debug output from an ActiveX control

I'm developing an ActiveX control and I'd like to thro开发者_如何学Cw some debug output to the console area in tstcon32 like other controls are doing. What system call is doing that?

stdout doesn't seem to be it

Are you thinking of ATLTRACE2 ? "Reports warnings to an output device, such as the debugger window, according to the indicated flags and levels."

Most likely it's using OutputDebugString: http://msdn.microsoft.com/en-us/library/aa363362%28VS.85%29.aspx