I can assign double to string?

Question

According to this page, there are five ways to assign something to a string:

          string (1) string& operator= (const string& str);
        c-string (2) string& operator= (const char* s);
       character (3) string& operator= (char c);
initializer list (4) string& operator= (initializer_list<char> il);
            move (5) string& operator= (string&& str) noexcept;

Then why could I compile the text below? Which of this options was used by compiler?

#include <iostream>
#include <string>

int main()
{
  std::string s;
  double d = 1.0;
  s = d; 
  std::cout << s << std::endl; 
}

And this is not just a senseless question - I've spent long hours trying to find this s = d assignment in my code. It should have been s = std::to_string(d) of course.

Compiler: GCC 4.8.4.

Answer 1

Your code is equivalent to this code:

#include <iostream>
#include <string>

int main()
{
  std::string s;
  double d = 1.0;
  char j = d;
  s = j; 
  std::cout << s << std::endl; 
}

So you will output a \1 followed by a line ending.

If you're using G++, specify -Wconversion to catch things like this.

f.cpp: In function ‘int main()’:
f.cpp:8:7: warning: conversion to ‘char’ from ‘double’ may alter its value [-Wfloat-conversion]
s = d;