Output to console from a Win32 GUI application on Windows 10

Question

I tried this code to output to the console:

#include <Windows.h>

#include <stdio.h>
#include <io.h>
#include <fcntl.h>

int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
    AllocConsole();

    HANDLE handle_out = GetStdHandle(STD_OUTPUT_HANDLE);
    int hCrt = _open_osfhandle((long) handle_out, _O_TEXT);
    FILE* hf_out = _fdopen(hCrt, "w");
    setvbuf(hf_out, NULL, _IONBF, 1);
    *stdout = *hf_out;

    HANDLE handle_in = GetStdHandle(STD_INPUT_HANDLE);
    hCrt = _open_osfhandle((long) handle_in, _O_TEXT);
    FILE* hf_in = _fdopen(hCrt, "r");
    setvbuf(hf_in, NULL, _IONBF, 128);
    *stdin = *hf_in;

    printf("Hello!");
}

the console opens but nothing is outputted to it. What's wrong with that code?

I tried all these suggestions:

https://justcheckingonall.wordpress.com/2008/08/29/console-window-win32-app/

http://dslweb.nwnexus.com/~ast/dload/guicon.htm

How do I print to the debug output window in a Win32 app?

but I couldn't get any output to the console created with AllocConsole() on Windows 10 in WinMain. Note: I actually didn't create any real Window. Was something changed in Window 10 that prevents the above solutions from working or is there something that I might be missing (compiler flags or something)?

What do you think?

Please don't ask your question in off site links. Please show the code that you tried. What you expected to happen, and what did happen. As it stands this question is off topic. — David Heffernan, Aug 24 '15 at 15:06
An when I do that I'll get 50 answers already this was answered already [duplicate]. — Zingam, Aug 24 '15 at 15:09
Why do you truncate your handles? A `long` on Windows is not large enough to store an `intptr_t` value. — IInspectable, Aug 24 '15 at 15:51
@IInspectable Criticism accepted but it didn't make a difference - it wouldn't work. — Zingam, Aug 24 '15 at 19:57
possible duplicate of [Redirecting cout to a console in windows](http://stackoverflow.com/questions/311955/redirecting-cout-to-a-console-in-windows) — Abhineet, Aug 25 '15 at 05:27

Zingam · Accepted Answer · 2015-08-25T06:00:48.673

Based on the accepted answer from ProXicT link with a few modifications. The following code works for std::cout. The other methods won't work on 64bit with Visual Studio 2015:

#include <iostream>
#include <cstdio>
#include <fstream>

#include <Windows.h>


// For debugging
#include <io.h>
#include <fcntl.h>


#define UNUSED(x) (void)(x)       // Unused param (C compatible - not applicable to expressions)

class outbuf : public std::streambuf {
public:
    outbuf() {
        setp(0, 0);
    }

    virtual int_type overflow(int_type c = traits_type::eof()) {
        return fputc(c, stdout) == EOF ? traits_type::eof() : c;
    }
};

int CALLBACK
WinMain (HINSTANCE hInstance,
         HINSTANCE /*hPrevInst*/, // Unused param (C++ only)
         LPSTR lpCmdLine,
         int (nShowCmd))
{
    UNUSED(hInstance);
//    UNUSED(hPrevInst);
    UNUSED(lpCmdLine);
    UNUSED(nShowCmd); // This param is used


    // create the console
    if (AllocConsole()) {
        FILE* pCout;
        freopen_s(&pCout, "CONOUT$", "w", stdout);
        SetConsoleTitle(L"Debug Console");
        SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_RED);
    }

    // set std::cout to use my custom streambuf
    outbuf ob;
    std::streambuf *sb = std::cout.rdbuf(&ob);

    // do some work here
    printf("Hello!\n");

    std::cout << "nShowCmd = " << nShowCmd << std::endl;
    std::cout << "Now making my first Windows window!" << std::endl;


    // make sure to restore the original so we don't get a crash on close!
    std::cout.rdbuf(sb);

    MessageBoxW (NULL,
                 L"Hello World!",
                 L"hello",
                 MB_OK | MB_ICONINFORMATION);

    return 0;
}

EDIT:

The same stuff as above but with colors for completeness:

