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Ido Talbi's blog

Namespaces in C

After showing you how to add exceptions, I will now show you how to add namespaces to C *

* this is a bad idea.

The solution I will showcase involves a struct which holds function pointers to all the functions in the scope. Obviously, an immediate issue that arises is the fact that your “namespace” cannot hold types, only actual variables.

In summary, here is how to create your own namespace, in C, right now!:

  1. Create a (nameless) struct and give a variable of the type the name of your namespace
  2. Create the fptr macro (optional) and declare all the (pointer) functions in your namespace
  3. Initialize the variable’s pointers with the desired functions

fin.

Here’s how that looks:

/*brilliant macro, highly recommended*/

#define fptr(RETURN_VALUE, ptr_name, ...) RETURN_VALUE (*ptr_name)(__VA_ARGS__)

#include <stdio.h>
#include <stdlib.h> /*we must include these before initializing our namespace*/

struct {
    fptr(FILE*, fopen, const char *restrict, const char *restrict);
    fptr(int, fclose, FILE*);
    fptr(int, fprintf, FILE *restrict, const char *restrict, ...);
    fptr(int, printf, const char *restrict, ...);
    fptr(int, puts, const char*);
    fptr(void*, malloc, size_t);
    fptr(void, free, void*);
    const int esuccess;
    const int efailure;
    /*etc.*/
} std = {
    /*C99 designated initializer*/
    .fopen    = &fopen,
    .fclose   = &fclose,
    .fprintf  = &fprintf,
    .printf   = &printf,
    .puts     = &puts,
    .malloc   = &malloc,
    .free     = &free,
    .esuccess = EXIT_SUCCESS,
    .efailure = EXIT_FAILURE,
    /*...*/
};

and, using it is as simple as it can be (which is quite surprising!):

int main(void) {
    int x = 3;

    std.printf("%d\n", x);
    FILE* f = std.fopen("my_file.txt", "r");
  /*^^^^ you can't have types inside structs*/
    std.fprintf(f, "x = %d\n", x);
    std.fclose(f);
}

Conclusions

  • This is a very dumb idea, please don’t use it
  • If you really want namespaces, use C++
  • If you must use C, then I’d recommend just naming your functions accordingly, such as mylib_<some_function> (which is how you should already be naming your functions)
  • This is actually better then expected, and actually seems quite nice… don’t use this though
https://blog.tal.bi/posts/namespaces-in-c/ talbi