C++输入为文件

#include <iostream>
using namespace std;
int main()
{
	freeopen("c:\\tmp\\test.txt","r",stdin);
	//此后所有输入都来自文件 c:\tmp\test.txt 
	int n, max = 0;
	while(cin >> n)
	{
		if(n > max) max = n;
	}
	printf("%d", max);
	return 0;
}