#include <iostream.h>

char *match(char *s1, char * s2)
{   while ( *s1 == *s2++ )
        if ( *s1++ == '=') return(s2);   // field delimiter 
    if (*s1 == '\0' && *(s2-1) == '=')
        return(s2);                      // match found     
    return(NULL);
}

char aa[] = "foo=abcdefg";

int main()
{    char *s = match("foo", aa);
     cout << s << endl;
}