The isspace() function tests for the standard white-space characters for which isalnum(3) is false. The standard white-space characters are the following:
‘ '
Space character.
\f
Form feed.
\n
New-line.
\r
Carriage return.
\t
Horizontal tab.
\v
And vertical tab.
In the ``C'' locale, isspace() returns true only for the standard white-space characters.
RETURN VALUES
The isspace() function returns zero if the character tests false and returns non-zero if the character tests true.
The isspace() function conforms to ANSI X3.159-1989 (“ANSI C”).
CAVEATS
The argument to isspace() must be EOF or representable as an unsigned char; otherwise, the behavior is undefined. See the CAVEATS section of ctype(3) for more details.