C++ program compiling without functional header

Question

As per CPP Doc , std::greater is defined in <functional> header but my C++ program using std::greater is compiling with TDM-GCC-64 5.1.0 and running with only the following includes :

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <unordered_map>

It could be because <algorithm> automatically includes <functional> but since this is not mentioned in the doc, I was wondering is there a way to know this before hand ?

Answer 1

只是为了结束该主题，结论是这是依赖于实现的，并且应该包括所有必要的头部以便于移植。