Why doesn't ANSI C have namespaces?

For completeness there are several ways to achieve the "benefits" you might get from namespaces, in C.

One of my favorite methods is using a structure to house a bunch of method pointers which are the interface to your library/etc..

You then use an extern instance of this structure which you initialize inside your library pointing to all your functions. This allows you to keep your names simple in your library without stepping on the clients namespace (other than the extern variable at global scope, 1 variable vs possibly hundreds of methods..)

There is some additional maintenance involved but I feel that it is minimal.

Here is an example:

/* interface.h */

struct library {
    const int some_value;
    void (*method1)(void);
    void (*method2)(int);
    /* ... */
};

extern const struct library Library;
/* interface.h */

/* interface.c */
#include "interface.h"

void method1(void)
{
   ...
}
void method2(int arg)
{
   ...
}

const struct library Library = {
    .method1 = method1,
    .method2 = method2,
    .some_value = 36
};
/* end interface.c */

/* client code */
#include "interface.h"

int main(void)
{
    Library.method1();
    Library.method2(5);
    printf("%d\n", Library.some_value);
    return 0;
}
/* end */

The use of . syntax creates a strong association over the classic Library_function() Library_some_value method. There are some limitations however, for one you can't use macros as functions.

C does have namespaces. One for structure tags, and one for other types. Consider the following definition:

struct foo
{
    int a;
};

typedef struct bar
{
    int a;
} foo;

The first one has tag foo, and the later is made into type foo with a typedef. Still no name-clashing happens. This is because structure tags and types (built-in types and typedef'ed types) live in separate namespaces.

What C doesn't allow is to create new namespace by will. C was standardized before this was deemed important in a language, and adding namespaces would also threaten backwards-compatibility, because it requires name mangling to work right. I think this can be attributed due to technicalities, not philosophy.

EDIT: JeremyP fortunately corrected me and mentioned the namespaces I missed. There are namespaces for labels and for struct/union members as well.

C has namespaces. The syntax is namespace_name. You can even nest them as in general_specific_name. And if you want to be able to access names without writing out the namespace name every time, include the relevant preprocessor macros in a header file, e.g.

#define myfunction mylib_myfunction

This is a lot cleaner than name mangling and the other atrocities certain languages commit to deliver namespaces.