What type should I use for an index variable.

Question

This is a best practices question. I am making an array

type * x = malloc(size*sizeof(type));

AFAIK sizeof gives a return value of size_t. Does that mean that I should use a size_t to declare, or pass around size? Also when indexing the array should I also use a size_t for the index variable? What is the best practice for these these? This is not something that they taught in school, and now that I'm getting into serious c++ I want to know.

Also if anyone has references of where I can find best practices for this kind of stuff it would be helpful? Kind of an etiquette for programmers book.

EDIT: The malloc should be cudaHostAlloc, or cudaMalloc, since I am developing a class that stores an array simultaneously on the device and host, and updates both at the same time. So malloc here is just a place holder for what I'll actually be doing.

Answer 1

In reference to your follow-on question:

The best reference I have used for general high-level programming "current good practices" sort of thing is:

Code Complete by Steve McConnell (ISBN 0-7356-1967-0)

I reference it all the time. When my company formalized its coding standards, I wrote them based off of it. It doesn't go into design or architecture as much, but for actually banging out code, the book is appropriately named.

Answer 2

Well, since you've already abandoned best practice, even GOOD practice, by using malloc...why does it really matter?

That said, I generally use size_t unless I need a type that can go negative for various semi-rare conditions.

Answer 3

In general, I use whatever minimizes the number of implicit or explicit casts and warning errors. Generally there is a good reason why things are typed the way they are. size_t is a good choice for array index, since it's unsigned and you don't generally want to access myarray[-1], say.

btw since this is C++ you should get out of the habit of using malloc (free) which is part of CRT (C runtime library). Use new (delete), preferably with smart pointers to minimize manual memory handling.

Once you have mastered the basics, a good practices reference (language-specific) is Effective C++ by Scott Meyers. The logical next step is Effective STL.

Answer 4

If you are coding in C++, why are you using malloc anyways? That's just asking for trouble. If you are making an array, I'd be looking at Vector<> which bypasses the need for programmer managed memory completely. Seriously, anytime I find myself using a naked 'new' in code, I look closely to see why a smart pointer or container isn't in use instead. if done right, you never have to worry about delete, delete[], or even free again.

Answer 5

cudaMalloc takes a size of type size_t, so for consistency, that's what you should use for indices.

Answer 6

I would prefer int over size_t for a couple reasons:

1. primitive types should be preferred unless the typedef provides something fundamentally new, size_t here doesn't
2. the size_t is defined differently on different systems, possibly creating surprises for some developers
3. signed int avoids for (size_t i=9; i>=0; --i) bugs, as well as other bugs in conditionals, e.g. if (result < 1) or if ((i-2)/2 < 1)

size_t is a useless abstraction that masks undesired behavior by silencing underflows