MSDN:Sends the specified string to the debugger of the current application. In the debug version of MFC, this macro sends the specified string to the debugger of the current application. In a release build, this macro compiles to nothing (no code is generated at all).
In the debug version of MFC, this macro sends the specified string to the debugger of the current application. In a release build, this macro compiles to nothing (no code is generated at all).