C library function strspn()

C library function strspn()

#include <cstring>
#include <iostream>

using namespace std;

int main()
{
   char src[] = "0123456789";
   char dest[] = "190126abqs121kfew";

   size_t length = strspn(dest, src);

   cout << dest << " contains " << length << " initial numbers";
   return 0;
}

Output