Write debug output to console window

Thursday Feb 11th 1999 by Wang Weijun

Write debug output to console window

Environment: any MSVC

It's very common that we have to test our program on another machine where the Visual C++ IDE is not installed. So there will be no debug window for output. Logging into a file or keep popping up MessageBoxs are not very practical ways. An easy solution is to show the output strings in a console window.

Put the following code at the beginning of your app file or in a separate file.

#ifdef _DEBUG
    FILE* __fStdOut = NULL;
    HANDLE __hStdOut = NULL;

// width and height is the size of console window, if you specify fname, 
// the output will also be writton to this file. The file pointer is automatically closed 
// when you close the app
void startConsoleWin(int width=80, int height=25, char* fname = NULL);

void startConsoleWin(int width, int height, char* fname)
#ifdef _DEBUG
	SetConsoleTitle("Debug Window");
	__hStdOut = GetStdHandle(STD_OUTPUT_HANDLE);

	COORD co = {width,height};
	SetConsoleScreenBufferSize(__hStdOut, co);

		__fStdOut = fopen(fname, "w");

// Use wprintf like TRACE0, TRACE1, ... (The arguments are the same as printf)
int wprintf(char *fmt, ...)
#ifdef _DEBUG
	char s[300];
	va_list argptr;
	int cnt;

	va_start(argptr, fmt);
	cnt = vsprintf(s, fmt, argptr);

	DWORD cCharsWritten;

		WriteConsole(__hStdOut, s, strlen(s), &cCharsWritten, NULL);

		fprintf(__fStdOut, s);

	return 0;

In CWinApp::InitInstance() call startConsoleWin() and a console window will popup. Then use wprintf at places where you used to use TRACE. The output strings will then appear in the console window.

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