FOR MAMP
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
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
