C++ file-redirection

Question

For faster input, I read that you can do file-redirection and include a file with the cin inputs already set.

In theory it should be used like following:

App.exe inputfile outputfile

As far as I understood from C++ Primer book, The following C++ code[1] should be reading cin input from the text file and shouldn't need to any other special indication like[2]

[2]

include <fstream>
ofstream myfile;
myfile.open ();

[1] The following C++ code...

#include <iostream>
int main()
{
    int val;
    std::cin >> val; //this value should be read automatically for inputfile
    std::cout << val;
    return 0;
}

Am I missing something?

Answer 1

To use your code [1] you have to call your program like this:

App.exe < inputfile > outputfile

You can also use:

App.exe < inputfile >> outputfile

In this case the output wouldn't be rewritten with every run of the command, but output will be appended to already existing file.

More information about redirecting input and output in Windows you can find here.

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Note that the <, > and >> symbols are to be entered verbatim — they are not just for presentation purposes in this explanation. So, for example:

App.exe < file1 >> file2