diff between mysql_escape_string and mysql_real_escape_string

$item = "Zak's Laptop";
$a=mysql_connect('localhost','root','');
//$escaped_item = mysql_escape_string($item);
$escaped_item = mysql_real_escape_string($item);
echo $escaped_item;

?>
output :  Zak\'s Laptop
See the code above we use the server connection, in case of using the mysql_real_escape_string,
if you are not mention the server connection
i.e $a=mysql_connect('localhost','root','');
you may get the error below
Warning: mysql_real_escape_string(): Access denied for user 'ODBC'@'localhost' (using password: NO) in c:\program files\easyphp1-8\www\currentworking\bikes_adda\mysql.php on line 5

Warning: mysql_real_escape_string(): A link to the server could not be established in c:\program files\easyphp1-8\www\currentworking\bikes_adda\mysql.php on line 5

so before using  mysql_real_escape_string , use server connection.
BUT In case of mysql_escape_string , we noneed to use of server conncetion.
 just use the code normally...

$item = "Zak's Laptop";
$escaped_item = mysql_escape_string($item);
echo $escaped_item;
?>
output :  Zak\'s Laptop

Note: mysql_escape_string() does not escape % and _. 

mysql_real_escape_string

(PHP 4 >= 4.3.0, PHP 5)
mysql_real_escape_string -- Escapes special characters in a string for use in a SQL statement

Description

string mysql_real_escape_string ( string unescaped_string [, resource link_identifier] )

Escapes special characters in the unescaped_string, taking into account the current character set of the connection so that it is safe to place it in a mysql_query(). If binary data is to be inserted, this function must be used.
mysql_real_escape_string() calls MySQL's library function mysql_real_escape_string, which prepends backslashes to the following characters: \x00, \n, \r, \, ', " and \x1a.
This function must always (with few exceptions) be used to make data safe before sending a query to MySQL.

Parameters

unescaped_string

The string that is to be escaped.

link_identifier

The MySQL connection. If the link identifier is not specified, the last link opened by mysql_connect() is assumed. If no such link is found, it will try to create one as if mysql_connect() was called with no arguments. If by chance no connection is found or established, an E_WARNING level warning is generated.

Return Values

Returns the escaped string, or FALSE on error.

Examples

Example 1. Simple mysql_real_escape_string() example // Connect $link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')     OR die(mysql_error()); // Query $query = sprintf("SELECT * FROM users WHERE user='%s' AND password='%s'",             mysql_real_escape_string($user),             mysql_real_escape_string($password)); ?>

Example 2. An example SQL Injection Attack // Query database to check if there are any matching users $query = "SELECT * FROM users WHERE user='{$_POST['username']}' AND password='{$_POST['password']}'"; mysql_query($query); // We didn't check $_POST['password'], it could be anything the user wanted! For example: $_POST['username'] = 'aidan'; $_POST['password'] = "' OR ''='"; // This means the query sent to MySQL would be: echo $query; ?> The query sent to MySQL: SELECT * FROM users WHERE user='aidan' AND password='' OR ''='' This would allow anyone to log in without a valid password.

Example 3. A "Best Practice" query Using mysql_real_escape_string() around each variable prevents SQL Injection. This example demonstrates the "best practice" method for querying a database, independent of the Magic Quotes setting. // Quote variable to make safe function quote_smart($value) {     // Stripslashes     if (get_magic_quotes_gpc()) {         $value = stripslashes($value);     }     // Quote if not a number or a numeric string     if (!is_numeric($value)) {         $value = "'" . mysql_real_escape_string($value) . "'";     }     return $value; } // Connect $link = mysql_connect('mysql_host', 'mysql_user', 'mysql_password')     OR die(mysql_error()); // Make a safe query $query = sprintf("SELECT * FROM users WHERE user=%s AND password=%s",             quote_smart($_POST['username']),             quote_smart($_POST['password'])); mysql_query($query); ?> The query will now execute correctly, and SQL Injection attacks will not work.

Notes

Note: A MySQL connection is required before using mysql_real_escape_string() otherwise an error of level E_WARNING is generated, and FALSE is returned. If link_identifier isn't defined, the last MySQL connection is used.

Note: If magic_quotes_gpc is enabled, first apply stripslashes() to the data. Using this function on data which has already been escaped will escape the data twice.

Note: If this function is not used to escape data, the query is vulnerable to SQL Injection Attacks.

Note: mysql_real_escape_string() does not escape % and _. These are wildcards in MySQL if combined with LIKE, GRANT, or REVOKE.