I/O Redirection

  • Many programs take input from the console (stdin) and print output to the console (stdout and stderr). For example, consider this simple program that asks the user for a name and then greets the user:

    #include <iostream>
    using namespace std;
    int main() {
        cout << "Name: ";
        string name;
        getline(cin, name);
        cout << "Hello, " << name << "!" << endl;
  • In Terminal, we can compile and run this program with


    We would have to type input ourselves and we would see the output in the console:

    Name: Maxim
    Hello, Maxim!
  • However, we sometimes want our program to read input from a file instead of the console. In Terminal, we would execute something like this to use the contents of input.txt as input:

    ./hello < input.txt
  • Similarly, we can redirect output of the program so some file, such as output.txt:

    ./hello > output.txt

    After executing this command, output.txt will contain the output of the program. This file will be overwritten if it already exists or created if it does not exist.

  • We can also combine input and output redirection in Terminal with

    ./hello < input.txt > output.txt

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