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Gui toolkits, which should I use?
What is the best library to use when writing GUI applications in C++?
I wanted to create a program compatible on both Windows and Mac OS X using C++ but I am uncertain of what to use for forms, windows, etc. Would I have to convert the code later on, is there some alternative GUI I can use, or could I even create custom forms using basic C++ code?
Be very strict about the MVC separation. Implement the view twice: once for Windows API with C++, once for Cocoa with Obj-C. Link as appropriate.
If you don’t care about the native look and feel, use Qt as Saif suggested.