How do I print to the debug output window in a Win

Question

I've got a win32 project that I've loaded into Visual Studio 2005. I'd like to be able to print things to the Visual Studio output window, but I can't for the life of me work out how. I've tried 'printf' and 'cout <<' but my messages stay stubbornly unprinted.

Is there some sort of special way to print to the Visual Studio output window?

Answer 1

You can use OutputDebugString. OutputDebugString is a macro that depending on your build options either maps to OutputDebugStringA(char const*) or OutputDebugStringW(wchar_t const*). In the later case you will have to supply a wide character string to the function. To create a wide character literal you can use the L prefix:

OutputDebugStringW(L"My output string.");

Normally you will use the macro version together with the _T macro like this:

OutputDebugString(_T("My output string."));

If you project is configured to build for UNICODE it will expand into:

OutputDebugStringW(L"My output string.");

If you are not building for UNICODE it will expand into:

OutputDebugStringA("My output string.");

Answer 2

If the project is a GUI project, no console will appear. In order to change the project into a console one you need to go to the project properties panel and set:

• In "linker->System->SubSystem" the value "Console (/SUBSYSTEM:CONSOLE)"
• In "C/C++->Preprocessor->Preprocessor Definitions" add the "_CONSOLE" define

This solution works only if you had the classic "int main()" entry point.

But if you are like in my case (an openGL project), you don't need to edit the properties, as this works better:

AllocConsole();
freopen("CONIN$", "r",stdin);
freopen("CONOUT$", "w",stdout);
freopen("CONOUT$", "w",stderr);

printf and cout will work as usual.

If you call AllocConsole before the creation of a window, the console will appear behind the window, if you call it after, it will appear ahead.

Answer 3

Consider using the VC++ runtime Macros for Reporting _RPTN() and _RPTFN()

You can use the _RPTn, and _RPTFn macros, defined in CRTDBG.H, to replace the use of printf statements for debugging. These macros automatically disappear in your release build when _DEBUG is not defined, so there is no need to enclose them in #ifdefs.

Example...

if (someVar > MAX_SOMEVAR) {
    _RPTF2(_CRT_WARN, "In NameOfThisFunc( )," 
         " someVar= %d, otherVar= %d\n", someVar, otherVar );
}

Or you can use the VC++ runtime functions _CrtDbgReport, _CrtDbgReportW directly.

_CrtDbgReport and _CrtDbgReportW can send the debug report to three different destinations: a debug report file, a debug monitor (the Visual Studio debugger), or a debug message window.

_CrtDbgReport and _CrtDbgReportW create the user message for the debug report by substituting the argument[n] arguments into the format string, using the same rules defined by the printf or wprintf functions. These functions then generate the debug report and determine the destination or destinations, based on the current report modes and file defined for reportType. When the report is sent to a debug message window, the filename, lineNumber, and moduleName are included in the information displayed in the window.