free() syntax with arguments in C

Question

I am working on converting many C programs from Unix to Linux and this free() syntax caught my attention:

free((char *) area );

What's the difference between this and free( area ); ?

Answer 1

The signature of free is:

void free(void *ptr);

So if area is a pointer type that is returned by malloc or its cousins, the conversion in free((char *) area ); is pointless.

Unless... if the code is really, really old, that is, before ANSI C introduced void * as generic pointer. In that ancient time, char * is used as generic pointer.

Answer 2

If someone were storing a pointer to dynamic allocated data in a non-pointer type sanctioned by the standard, i.e. area is declared as intptr_t for example, this casts the non-pointer to a pointer type and allows it to be freed.

If area is already a pointer type, this makes no sense at all with any C code written in the last quarter-century.