为什么cin/cout比scanf/printf慢

问题描述

#include <iostream>
using namespace std;

int main(){
    int t;
    long long int n,res,x;
    scanf("%d",&t);
    while(t--){
            scanf("%lld",&n);
            res=0;


    for(int i=0;i<n;i++){
            scanf("%lld",&x);
            res^=x;
    }
    if(res==0)
        printf("-1\n");
    else
        printf("%lld\n",res);

}
return 0;
}

当我使用cin和cout时，同一程序在hackerearth中超时.但是通过scanf和printf传递.

this same program when i used cin and cout was timed out in hackerearth. But passed with scanf and printf.

推荐答案

速度差异很大程度上归因于iostream I/O功能与C I/O功能保持同步.我们可以通过调用 std :: ios :: sync_with_stdio(false);

The speed difference is largely due to the iostream I/O functions maintaining synchronization with the C I/O functions. We can turn this off with a call to std::ios::sync_with_stdio(false);

默认情况下，每次输入/输出操作后，默认的标准C ++流都将同步到标准C流.

By default standard C++ streams are synchronized to the standard C stream after each input/output operation.

关闭同步后，C ++标准流将被允许独立缓冲其I/O，您可以尝试看看所花费的时间几乎相同(可能比scanf短)

Once synchronization is turned off, the C++ standard streams are allowed to buffer their I/O independently, you can try and see the time taken will be almost similar (possibly lesser than scanf)

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