问题描述

如何将 cin 重定向到 in.txt 并将 cout 重定向到 out.txt?

How can I redirect cin to in.txt and cout to out.txt?

推荐答案

这是您想要执行的操作的示例.阅读注释以了解代码中每一行的作用.我已经在我的电脑上用 gcc 4.6.1 测试过它；它工作正常.

Here is an working example of what you want to do. Read the comments to know what each line in the code does. I've tested it on my pc with gcc 4.6.1; it works fine.

#include <iostream>
#include <fstream>
#include <string>

void f()
{
    std::string line;
    while(std::getline(std::cin, line))  //input from the file in.txt
    {
        std::cout << line << "
";   //output to the file out.txt
    }
}
int main()
{
    std::ifstream in("in.txt");
    std::streambuf *cinbuf = std::cin.rdbuf(); //save old buf
    std::cin.rdbuf(in.rdbuf()); //redirect std::cin to in.txt!

    std::ofstream out("out.txt");
    std::streambuf *coutbuf = std::cout.rdbuf(); //save old buf
    std::cout.rdbuf(out.rdbuf()); //redirect std::cout to out.txt!

    std::string word;
    std::cin >> word;           //input from the file in.txt
    std::cout << word << "  ";  //output to the file out.txt

    f(); //call function


    std::cin.rdbuf(cinbuf);   //reset to standard input again
    std::cout.rdbuf(coutbuf); //reset to standard output again

    std::cin >> word;   //input from the standard input
    std::cout << word;  //output to the standard input
}

您可以在一行中保存和重定向:

auto cinbuf = std::cin.rdbuf(in.rdbuf()); //save and redirect

此处 std::cin.rdbuf(in.rdbuf()) 将 std::cin's 缓冲区设置为 in.rdbuf()然后返回与 std::cin 关联的旧缓冲区.使用 std::cout 也可以做到同样的事情 —或任何流.

Here std::cin.rdbuf(in.rdbuf()) sets std::cin's buffer to in.rdbuf() and then returns the old buffer associated with std::cin. The very same can be done with std::cout — or any stream for that matter.

希望有所帮助.

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