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
It means that if you pass an integer smaller than 256 it will use the
ASCII value of it to see if it fits in the specified range (digits are in
0x30-0x39). If the number is between -128 and -1 inclusive then 256 will
be added and the check will be done on that.
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 in PHP < 5.1 and FALSE since 5.1.
Passing anything else but a string or integer will
return FALSE immediately.
It should be noted that ctype functions are always preferred over
regular expressions, and even to some equivalent str_* and is_* functions.
This is because of the fact that ctype uses a native C library and thus
processes significantly faster.
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.
Builtin support for ctype is available with PHP 4.3.0.