c++ 从文件获取输入

实例1：

#include <iostream>#include <fstream>using namespace std;int main(){ifstream cin("in.txt");ofstream cout("out.txt");int a,b;cin>>a>>b;cout<<a+b<<endl;return 0;}

实例2：

#include <iostream>#include <fstream>#include <cstdio>using namespace std;int main(){freopen("in.txt","r",stdin);freopen("out.txt","w",stdout);int a,b;cin>>a>>b;cout<<a+b<<endl;return 0;}