I have a few years of experience writing Unix command line tools (no GUI experience) in python, C and C++, and only recently crossed into the GUI world (Cocoa and IOS only). I've learned quite a bit of objective-C and am getting to understand how cocoa MVC works. However, one of the apps I am developing needs a Windows version and I was wondering what a good place to start would be given that I have absolutely no Windows development experience.
I was thinking about using Visual C++ 2010 Express as my development platform (because it's free and because I don't need to learn C++). My application is relatively simple, it will have only two windows and spend most of the time running in the background. It will however need to communicate with the OS (load dll's etc) and an online server (HTTP methods) and I'm not sure whether Visual C++ Express edition gives me access to the required API's. Would a Windows Forms application suffice? Am I going about this the wrong way? Do I need to learn C#? Any advice will be appreciated.
If you are already happy with proper c++, visual Studio C++ express should suit you fine. Given that you are not making a complicated GUI, you don't even need to dip into the managed code - C++ express allows you to create proper c++ console and GUI apps. You also don't need to install the platform SDK - it is part of VS C++ express.
Not being managed C++, you will be able to share source files between your various projects. managed c++, despite the c++ in the name, really is a different enough language that it will be annoying to work with if you simultaneously have to deal with iso C++.
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Note: The native windows API is a C api, not a C++ framework. So it does not provide a rich set of classes in a coherent framework to deal with. On the other hand, while, large, it is actually quite simple to work with.
Also: Given that you are already familiar with Mac development, there is a LGPL (iirc) package called CFLite that builds on windows and that implements the C api that underlays the Objective-C Cocoa API.
If you use its abstratcions you can share a greater part of code between windows and Mac (and other platforms).
Other C++ IDE's you might want to consider:
both of which can be configured to use the MINGW port of GCC to windows.