c++ std::string转大、小写

#include <iostream>
#include <algorithm>

int main()
{
  std::string src = "HELLO, WORLD!";
  std::string dst;

  std::transform(src.begin(), src.end(), std::back_inserter(dst), ::tolower);
  std::transform(src.begin(), src.end(), src.begin(), ::tolower);
}