CODEWITHSUNDEEP
cnamespaces
Overv
Overv

Reputation: 8529

Namespacing in C with structs

It is possible to imitate namespaces in C like this:

#include <stdio.h>
#include <math.h>

struct math_namespace {
    double (*sin)(double);
};
const struct math_namespace math = {sin};

int main() {    
    printf("%f\n", math.sin(3));

    return 0;
}

Are there any disadvantages to this, or just situations where a prefix makes more sense? It just seems cleaner to do it this way.

Upvotes: 5

Views: 391

Answers (4)

slkpg
slkpg

Reputation: 23

I have used this style for a while now. It helps organize the program without all of the excess baggage of an OOP language. There is no performance penalty because accessing a function pointer in C is the same as directly accessing the function. I like it enough that I even wrote a very short paper about it. It can be found on http://slkpg.1eko.com under the link "C with Structs" at the bottom of the page. The direct link is http://slkpg.1eko.com/cstructs.html.

Upvotes: 1

DigitalRoss
DigitalRoss

Reputation: 146073

Well, this does allow you to export your namespace and it does allow a client module to use a static or local version of something that's named sin. So, in that sense, it does actually work.

The downside is that it's not terribly ELF-friendly. The struct initialization is buried in the middle of a writable data page, and it needs to be patched up. Unless you are statically linking, this is a load-time fix-up. On the bright side, it just duplicates what the ELF dispatch table would have done, so I bet it isn't even any slower. On Windows I think the considerations are similar.

Upvotes: 0

md5
md5

Reputation: 23699

This method is already used in real projects such as the C Containers Library by Jacob Navia. C is not designed for object-oriented programming. This is not really efficient, since you have to (1) access to the structure and (2) dereference the function pointer. If you really want prefixes, I think changing your identifiers remains the best solution.

Upvotes: 3

QuentinUK
QuentinUK

Reputation: 3077

Why reinvent the wheel? One disadvantage is all the setting up which could go out of sync, and also to add to the namespace you have to change the structure.

And there's no 'using namespace' so you always have to specify it. What about and functions with different parameter types?

Upvotes: 0

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