当我将int添加到char（'a'+ 1）时调用哪个operator +函数

I've following code:

我遵循以下代码:

#include <iostream>
using namespace std;

int main()
{
  cout << ('a' + 1) << endl;
  cout << static_cast<char>('a' + 1) << endl;
  cout << static_cast<int>('a' + 1) << endl;
}
#include <ios