Re: Question about the *= (and similar) operator

CBFalconer wrote:
Keith Thompson wrote:
"James Dow Allen" <jdallen2000@xxxxxxxxx> writes:

... snip ...
Yes, but I still think a discussion of gcc's peculiar optimization
re malloc() would be *more* interesting.
You made three points in your original article (subject "gcc knows
about malloc()"):

1. gcc assumes that malloc()'s return value is not an alias for
another pointer.

Compilers are allowed to use knowledge of functions in the standard
library. It's a reasonably cool optimization, but there's not all
that much more to say about it.

Of course it can make that assumption. malloc, if successful,
always return a pointer to fresh storage. realloc may not, but any
copies of the original pointer have to be deemed invalid after
calling realloc.

Our realloc can be a misbehaving child and needs attention. Consider..

int *ptr;
ptr = malloc(100 * sizeof *prt);
ptr = realloc(ptr, 200 * sizeof *ptr);

Assume malloc works and then realloc fails. We'll have ptr set to NULL and no reference to the memory malloc gave us. A leak!

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---
.

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