Создать аналог функции strpbrk на С++

#include <string.h>
#include <stdio.h>
 
int main( void )
{
   char string[100] = "The 3 men and 2 boys ate 5 pigs\n";
   char *result = NULL;
 
   // Return pointer to first digit in "string".
   printf( "1: %s\n", string );
   result = strpbrk( string, "0123456789" );
   printf( "2: %s\n", result++ );
   result = strpbrk( result, "0123456789" );
   printf( "3: %s\n", result++ );
   result = strpbrk( result, "0123456789" );
   printf( "4: %s\n", result );
}

#include <cstring>
#include <iostream>
 
const char* strpbrk(const char* s1, const char* s2)
{
    std::size_t s1len = std::strlen(s1);
    std::size_t s2len = std::strlen(s2);
    for (int i = 0; i < s1len; i++)
        for (int j = 0; j < s2len; j++)
            if (s1[i] == s2[j])
                return &s1[i];
    return nullptr;
}
 
int main() 
{
    char string[100] = "The 3 men and 2 boys ate 5 pigs\n";
    char *result = nullptr;
    std::cout << "1: " << string << std::endl;
    result = strpbrk(string, "0123456789");
    std::cout << "2: " << (result++) << std::endl;
    result = strpbrk(result, "0123456789");
    std::cout << "3: " << (result++) << std::endl;
    result = strpbrk(result, "0123456789");
    std::cout << "4: " << result << std::endl;
    return 0;
}