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ISBLANK(3) Library Functions Manual ISBLANK(3)

isblank, isblank_l
blank-space single-byte character test

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

The isblank() and isblank_l() functions test for blank-space characters. In the C locale, the complete list of blank-space characters is:
‘ ’
Space character.
Horizontal tab.
OpenBSD always uses the C locale for these functions, ignoring the global locale, the thread-specific locale, and the locale argument.

These functions return zero if the character tests false or non-zero if the character tests true.

On systems supporting non-ASCII single-byte character encodings, these functions may return non-zero for additional characters, and the results of isblank() may depend on the LC_CTYPE locale(1).

isalnum(3), isalpha(3), isascii(3), iscntrl(3), isdigit(3), isgraph(3), islower(3), isprint(3), ispunct(3), isspace(3), isupper(3), iswblank(3), isxdigit(3), stdio(3), toascii(3), tolower(3), toupper(3), ascii(7)

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

The isblank() function has been available since 4.4BSD, and isblank_l() since OpenBSD 6.2.

The argument c must be EOF or representable as an unsigned char; otherwise, the result is undefined.
September 5, 2017 OpenBSD-current