Re: Weird problems with C extension and bytea as input type

On Wed, Mar 23, 2011 at 5:08 AM, Adrian Schreyer <ams214@cam.ac.uk> wrote:
>
> you are right, it returns a char *.
>
> The prototype:
>
> char *function(bytea *b);
>
> The actual C++ function looks roughly like this
>
> extern "C"
> char *function(bytea *b)
> {
>   string ism;
>   [...]
>   return ism.c_str();
> }
>


Don't do that.  You are returning a pointer to an unallocated buffer
(previously held by a local variable).  c_str() is just a const
pointer to a buffer held inside "ism".  When ism goes out of scope,
that buffer if freed.

Either return "std::string", or strdup() the string and have the
caller free that.  (but use the postgresql alloc pool function to
handle the strdup.  I don't recall that function's name off the top of
my head).