#include <iostream>
#include <cstdio>
#include <fstream>

#include <Windows.h>


// For debugging
#include <io.h>
#include <fcntl.h>


#define UNUSED(x) (void)(x)       // Unused param (C compatible - not applicable to expressions)

class outbuf : public std::streambuf {
public:
    outbuf() {
        setp(0, 0);
    }

    virtual int_type overflow(int_type c = traits_type::eof()) {
        return fputc(c, stdout) == EOF ? traits_type::eof() : c;
    }
};

int CALLBACK
WinMain (HINSTANCE hInstance,
         HINSTANCE /*hPrevInst*/, // Unused param (C++ only)
         LPSTR lpCmdLine,
         int (nShowCmd))
{
    UNUSED(hInstance);
//    UNUSED(hPrevInst);
    UNUSED(lpCmdLine);
    UNUSED(nShowCmd); // This param is used


    // create the console
    if (AllocConsole()) {
        FILE* pCout;
        freopen_s(&pCout, "CONOUT$", "w", stdout);
        SetConsoleTitle(L"Debug Console");

    }

    // set std::cout to use my custom streambuf
    outbuf ob;
    std::streambuf *sb = std::cout.rdbuf(&ob);

    // do some work here

    printf("Hello!\n");

    HANDLE stdHandle = GetStdHandle(STD_OUTPUT_HANDLE);
    CONSOLE_SCREEN_BUFFER_INFO consoleInfo;
    WORD defaultConsoleTextAttributes;
    GetConsoleScreenBufferInfo(stdHandle, &consoleInfo);
    defaultConsoleTextAttributes = consoleInfo.wAttributes;
    WORD currentConsoleTextAttributes = FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_RED;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "nShowCmd = " << nShowCmd << std::endl;
    currentConsoleTextAttributes = FOREGROUND_GREEN;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_GREEN | FOREGROUND_INTENSITY;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_BLUE;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_BLUE | FOREGROUND_INTENSITY;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_RED;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_RED | FOREGROUND_INTENSITY;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_GREEN | FOREGROUND_BLUE;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_GREEN | FOREGROUND_BLUE | FOREGROUND_INTENSITY;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_GREEN | FOREGROUND_RED;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_GREEN | FOREGROUND_RED | FOREGROUND_INTENSITY;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_BLUE | FOREGROUND_RED;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;
    currentConsoleTextAttributes = FOREGROUND_BLUE | FOREGROUND_RED | FOREGROUND_INTENSITY;
    SetConsoleTextAttribute(stdHandle, currentConsoleTextAttributes);
    std::cout << "Now making my first Windows window!" << std::endl;



    // make sure to restore the original so we don't get a crash on close!
    std::cout.rdbuf(sb);

    Sleep(5000);
    ShowWindow(GetConsoleWindow(), SW_HIDE);
    FreeConsole();

    MessageBoxW (NULL,
                 L"Hello World!",
                 L"hello",
                 MB_OK | MB_ICONINFORMATION);

    return 0;
}

All that remains now is to make it into a complete logging class.

score 7 · Answer 2 · answered Nov 14 '15 at 18:58

7

Try this code.

AllocConsole();
HANDLE stdHandle;
int hConsole;
FILE* fp;
stdHandle = GetStdHandle(STD_OUTPUT_HANDLE);
hConsole = _open_osfhandle( (long)stdHandle, _O_TEXT);
fp = _fdopen(hConsole, "w");

freopen_s( &fp, "CONOUT$", "w", stdout);

printf("Hello console on\n");
std::cout << "Windows 10" << std::endl;

answered Nov 14 '15 at 18:58

Atori

113
2
6

2

Note: `#include ` and `#include ` required for the `_open_osfhandle` call – M.M Aug 10 '17 at 23:52
The first parameter of freopen_s is an out parameter, you can remove the previous three lines of code. – LLucasAlday Apr 11 '19 at 18:50

score 2 · Answer 3 · answered Sep 03 '17 at 03:05

2

If you're using g++, and you want your application to always have both a console and a GUI, then you can supply linker flags of both -mconsole and -mwindows to achieve this.

See this answer for more detail.

answered Sep 03 '17 at 03:05

M.M

138,810
21
208
365

Output to console from a Win32 GUI application on Windows 10

3 Answers3

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