how to find the the length of a string in c++ code example

Example 1: length of string c++

// string::length
#include <iostream>
#include <string>

int main ()
{
  std::string str ("Test string");
  std::cout << "The size of str is " << str.length() << " bytes.\n";
  return 0;
}

Example 2: is it len function is aviable for c+=

str.length();