Question

I’ve been told that I should use size_t always when I want 32bit unsigned int, I don’t quite understand why, but I think it has something to do with that if someone compiles the program on 16 or 64 bit machines, the unsigned int would become 16 or 64 bit but size_t won’t, but why doesn’t it? and how can I force the bit sizes to exactly what I want?

So, where is the list of which datatype to use and when? for example, is there a size_t alternative to unsigned short? or for 32bit int? etc. How can I be sure my datatypes have as many bits as I chose at the first place and not need to worry about different bit sizes on other machines?

Mostly I care more about the memory used rather than the marginal speed boost I get from doubling the memory usage, since I have not much RAM. So I want to stop worrying will everything break apart if my program is compiled on a machine that’s not 32bit. For now I’ve used size_t always when i want it to be 32bit, but for short I don’t know what to do. Someone help me to clear my head.

On the other hand: If I need 64 bit size variable, can I use it on a 32bit machine successfully? and what is that datatype name (if i want it to be 64bit always) ?

Answer 1

size_t is not always 32-bit. E.g. It’s 64-bit on 64-bit platforms.

For fixed-size integers, stdint.h is best. But it doesn’t come with VS2008 or earlier – you have to download it separately. (It comes as a standard part of VS2010 and most other compilers).

Since you’re using VS2008, you can use the MS-specific __int32, unsigned __int32 etc types. Documentation here.

To answer the 64-bit question: Most modern compilers have a 64-bit type, even on 32-bit systems. The compiler will do some magic to make it work. For Microsoft compilers, you can just use the __int64 or unsigned __int64 types.