Joomla! Documentation™

Warning!

For MAMP

Steps:

• Go to MAMP application >> Preferences (button) >> PHP (tab) >> Choose 5.3.1 or greater >> choose OK.
• Go to the MAMP folder >> bin >> php >> php5.3.26 >> conf >> edit php.ini >> add "magic_quotes_gpc = Off" a few lines above "magic_quotes_sybase = Off".
• Restart MAMP's servers.

For Most Mainstream Hosting Companies Running a CGI-Webinterface

Steps:

• Create a php.ini or php5.ini file with the following:

magic_quotes_gpc = Off

• Put it in your Joomla 3 root. Then change the htaccess.txt in your Joomla 3 root to .htaccess. Add the following lines to the .htaccess file (at the top), don't forget to change php.ini to php5.ini when applicable :

<IfModule mod_suphp.c>
  suPHP_ConfigPath /home/myusername/public_html/yourJ3folder
  <Files php.ini>
    order allow,deny
    deny from all
  </Files>
</IfModule>

Change "myusername" and "yourJ3folder" to your respective folders. The "/home/myusername/public_html/yourJ3folder" can be found via the Global Configuration:

In Joomla Backend > System > System Information > [Directory Permissions], the folder is usually the same as the log directory (but without /logs at the end).

.htaccess for Some Hosts

For some hosts, add the following to the .htaccess file in the root of your site (for example /home/myusername/public_html/.htaccess)

php_flag magic_quotes_gpc off

Yet Another Solution For Shared Hosts

• create a php.ini file at your Joomla! root.
• Add this content to the file and save

magic_quotes_gpc = Off
magic_quotes_runtime = Off
magic_quotes_sybase = Off

• Edit your .htaccess file and add this line at the top and save the file

SetEnv PHPRC /home/youruser/public_html/php.ini

• Test if the error message goes away

source : http://stackoverflow.com/questions/517008/how-to-turn-off-magic-quotes-on-shared-hosting

Another Solution (for the Hosts Where PHP is Running as FCGI Module)

Works for PHP 5.3 and higher

• create a .user.ini file at your Joomla! root.
• Add this content to the file and save

magic_quotes_gpc = Off