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Posted 17 Jun 2000


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Creating a Console for Your MFC App's Debug Output

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17 Jun 2000
How to send debugging output to a console in a MFC application

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 first, I didn't have an IDE on the PC where I tested the debug-builds of my app and second, 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!


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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.

Comments and Discussions

SuggestionTip Pin
Michael Haephrati29-Nov-20 8:38
professionalMichael Haephrati29-Nov-20 8:38 
GeneralMy vote of 3 Pin
vontom4-Nov-11 2:26
Membervontom4-Nov-11 2:26 
GeneralAwesome, thanks! Pin
Johpoke9-Aug-11 6:30
MemberJohpoke9-Aug-11 6:30 
QuestionHow to disable the Close Button of the Console Pin
MosheDavid12314-Mar-10 4:51
MemberMosheDavid12314-Mar-10 4:51 
GeneralMy vote of 2 Pin
Panic2k310-Mar-10 19:33
MemberPanic2k310-Mar-10 19:33 
Generalproblems with close button in the console Pin
sankariyo21-Apr-08 23:30
Membersankariyo21-Apr-08 23:30 
GeneralJust another possiblity: redirect TRACE Pin
Franz Renesnicek20-Sep-00 2:43
MemberFranz Renesnicek20-Sep-00 2:43 
GeneralClosing console with X button Pin
ldaoust2-Aug-00 9:39
Memberldaoust2-Aug-00 9:39 
GeneralRe: Closing console with X button Pin
Matthias Steinbart2-Aug-00 19:51
sussMatthias Steinbart2-Aug-00 19:51 
GeneralRe: Closing console with X button Pin
Paolo Messina13-Aug-00 10:07
professionalPaolo Messina13-Aug-00 10:07 
GeneralRe: Closing console with X button Pin
ldaoust16-Aug-00 5:00
Memberldaoust16-Aug-00 5:00 
GeneralRe: Closing console with X button Pin
Paolo Messina18-Aug-00 9:05
professionalPaolo Messina18-Aug-00 9:05 
GeneralRe: Closing console with X button Pin
ldaoust18-Aug-00 9:41
Memberldaoust18-Aug-00 9:41 
GeneralRe: Closing console with X button Pin
Paolo Messina19-Aug-00 6:26
professionalPaolo Messina19-Aug-00 6:26 
QuestionWhat about DebugView Pin
Paul E. Bible20-Jun-00 9:43
MemberPaul E. Bible20-Jun-00 9:43 
AnswerRe: What about DebugView Pin
Matthias Steinbart28-Jun-00 21:18
sussMatthias Steinbart28-Jun-00 21:18 
GeneralRe: What about DebugView Pin
Djibril18-Dec-00 7:56
professionalDjibril18-Dec-00 7:56 
GeneralRe: What about DebugView Pin
29-Mar-01 6:03
suss29-Mar-01 6:03 
GeneralEven Easier Way Pin
Michael A. Cornelius19-Jun-00 3:43
sussMichael A. Cornelius19-Jun-00 3:43 
GeneralNice one! Pin
Matthias Steinbart28-Jun-00 21:21
sussMatthias Steinbart28-Jun-00 21:21 
GeneralVery nice ! Pin
Hostalet25-Aug-02 23:26
sussHostalet25-Aug-02 23:26 
GeneralRe: Even Easier Way Pin
skst8-Jul-03 10:41
Memberskst8-Jul-03 10:41 

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