strspn() function in C

The strspn() function returns the length of the initial substring of the string pointed to by str1 that is made up of only those character contained in the string pointed to by str2.

Syntax :

size_t strspn(const char *str1, const char *str2)
str1 : string to be scanned.
str2 : string containing the 
characters to match.
Return Value : This function
returns the number of characters
in the initial segment of str1 
which consist only of characters 
from str2.

// C program to illustrate strspn() function
#include <stdio.h>
#include <string.h>

int main () {
   int len = strspn("geeks for geeks","geek");
   printf("Length of initial segment matching : %d\n", len );
   return(0);
}

Output:

Length of initial segment matching 4

// C program to illustrate strspn() function
#include <stdio.h>
#include <string.h>

int main () {
   int len = strspn("i am","xyz");
   printf("Length of initial segment matching : %d\n", len );
   return(0);
}

Output:

Length of initial segment matching 0