OutputDebugString
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OutputDebugString( ) is a Windows method for emitting a text string to some output device (window/file/external debugger).
Lazarus will show these messages in the IDE Window: Event Log accessible from Main menu > View > Debug Windows > Event Log. Alternatively, the shortcut keys Ctrl+Alt+V will open the Event Log window.
Note: You will need to include the Windows unit for the WinAPI in your application's Uses clause.