[SOLVED] Attach console to GUI application on Windows

T3STY

I was looking at this article:
https://justcheckingonall.wordpress.com/2008/08/29/console-window-win32-app/
which explains how to attach a console to a Win32/GUI application.

I was wondering if there was a more Qt-like way of doing this? I would love a console in debug mode. Also, if the console was interactive (like, I could type commands while the GUI is still running) it would be awesome; but I doubt this is possible...

EDIT
As an alternative solution, would it be possible to use some GUI widgets from Qt to actually run console commands just like I would do from the Windows console (cmd.exe) ?

alex_malyu

If you want console just to display output in debug configuration you can simply specify that application is in the console application.
http://doc.qt.io/qt-4.8/qmake-common-projects.html

T3STY

The console CONFIG option does not do the trick. It all depends on whether you're creating a QCoreApplication or QApplication to create console or GUI -based applications; but not both at the same time.

T3STY

previous reply text removed as it's useless, read next

Re-EDIT
The solution was far simpler than I thought... AllocConsole() creates a new console; AttachConsole() will link the new console to the application; then it's just a matter of redirecting I/O to the new console by reopening the std streams...

#include <QApplication>
#include <QWidget>

#define DEBUG

#ifdef DEBUG
    #include <windows.h>
    #include <stdio.h>
#endif

int main(int argc, char *argv[]){
#ifdef DEBUG
    // detach from the current console window
    // if launched from a console window, that will still run waiting for the new console (below) to close
    // it is useful to detach from Qt Creator's <Application output> panel
    FreeConsole();

    // create a separate new console window
    AllocConsole();

    // attach the new console to this application's process
    AttachConsole(GetCurrentProcessId());

    // reopen the std I/O streams to redirect I/O to the new console
    freopen("CON", "w", stdout);
    freopen("CON", "w", stderr);
    freopen("CON", "r", stdin);
#endif

    puts("creating QApplication");
    QApplication app(argc, argv);

    puts("creating QWidget");
    QWidget w;
    puts("showing widget");
    w.show();
    puts("type something:");
    getchar();
    w.resize(320, 240);
    puts("yeeeey! It works!");

    app.exec();

    return 0;
}

Wherever the application is launched from now it will open it's own console window and use that for I/O. Please note that this is the naive way, I didn't make checks for possible failures, so you should add them for a fail-safe application.
So that's it, sorry for opening a thread and eventually answering the quesiton myself. I hope it'll be useful to others as well ;)

VRHans

@T3STY said:

freopen("CON", "w", stdout);
freopen("CON", "w", stderr);
freopen("CON", "r", stdin);

Thanks for this! I'd been trying to do this the 'Windows way' and never actually seeing the output - but replacing my _open_osfhandle approach with the simple one above fixed it for me. Lifesaver! Cheers.

JimboStlawrence

@T3STY Thank you! First time in trying QT; I have downloaded someones kind demo of compute shaders to try to get to grips working on the GPu, finally got it compiling, but for learning, a debug window is essential!!!

JonB

@JimboStlawrence
Are you aware that if you run your Qt GUI app from Qt Creator debugger you automatically get a console window there anyway?