The functions provided by this extension check whether a character or string falls into a certain character class according to the current locale (see also setlocale()).
When called with an integer argument these functions behave exactly like their C counterparts from ctype.h.
When called with a string argument they will check every character in the string and will only return TRUE if every character in the string matches the requested criteria. When called with an empty string the result will always be TRUE.
Passing anything else but a string or integer will return FALSE immediately.
Beginning with PHP 4.2.0 these functions are enabled by default. For older versions you have to configure and compile PHP with --enable-ctype. You can disable ctype support with --disable-ctype.
The windows version of PHP has built in support for this extension. You do not need to load any additional extension in order to use these functions.
Note: Builtin support for ctype is available with PHP 4.3.0.