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I am beginner in C++ and I have a question that is beyond my limits. I compile under GNU GCC. I use

#include<stdio.h>

also known as:

#include<cstdio>

At some point in my program I tell the program to use the file de_facut.txt as an in file:

freopen("de_facut.txt","r",stdin);

How can I tell the program to use the console to put the input (as default) instead of the in file? First I want to read from that file, but later in the program I want the user to enter input in the console. I hope you understood my problem, I am not very good at english.

the_young_programmer
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  • Why are you using `freopen` at all? In fact, why are you using C functions at all? This is C++! Use `std::cin` for your console input, and a `std::ifstream` for your file input. Nothing more complicated than that... – Lightness Races in Orbit Oct 31 '15 at 20:12
  • I don't want to use streams. I resolved my problem, read my comment for the other guy (if you want). – the_young_programmer Oct 31 '15 at 21:00
  • If you're learning C++ you should learn C++. It's up to you of course, but if you want to develop marketable skills then you might consider listening to the experts ;) – Lightness Races in Orbit Oct 31 '15 at 23:33

3 Answers3

4

Use fclose():

FILE *fp=freopen("data.txt","r",stdin);
/*your code here*/
fclose(fp);

ref: C library function - freopen()

Catoverflow
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3

The same question has been asked about stdout: How to redirect the output back to the screen after freopen("out.txt", "a", stdout), but the answer is the same for both - there's no clean way of doing this: http://c-faq.com/stdio/undofreopen.html

Since you do need to read from the console later in the program, I'd suggest you just open the file as, well, a file. If the reason you wanted to use stdin to read from a file is the convenience of not having to pass the file handle to functions like fscanf, you could consider using fstream facilities instead - the code can look exactly as when reading from the console:

#include <iostream>
#include <fstream>

using namespace std;
int main()
{
    int x;
    cin >> x; // reading from console
    {
        ifstream cin("input.txt");
        cin >> x; // reading from file
    }
    cin >> x; // again from console

    return 0;
}
Community
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AlphaStream
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  • I am afraid you didn't understand my question at all... Anyway thank you for the help, I resolved the problem myself... I use now global FILE * fin; and FILE * fout; and close the files where I need to read from console. – the_young_programmer Oct 31 '15 at 20:58
  • @the_young_programmer: Alpha understood the question perfectly. That you don't like the answer doesn't make it any less accurate. Also, if you found a solution, you should post it as an answer so that it may assist future readers. When you post a question here it is not just for you! – Lightness Races in Orbit Oct 31 '15 at 23:34
1

In windows, 

freopen("CON","r",stdin);

this code worked for me. It switches the stdin to console.
P.S: The text file used to take input before this, must be ended with a newline.

Risal Shahriar Shefin
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