Question

I started to look into glibc (GNU Libc)
to understand how it’s written. In malloc.c, I found a piece of code as follow:

#ifndef void
#define void        void
#endif

Can someone please explain to me what this means? Isn’t void always defined?

Thanks

Answer 1

Looking at the git history, it was like this:

/*
  Void_t* is the pointer type that malloc should say it returns
*/

#ifndef Void_t
#if (__STD_C || defined(WIN32))
#define Void_t      void
#else
#define Void_t      char
#endif
#endif /*Void_t*/

This was a workaround for historical [C], which did not have void and malloc() returned char * instead of void. The code was removed by Ulrich Drepper in 2011. The commit does not seems to be generated by a script or anything automatic, so he must had his intension to define like that.

The commit message does not say anything about void:

Simplify malloc code

Remove all kinds of unused configuration options and dead code.