std::basic_string::rfind

#include <string>
#include <iostream>

void print(std::string::size_type n, std::string const &s)
{
  if(n == std::string::npos)
    std::cout << "not found\n";
  else
    std::cout << "found: " << s.substr(n) << '\n';
}

int main()
{
  std::string::size_type n;
  std::string const s = "This is a string";

  // search backwards from beginning of string
  n = s.rfind("is");
  print(n, s);
  // search backwards from position 4
  n = s.rfind("is", 4);
  print(n, s);
  // find a single character
  n = s.rfind('s');
  print(n, s);
  // find a single character
  n = s.rfind('q');
  print(n, s);
}