Question

What’s the most efficient/safest way to check if a string in C is made up only of spaces? Do I need to write a function myself to check or is there one in string.h that I can use?

Answer 1

Well, writing your own is trivial:

int IsSpaces( char * s ) {

    while ( * s ) {
        if ( ! isspace( * s ) ) {
            return 0;
        }
        s++;
    }
    return 1;
}

Anything you use from the standard library is not likely to be much more efficient.