Re: errmsg() clobbers errno

John Gorman <johngorman2(at)gmail(dot)com> writes:
> While debugging an extension I discovered that the errmsg()
> function zeros out errno.

So might a lot of other functions used in an ereport's arguments.

> This is annoying because if the process of assembling a meaningful
> error message happens to call errmsg() before calling strerror()
> we lose the strerror information.

This is why you should use %m and not strerror(errno). The infrastructure
for %m is set up so that errno is captured before evaluating any of the
ereport's arguments.

> I am attaching a patch to preserve errno across errmsg() calls.

This is pretty useless, unfortunately, because there are just too
many ways to bite yourself on the rear if you reference errno inside
the arguments of an ereport (or any other complicated nest of function
calls).

regards, tom lane