ISBLANK(3) Library Functions Manual ISBLANK(3)

isblank
blank-space character test

Standard C Library (libc, -lc)

#include <ctype.h>

int
isblank(int c);

The isblank() function tests for the standard blank-space characters. The standard blank-space characters are the following:

‘ ’
Space character.
Horizontal tab.

In the ``C'' locale, isblank() returns true only for the standard blank-space characters.

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

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

The argument to isblank() must be EOF or representable as an unsigned char; otherwise, the behavior is undefined. See the CAVEATS section of ctype(3) for more details.
April 17, 2008 NetBSD 9.0