XI. Character Type Functions


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. 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 (inclusive) and 0 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.

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.


None besides functions from the standard C library which are always available.


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.

PHP 的 Windows 版本已经内置该扩展模块的支持。无需加载任何附加扩展库即可使用这些函数。

注: Builtin support for ctype is available with PHP 4.3.0.


本扩展模块在 php.ini 中未定义任何配置选项。





ctype_alnum -- Check for alphanumeric character(s)
ctype_alpha -- Check for alphabetic character(s)
ctype_cntrl -- Check for control character(s)
ctype_digit -- Check for numeric character(s)
ctype_graph -- Check for any printable character(s) except space
ctype_lower -- Check for lowercase character(s)
ctype_print -- Check for printable character(s)
ctype_punct --  Check for any printable character which is not whitespace or an alphanumeric character
ctype_space -- Check for whitespace character(s)
ctype_upper -- Check for uppercase character(s)
ctype_xdigit --  Check for character(s) representing a hexadecimal digit

add a note add a note User Contributed Notes
14-Oct-2006 10:44
In PHP versions before 4.4.1, ctype functions have a bug handling very large integers.
See Crimson's comment under ctype_digit, or this test code from the bug:
= 394829384;

Expected result:

Actual result:

The fix is to cast it as a string:
... or use a current version of PHP!
avarab at gmail dot com
03-Jan-2006 04:58
In case the ctype_*() functions aren't compiled in your PHP and you can't recompile for some reason (e.g. shared host) you can use the compatability functions from the MediaWiki project which use preg_* as a replacement[1], removing lines 2 and 3 in the source should make them suitable for usage elsewhere.

Shameless self-advertisement, but hey, we find them useful;)

1. A tinyurl because the submission script complained about long lines: http://tinyurl.com/7hz4l
1. The real url split up:
Gregory Boshoff
07-Aug-2005 11:47
As noted above unfortunately many PHP developers are seemingly unaware of these functions and are still using less  efficient equivalents.

Use the ctype functions for input type vaildation.

Example wrapper function:

 function detect_type($str, $type_req = ''){
       $type = array();
     (ctype_alnum($str) === TRUE) ? ($type = 'alnum') : FALSE;
     (ctype_digit($str) === TRUE) ? ($type = 'digit') : FALSE;
     (ctype_alpha($str) === TRUE) ? ($type = 'alpha') : FALSE;
       return ($type === $type_req) ? TRUE : FALSE;
   } // end fun

$str = 'AlphaString';
$type_req = 'alpha';

// Returns TRUE if the string is of the required type
echo detect_type($str, $type_req);