How to use typeof in clang compiler without warning?

I want to use typeof in clang but not __typeof__. If I use typeof without declaring it I get warning the following warning

vector.c:14:5: warning: extension used [-Wlanguage-extension-token]
    vec_init(&a,5);
    ^
./vector.h:27:26: note: expanded from macro 'vec_init'
    ((vec_ptr)->data) = (typeof((vec_ptr)->data)) malloc((capacity) * (sizeof((*((vec_ptr)->data)))))      \
                         ^
1 warning generated.

then I thought defining it might solve it so I added the following code:

#ifndef typeof
#ifdef __clang__
#define typeof(x) __typeof__(x)
#endif
#endif

With the added pre-processor definition I get the following error:

In file included from vector.c:1:
./vector.h:5:9: warning: keyword is hidden by macro definition [-Wkeyword-macro]
#define typeof(x) __typeof__(x)
        ^
1 warning generated.

but I get no error if I use __typeof__ instead. How to solve this warning issue on clang?

Solution

At the point of posting this answer, typeof is not a standard feature but an experimental language extension. As such, if you insist on using it, do so with the awareness that you aren't writing standard C - and get warned accordingly from strict compilers.

However, typeof used to be a GNU extension but it will be included in C23. Although compiler support for adding this to strict standard C is still shaky (neither clang 15 nor gcc 12.2 will allow it when compiling as -std=c2x).

Either way, typeof is not a preprocessor #define but a keyword, so you can't use it with #ifndef.

For now, you can compile in clang or gcc with -std=gnu2x, until compiler support for C23 settles. But you still can't compile with -pedantic or you'll get a warning for using extensions.