Like strpbrk, one use for find_first_of is finding whitespace in a string; space, tab, and newline are all whitespace characters.Example
int main() {
const char* WS = "\t\n ";
const int n_WS = strlen(WS);
char* s1 = "This sentence contains five words.";
char* s2 = "OneWord";
char* end1 = find_first_of(s1, s1 + strlen(s1), WS, WS + n_WS);
char* end2 = find_first_of(s2, s2 + strlen(s2), WS, WS + n_WS);
printf("First word of s1: %.*s\n", end1 – s1, s1);
printf("First word of s2: %.*s\n", end2 – s2, s2);
}