How to Display Console Output in a Native C Windows Program?

Displaying Console Output in Native C Windows Program

In C Windows programs using the WinMain entry point, console output generated by functions like std::cout may not be visible by default. This is because graphical user interface (GUI) applications typically do not have a console window associated with them.

Solutions:

1. Attach a Console to the Application:

• Utilize the AllocConsole() function to create a new console window for your program.
• Redirect standard input (STDIN), output (STDOUT), and error (STDERR) streams to the new console using functions like _open_osfhandle() and _fdopen().

2. Redirect Console Output to a File:

• If you cannot modify the codebase, you can still view console output by redirecting it to a text file.
• Use the FreeConsole() function to release the console handle.
• Call OutputDebugString() to redirect output to the file, which can be viewed using a debugging tool like DebugView.

Example Code Using Console Redirection:

The following code snippet demonstrates how to attach a console to a Windows program and redirect streams to it:

void RedirectIOToConsole()
{
    int hConHandle;
    long lStdHandle;
    CONSOLE_SCREEN_BUFFER_INFO coninfo;
    FILE *fp;

    // Allocate a console for this app
    AllocConsole();

    // Set the screen buffer size for scrolling
    GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &coninfo);
    coninfo.dwSize.Y = 500;
    SetConsoleScreenBufferSize(GetStdHandle(STD_OUTPUT_HANDLE), coninfo.dwSize);

    // Redirect stdout
    lStdHandle = (long)GetStdHandle(STD_OUTPUT_HANDLE);
    hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);
    fp = _fdopen(hConHandle, "w");
    *stdout = *fp;
    setvbuf(stdout, NULL, _IONBF, 0);

    // Redirect stdin
    lStdHandle = (long)GetStdHandle(STD_INPUT_HANDLE);
    hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);
    fp = _fdopen(hConHandle, "r");
    *stdin = *fp;
    setvbuf(stdin, NULL, _IONBF, 0);

    // Redirect stderr
    lStdHandle = (long)GetStdHandle(STD_ERROR_HANDLE);
    hConHandle = _open_osfhandle(lStdHandle, _O_TEXT);
    fp = _fdopen(hConHandle, "w");
    *stderr = *fp;
    setvbuf(stderr, NULL, _IONBF, 0);
}

Include Header:

#include "guicon.h"

Usage:

#ifdef _DEBUG
    RedirectIOToConsole();
#endif

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