Why doesn't ANSI C have namespaces?

Question

Having namespaces seems like no-brainer for most languages. But as far as I can tell, ANSI C doesn\'t support it. Why not? Any plans to include it in a future standard?

Answer 1

C doesn't support namespaces like C++. The implementation of C++ namespaces mangle the names. The approach outlined below allows you to get the benefit of namespaces in C++ while having names that are not mangled. I realize that the nature of the question is why doesn't C support namespaces (and a trivial answer would be that it doesn't because it wasn't implemented :)). I just thought that it might help someone to see how I've implemented the functionality of templates and namespaces.

I wrote up a tutorial on how to get the advantage of namespaces and/or templates using C.

Namespaces and templates in C

Namespaces and templates in C (using Linked Lists)

For the basic namespace, one can simply prefix the namespace name as a convention.

namespace MY_OBJECT {
  struct HANDLE;
  HANDLE *init();
  void destroy(HANDLE * & h);

  void do_something(HANDLE *h, ... );
}

can be written as

struct MY_OBJECT_HANDLE;
struct MY_OBJECT_HANDLE *my_object_init();
void my_object_destroy( MY_OBJECT_HANDLE * & h );

void my_object_do_something(MY_OBJECT_HANDLE *h, ... );

A second approach that I have needed that uses the concept of namespacing and templates is to use the macro concatenation and include. For example, I can create a

template T multiply( T x, T y ) { return x*y }

using template files as follows

multiply-template.h

_multiply_type_ _multiply_(multiply)( _multiply_type_ x, _multiply_type_ y);

multiply-template.c

_multiply_type_ _multiply_(multiply)( _multiply_type_ x, _multiply_type_ y) {
  return x*y;
}

We can now define int_multiply as follows. In this example, I'll create a int_multiply.h/.c file.

int_multiply.h

#ifndef _INT_MULTIPLY_H
#define _INT_MULTIPLY_H

#ifdef _multiply_
#undef _multiply_
#endif
#define _multiply_(NAME) int ## _ ## NAME 

#ifdef _multiply_type_
#undef _multiply_type_
#endif
#define _multiply_type_ int 

#include "multiply-template.h" 
#endif

int_multiply.c

#include "int_multiply.h"
#include "multiply-template.c"

At the end of all of this, you will have a function and header file for.

int int_multiply( int x, int y ) { return x * y }

I created a much more detailed tutorial on the links provided which show how it works with linked lists. Hopefully this helps someone!