Please review my strstr implementation. This is an interview question that say does not allow the use of strlen(). Is there a better way than using a boolean below?

#include <iostream>
#include <cstring>
char* my_strstr(char * s1, const char *s2)
{
  if ( s1 == NULL || s2 == NULL )
    return NULL;

  size_t s2Size = 0;

  const char *end = s2;
  while (*end++)
    ++s2Size;

  bool match;
  while ( *s1 )
  {
    match = true;
    for ( int i = 0; i < s2Size ; ++i )
    {
      if ( s1[i] != s2[i] )  
      {
        match = false;
        break;
      }
    }
    if ( match )
      return s1;

    ++s1;
  }
  return NULL;
}

const char* my_strstr(const char * s1, const char *s2)
{
  return my_strstr(const_cast<char*>(s1),s2);
}


int main()
{
  const char str[]= "This is a strstr test";
  const char search[]= "strstr";

  const char *result = my_strstr(str,search);

  if ( result )
    printf("original: %s\n item: %s\n found: %s\n", str, search, result );
}