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isalnum, __iscsym, iswalnum, _ismbcalnum

Header File

ctype.h, mbstring.h

Category

Classification Routines

Prototype

int isalnum(int c);

int __iscsym(int c);

int iswalnum(wint_t c);

int _ismbcalnum(unsigned int c);

Description

Tests for an alphanumeric character.

isalnum is a macro that classifies ASCII-coded integer values by table lookup. The macro is affected by the current locale’s LC_CTYPE category. For the default C locale, c is a letter (A to Z or a to z) or a digit (0 to 9).

You can make this macro available as a function by undefining (#undef) it.

Return Value

It is a predicate returning nonzero for true and 0 for false.

isalnum returns nonzero if c is a letter or a digit.

__iscsym returns nonzero if c is a letter, underscore, or digit.

iswalnum returns nonzero if iswalpha or iswdigit return true for c.

_ismbcalnum returns true if and only if the argument c is a single-byte ASCII English letter.

Example

Copy Code

    #include <stdio.h>
    #include <ctype.h>
    int main(void)
    {
      char c = 'C';

      if (isalnum(c))
        printf("%c is alphanumeric\n",c);
      else
        printf("%c is not alphanumeric\n",c);
      return 0;
    }

Portability

| POSIX | Win32 | ANSI C | ANSI C++
isalnum | + | + | + | +
__iscsym |  | + |  |
_ismbcalnum |  | + |  |
iswalnum |  | + | + | +

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