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

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

To print to the "real" console, you need to make it visible by using the linker flag /SUBSYSTEM:CONSOLE. The extra console window is annoying, but for debugging purposes it's very valuable.

OutputDebugString prints to the debugger output when running inside the debugger.

Answer 3

Your Win32 project is likely a GUI project, not a console project. This causes a difference in the executable header. As a result, your GUI project will be responsible for opening its own window. That may be a console window, though. Call AllocConsole() to create it, and use the Win32 console functions to write to it.