Qt Creator cannot Auto-Complete Standard C++

Today I met a question. When I use std::map in my Qt project, I found Qt Creator can not auto-compelete functions.

This is my code:

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <iterator>
#include <map>
using namespace std;

......
    using mymap = map<string, vector<string> >;
    mymap m;
    for(mymap::iterator it=m.begin();
        it!=m.end(); it++){
        string item = it->first;
    }
......

In this code block, the ->first is code by myself. When I code it complete, Qt Creator cannot show all functions even ->. How to solve the problem? Can you help me?

I use Qt5.7.0 with Mingw5.3.0, and my Qt Creator version is 4.11.0.