为什么fclose(stdin);或freopen("CON","w",stdin);关不掉文件输入：

//-std=c++14
#include<bits/stdc++.h>
signed main(){
	int x;
	freopen("C:\\Users\\Administrator\\Desktop\\in.txt","r",stdin);
	std::cin>>x;
	std::cout<<x<<'\n';
	fclose(stdin);
	//freopen("CON","w",stdin);
	std::cin>>x;
	std::cout<<x<<'\n';
	return 0;
}#include<bits/stdc++.h>
signed main(){
	int x;
	freopen("C:\\Users\\Administrator\\Desktop\\in.txt","r",stdin);
	std::cin>>x;
	std::cout<<x<<'\n';
	fclose(stdin);
	//freopen("CON","w",stdin);
	std::cin>>x;
	std::cout<<x<<'\n';
	return 0;
}

in.txt：
123
无输入
输出：
123
123