[PigWithASoul]

I'm a bit confused here.

I will be writing code on several different platforms, including Windows 7 64-bit, Ubuntu 64-bit, Mac OSX Snow Leopard 32/64-bit, etc.

I know that in C++, and depending on which compiler, integrated development environment, etc., the compilation process will compile the code to the target architecture for the processor using the operating system's API/GUI to execute the program, whether in a text-based interface(console window), or GUI window(mostly used).

But that's not the confusing part ... the confusing part is the bits.

Let's say I write a program in 32-bit Windows XP professional, release a compiled executable(.exe)extension, copy the file, and test it on my Windows 7 64-bit ... Windows 7 has a 32-bit sub-system ... will it work? Or what about on 32-bit Windows 7? Given the fact that I don't really understand the concept here on how many bits it is released in(depends on the OS I am assuming), does a 32/64 bit difference make any real significant difference or error occur between different versions of Windows, whether or not the bits are the same width(e.g. Windows 98 is 32-bit), or would it depend solely on the operating system?

PS: SDL uses 32-bit code, yet it can be compiled under x64 architecture with 64-bit Windows, and 64-bit IDEs as well. Is it just dependent on the final compilation steps always?

And I am not too sure on how porting works either ... how can you just port a native Windows program to Mac, while keeping it identical? What would the process be here? A complete change of code makeover, or just some tweeks and adjustments?

I'm not a total newbie on software development and hardware, but can any one clear this out for me so I can have a better perspective on this in future endeavors/moments?

Thanks.

[SpectresShadow]

For the bits, I would imagine that a 32 bit will work on both 32 and 64, but a 64 bit would only work on a 64 bit machine. I haven't paid much attention to that as most machines I work with nowadays are all 64 bit machines. As for the porting, unless your using Real studio, which compiles into all three major OS's, it will only work in it's native OS unless you actually tell it how to work in other OS's. That's what I know about it so if someone else who has more experience than me can say for sure on either one, please correct me if I'm wrong.