php - mysql_real_escape_string is undefined

Question

I am using PHP version 5.3 and trying to use mysql_real_escape_string($unescaped_string) in my code, but I get the error:

Fatal error: Call to undefined function mysql_real_escape_string() 
in /var/www/engine/database.php on line 38

I can still connect to the database however. Why is it not available?

I am using PHP version 5.3.

Answer 1

Update as mentioned in comment, mysql_ has been deprecated since 5.5:

The mysql extension has been deprecated since PHP 5.5. The mysqli or PDO extension should be used instead. The deprecation has been decided in mysql_deprecation, where a discussion of the reasons behind this decision can be found.

and removed in PHP 7.

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mysql_real_escape_string() is standard part of MySQL function "batch" and should always work if the extension is loaded correctly.

Does any another mysql_ function work? (It should not)

Make sure, that you have this line uncommented in your php.ini:

extension=mysql.so

Also it'd be wise to use mysqli or PDO instead (mysql_ is deprecated), they both can take care of escaping for you.