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### 3.4 `isblank`, `isblank_l`—blank character predicate

Synopsis

    #include <ctype.h>
    int isblank(int c);

    #include <ctype.h>
    int isblank_l(int c, locale_t locale);

Description
`isblank` is a function which classifies singlebyte charset values by table lookup. It is a predicate returning non-zero for blank characters, and 0 for other characters. It is defined only if c is representable as an unsigned char or if c is EOF.

`isblank_l` is like `isblank` but performs the check based on the locale specified by the locale object locale. If locale is LC_GLOBAL_LOCALE or not a valid locale object, the behaviour is undefined.

Returns
`isblank`, `isblank_l` return non-zero if c is a blank character.

Portability
`isblank` is C99. `isblank_l` is POSIX-1.2008.

No supporting OS subroutines are required.