#include <ctype.h> int isblank(int c);
This functions checks whether c, which must have the value of an unsigned char or EOF, falls into a certain character class according to the current locale.
isblank() checks for a blank character; that is, a space or a tab. This function is a GNU extension.
The values returned are nonzero if the character c falls into the tested class, and a zero value if not.
The details of what characters belong into which class depend on the current locale. For example, isupper() will not recognize an A - umlaut as an uppercase letter in the default C locale.