Some bits on malloc(0) in C being allowed to return NULL

Ages ago I worked with a system where malloc(0) incremented a counter and returned -1.

free(-1) decremented the counter.

This way you could check for leaks :p

I might be missing something, but how does this help in checking for leaks? I mean, I guess you could use it to check for leaks specifically of 0-sized allocations, but wouldn’t it be better just to return NULL and guarantee that 0-sized allocations never use any memory at all?

At the end of main, if the count wasn't balanced, then you knew you had a mismatch between malloc()/free().

If malloc() had returned a real pointer, you'd have to free that too.

> wouldn’t it be better just to return NULL and guarantee that 0-sized allocations never use any memory at all?

Better: takes less memory Worse: blinds you to this portability issue.

> At the end of main, if the count wasn't balanced, then you knew you had a mismatch between malloc()/free().

A mismatch between malloc(0) and free(-1).

You’d know nothing about calls to malloc with non-zero sizes.