How Can I Redirect C 's `cin` and `cout` to External Files?

Redirecting cin and cout to External Files

To redirect the input and output streams (cin and cout, respectively) to external files, follow these steps:

#include <iostream>
#include <fstream>

int main() {
    // Open input file for reading
    std::ifstream in("in.txt");
    // Save old input buffer
    std::streambuf *cinbuf = std::cin.rdbuf();
    // Redirect cin to input file
    std::cin.rdbuf(in.rdbuf());

    // Open output file for writing
    std::ofstream out("out.txt");
    // Save old output buffer
    std::streambuf *coutbuf = std::cout.rdbuf();
    // Redirect cout to output file
    std::cout.rdbuf(out.rdbuf());

From this point onward, any input read from std::cin will come from "in.txt," and any output written to std::cout will be written to "out.txt."

To redirect in a single line, use:

auto cinbuf = std::cin.rdbuf(in.rdbuf());

This sets std::cin's buffer to in.rdbuf() and returns the old buffer for later use. The same technique can be used for std::cout (or any other stream).

Finally, to restore the standard input and output, reset the buffers:

std::cin.rdbuf(cinbuf);
std::cout.rdbuf(coutbuf);

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