#include <stdio.h>

#include <string.h>

int main () {

   int len;

   const char str1[] = "ABCDEFG019874";

   const char str2[] = "ABCD";

​

   len = strspn(str1, str2);

​

   printf("Length of initial segment matching %d\n", len );

   return(0);

}

​