Detecting if a string is just made up of spaces?

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 st开发者_如何学Pythonring.h that I can use?

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.

Try this:

if (!s[strspn(s, " ")]) /* it's all spaces */

If you want to also include tabs, newlines, etc. in your definition of "spaces", simply add them to the second argument of strspn.

man string.h brought me to the following manpage.

NAME strspn, strcspn - search a string for a set of characters

SYNOPSIS

   #include <string.h>

   size_t strspn(const char *s, const char *accept);

   size_t strcspn(const char *s, const char *reject);

DESCRIPTION

• The strspn() function calculates the length of the initial segment of s which consists entirely of characters in accept.

• The strcspn() function calculates the length of the initial segment of s which consists entirely of characters not in reject.

When you say space, do you mean exactly or a spacing character?

However, there is no such function, this works though:

int isonlyspaces(char *str) {
    while (*str++ == ' ');
    return --str == '\0';
}

If you mean spacing characters instead of a literal space, this version is appropriate:

int isonlyspaces(char *str) {
    while (isspace(*str++));
    return --str == '\0';
}