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

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

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