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Posted 17 Jun 2000

Creating a console for your MFC app's debug output

, 17 Jun 2000
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How to send debugging output to a console in a MFC application
  • Download demo project - 12 Kb
  • Sample Image - MFCConsole.gif

    It's simply a matter of three function calls to print a message to a console in your MFC application. There are several reasons why you might want to send your debugging output to a console. Mine were, that 1st, I didn't have an IDE on the PC where I tested the debug-builds of my app and 2nd, the Mainframe was not always visible, which made matters worse.

    A last word of warning beforehand: Closing the console window will exit your application! Let's go:

    Creating the console

    To create a console window you need to call AllocConsole(). This function does not take any parameters and returns a BOOL, indicating whether the console has been created or not. You should create the console sometime in the beginning of your code. In the sample I've put the code into the CWinApp::OnInitInstance() override. Like this:
    BOOL CSmplConsoleApp::InitInstance()
    	// details omitted
    	// allocate a console
    #ifdef _DEBUG
    	if (!AllocConsole())
    		AfxMessageBox("Failed to create the console!", MB_ICONEXCLAMATION);
    	return TRUE;
    	//	and then create the frame
    	// The one and only window has been initialized, so show and update it.

    It is important that you create your console before you create the main window. If you don't, the console will still be created, but your debugging messages send with _cprintf() will not arrive in your console. I couldn't figure out why it is like this, only that it is like this. If somebody has an explanation, please let me know.

    Writing to the console

    Send your output to the console via _cprintf(), which is prototyped like this:
    int _cprintf( const char *format [, argument] ... );

    The format has the same form and function as the format parameter for the printf() function. Please look up the details in your documentation. And don't forget to #include <conio.h> wherever you use _cprintf().

    The CChildView::OnPaint() override in the demo application looks like this:

    void CChildView::OnPaint() 
    	CPaintDC dc(this); // device context for painting
    	// TODO: Add your message handler code here
    #ifdef _DEBUG
    	static int nCallCounter = 0;
    	_cprintf("Window painted now %i time(s)\n", nCallCounter);
    	// Do not call CWnd::OnPaint() for painting messages

    Getting rid of the console

    Somewhere near the end of your program you should call FreeConsole() to free the console <g>. Again, this function does not take any parameters and returns a BOOL indicating success or failure. Here is what the CWinApp::ExitInstance() override in the demo project looks like:

    int CSmplConsoleApp::ExitInstance() 
    	//	deallocate console
    #ifdef _DEBUG
    	if (!FreeConsole())
    		AfxMessageBox("Could not free the console!");
    	return CWinApp::ExitInstance();

    Hope that helps!


    This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

    A list of licenses authors might use can be found here


    About the Author

    matthias s.
    Web Developer
    Germany Germany
    I'm into photography a lot. And yes, I do code as well. Mostly C# these days.

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    Comments and Discussions

    GeneralMy vote of 3 Pin
    vontom4-Nov-11 3:26
    membervontom4-Nov-11 3:26 
    GeneralAwesome, thanks! Pin
    Johpoke9-Aug-11 7:30
    memberJohpoke9-Aug-11 7:30 
    QuestionHow to disable the Close Button of the Console Pin
    MosheDavid12314-Mar-10 5:51
    memberMosheDavid12314-Mar-10 5:51 
    GeneralMy vote of 2 Pin
    Panic2k310-Mar-10 20:33
    memberPanic2k310-Mar-10 20:33 
    Generalproblems with close button in the console Pin
    sankariyo22-Apr-08 0:30
    membersankariyo22-Apr-08 0:30 

    I have a dialog where pressing a button calls to AllocConsole()
    showing a console a pressing in another button on my dialog close the console calling FreeConsole(). Everything works fine.
    But if the console is closed using its close button then the next error appears:
    "user breakpoint called from code at 0x7c901230".

    So a possible solution should be disable the close button at the console.

    Is anybody knows what to do to avoid the error message when closing the console via close button (x). Or how to disable such a button.

    Thanks in advance.

    My best regards.
    GeneralJust another possiblity: redirect TRACE Pin
    Franz Renesnicek20-Sep-00 3:43
    sussFranz Renesnicek20-Sep-00 3:43 
    GeneralClosing console with X button Pin
    Louis Daoust2-Aug-00 10:39
    sussLouis Daoust2-Aug-00 10:39 
    GeneralRe: Closing console with X button Pin
    Matthias Steinbart2-Aug-00 20:51
    sussMatthias Steinbart2-Aug-00 20:51 
    GeneralRe: Closing console with X button Pin
    Paolo Messina13-Aug-00 11:07
    sussPaolo Messina13-Aug-00 11:07 
    GeneralRe: Closing console with X button Pin
    Louis Daoust16-Aug-00 6:00
    sussLouis Daoust16-Aug-00 6:00 
    GeneralRe: Closing console with X button Pin
    Paolo Messina18-Aug-00 10:05
    sussPaolo Messina18-Aug-00 10:05 
    GeneralRe: Closing console with X button Pin
    Louis Daoust18-Aug-00 10:41
    sussLouis Daoust18-Aug-00 10:41 
    GeneralRe: Closing console with X button Pin
    Paolo Messina19-Aug-00 7:26
    sussPaolo Messina19-Aug-00 7:26 
    QuestionWhat about DebugView Pin
    Paul E. Bible20-Jun-00 10:43
    sussPaul E. Bible20-Jun-00 10:43 
    AnswerRe: What about DebugView Pin
    Matthias Steinbart28-Jun-00 22:18
    sussMatthias Steinbart28-Jun-00 22:18 
    GeneralRe: What about DebugView Pin
    Djibril18-Dec-00 8:56
    memberDjibril18-Dec-00 8:56 
    GeneralRe: What about DebugView Pin
    Anonymous29-Mar-01 7:03
    memberAnonymous29-Mar-01 7:03 
    GeneralEven Easier Way Pin
    Michael A. Cornelius19-Jun-00 4:43
    sussMichael A. Cornelius19-Jun-00 4:43 
    GeneralNice one! Pin
    Matthias Steinbart28-Jun-00 22:21
    sussMatthias Steinbart28-Jun-00 22:21 
    GeneralVery nice ! Pin
    Hostalet26-Aug-02 0:26
    sussHostalet26-Aug-02 0:26 
    GeneralRe: Even Easier Way Pin
    skst8-Jul-03 11:41
    memberskst8-Jul-03 11:41 

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