I have a uni-code string in Arabic to display in output window rather than in console, so I could only use OutputDebugStringW, and I call SetConsoleOutputCP(1256) to set Arabic code page but still it only output "????". What should I do...
This is a documented restriction for OutputDebugStringW():
OutputDebugStringW converts the specified string based on the current system locale information and passes it to OutputDebugStringA to be displayed. As a result, some Unicode characters may not be displayed correctly.
Calling SetConsoleOutputCP() doesn't solve the problem, that changes the code page for the console window, not the debugger. You'd have to change your system locale, Control Panel + Region, Administrative tab. If Arabic is your favorite language then changing it to 1256 is the appropriate thing to do. It will of course have system-wide effects.