you wish to use another PHP file to process form data, replace that with the filename of your choice. Then, we can use the super global variable $_POST to collect the value of the input field:

Example

PHP $_GET

PHP $_GET can also be used to collect form data after submitting an HTML form with method="get".
$_GET can also collect data sent in the URL.
Assume we have an HTML page that contains a hyperlink with parameters:

When a user clicks on the link "Test $GET", the parameters "subject" and "web" is sent to "test_get.php", and you can then acces their values in "test_get.php" with $_GET.
The example below shows the code in "test_get.php":

Example

The PHP superglobals $_GET and $_POST are used to collect form-data.

PHP Form Handling

This chapter shows how to collect form-data from users using POST and GET method from various form controls.

Example

The example below contains an HTML form with two input fields and a submit button:

When a user fills out the form above and clicks on the submit button, the form data is sent to a PHP file, called "welcome.php":
"welcome.php" looks like this:

<html>
<body>

Welcome <?php echo $_POST["fname"]; ?>!<br>
You are <?php echo $_POST["age"]; ?> years old.

</body>
</html>

Output could be something like this:

Welcome John!
You are 28 years old.

The PHP $_GET and $_POST variables will be explained in the next chapters.

Form Validation

User input should be validated on the browser whenever possible (by client scripts). Browser validation is faster and reduces the server load.
You should consider server validation if the user input will be inserted into a database. A good way to validate a form on the server is to post the form to itself, instead of jumping to a different page. The user will then get the error messages on the same page as the form. This makes it easier to discover the error.

In PHP, the predefined $_GET variable is used to collect values in a form with method="get".

The $_GET Variable

The predefined $_GET variable is used to collect values in a form with method="get"
Information sent from a form with the GET method is visible to everyone (it will be displayed in the browser's address bar) and has limits on the amount of information to send.

Example

When the user clicks the "Submit" button, the URL sent to the server could look something like this:

http://www.w3schools.com/welcome.php?fname=Peter&age=37

The "welcome.php" file can now use the $_GET variable to collect form data (the names of the form fields will automatically be the keys in the $_GET array):

Welcome <?php echo $_GET["fname"]; ?>.<br>
You are <?php echo $_GET["age"]; ?> years old!

When to use method="get"?

When using method="get" in HTML forms, all variable names and values are displayed in the URL.
Note: This method should not be used when sending passwords or other sensitive information!
However, because the variables are displayed in the URL, it is possible to bookmark the page. This can be useful in some cases.
Note: The get method is not suitable for very large variable values. It should not be used with values exceeding 2000 characters.

-------------------

In PHP, the predefined $_POST variable is used to collect values in a form with method="post".

The $_POST Variable

The predefined $_POST variable is used to collect values from a form sent with method="post".
Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.
Note: However, there is an 8 MB max size for the POST method, by default (can be changed by setting the post_max_size in the php.ini file).

Example

When the user clicks the "Submit" button, the URL will look like this:

http://www.w3schools.com/welcome.php

The "welcome.php" file can now use the $_POST variable to collect form data (the names of the form fields will automatically be the keys in the $_POST array):

Welcome <?php echo $_POST["fname"]; ?>!<br>
You are <?php echo $_POST["age"]; ?> years old.

When to use method="post"?

Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.
However, because the variables are not displayed in the URL, it is not possible to bookmark the page.

The PHP $_REQUEST Variable

The predefined $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE.
The $_REQUEST variable can be used to collect form data sent with both the GET and POST methods.

Example

Welcome <?php echo $_REQUEST["fname"]; ?>!<br>
You are <?php echo $_REQUEST["age"]; ?> years old.