[cffi-devel] Re: CFFI malloc free

[Hoehle, Joerg-Cyril]

Hi,

>>  If I have a C function which allocates memory for a C string and returns a
>> pointer to this memory (return type char *).
>> How do I deallocate this memory? Should I use 
>>`foreign-string-free' or `foreign-free'. 
>I have been meaning to look into this. Right now, you'd have to use
>something like (foreign-funcall "free" :pointer <your-pointer>)

I don't understand why there's something unclear here.
I thought that's why :string+ptr had been invented.

This is exactly the pattern of :string+ptr, and it's embodied in
tests/misc-types.lisp:deftest misc-types.string+ptr:
  a) return string and
  b) (foreign-free pointer)
Is that testcase broken? "Just" non-portable?

Well, since foreign-free's specification is to free only things allocated with foreign-alloc, maybe CFFI must export the general C free() as well?
The :string+ptr type should then documented this.

Note that malloc()/free() is fine for a UNIX shared library. It's somewhat meaningless in the context of a DLL on MS-Windows. But there, one will probably not encounter such a protocol and will have to call the resource free'ing function via the FFI as well.

Regards,
	Jorg Hohle.