I\'m examining the feasibility of porting an existing Windows MFC control to OS X/Carbon. My test bed is a C++ Carbon application generated using the XCode 3 Wizard.
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In Xcode you can see the output of std::cout/std::cerr in the "console" window (Run->Console).
std::cout
std::cerr
There is also Console.app (in /Applications/Utilities) which logs all output written to std::cerr from GUI applications.