please explain your codes

* Returns the length of the initial portion of str1 which consists only of characters that are part of str2. * The search does not include the terminating null-characters of either strings, but ends there. * * Example, string Span("abcdefgh", "abXXcdeZZh"); // returns 5 * * ALLOWED: Pointer operators: *, & Binary integer operators: -, +, *, ==, !=, Unary integer operators: ! Shorthand operators based on the above: ex. >, ^, /, % Unary integer operators: ~, * * int stringSpan(char * stri, char * str2) { // Your code here return 2; }