Logging on Windows – OutputDebugString

Shows OutputDebugString being calld in the debuggerIn the post about rsyslog three days ago, I explained how to log from Linux programs using the rsyslog daemon.

It’s slightly different in Windows. There’s a built in function called OutputDebugString(LPCWSTR str) that you can call from anywhere in your program. It dumps the string¬†str into the Output window if you are debugging it in Visual Studio.

If you are running this outside of a debugger, the output is lost unless you can capture it with a suitable utility. DebugView from SysInternals.com (it redirects to Microsoft) is one such utility. That’s a screenshot of it below.

Showing DebugView in actionJust run DebugView and leave it there. It might catch other stuff from Windows, but when you run your program from the command line or double click on it, it will execute quickly and you’ll see any strings captured like this one.


This is the program that I ran. In Release it compiles to a 9 KB exe! Because OutPutDebugString needs a LPCWSTR  (Long Pointer to a WideString), I declared the text as wchar_t.

#include <Windows.h>

int main()
    wchar_t * text=L"Hello World!\n";

At work I developed a very large program that only worked running on another computer. I used OutputDebugString extensively and without it, debugging would have been much harder.