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Re: g_error_free() warning on null pointer

Recently I was re-educated by the Java people that using a null on free
is how they regularly force various Java handling routines they rely on SEGFAULT.

On 8/15/2015 4:54 PM, Michael McConville wrote:
Jasper St. Pierre wrote:
Lots of things in GLib fail when passed a NULL pointer, like
I'm talking about free()-family functions specifically, though. They
have a POSIX-specified behavior that people expect.

The idea is that passing a NULL pointer is probably a sign of a bug
somewhere, so you shouldn't do it.
I definitely don't think it's evidence of a bug. This is common practice
in POSIX-compliant C. More to follow.

While the C standard's free() is NULL-safe, I'd say that this is quite
strange for the C standard, since any other invalid pointer passed to
free() would (most likely, though yes, implementation-defined) crash.
Rather than strange, I'd say it was intentional and insightful. In
function bodies, you often have pointers that are used in conditions and
may or may not be null. There's a very easy and clean way to deal with
this: initialize them to NULL at the beginning and free them at the end.
Freeing conditionally in the body can be awkward and often leads to
memory leaks. I can send you a few examples from the Pidgin codebase if
you're interested.

More circumstantially, the entire POSIX description for free() is four
sentences. I doubt that allowing null pointers was added as a
complicating distraction. It's a core part of a simple interface.

I'm not insisting that you code this way. Most simply, I'd say:

  * many programmers already assume POSIX compliance
  * g_free() already complies with POSIX on this
  * people clearly associate g_error_free() et al. with free() and
  * these functions might as well behave the same

I really can't imagine anyone using these warnings. I can imagine people
being distracted or misled by them, though - I was.
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