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Manual Pages  — ISBLANK


isblank – space or tab character test



Standard C Library (libc, -lc)


#include <ctype.h>

isblank(int c);

isblank_l(int c, locale_t loc);


The isblank() function tests for a space or tab character. For any locale, this includes the following standard characters:

"\t "

In the "C" locale, a successful isblank() test is limited to these characters only. The value of the argument must be representable as an unsigned char or the value of EOF.

The isblank_l() function takes an explicit locale argument, whereas the isblank() function uses the current global or per-thread locale.


The isblank() function returns zero if the character tests false and returns non-zero if the character tests true.


The BSD 4.4 extension of accepting arguments outside of the range of the unsigned char type in locales with large character sets is considered obsolete and may not be supported in future releases. The iswblank() function should be used instead.


ctype(3), iswblank(3), xlocale(3), ascii(7)


The isblank() function conforms to ISO/IEC 9899:1999 ("ISO C99"). The isblank_l() function conforms to IEEE Std 1003.1-2008 ("POSIX.1").

ISBLANK (3) July 17, 2005

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