libpng equivalent of errno?

Hi.

In general, programming under POSIX, I can get information
about
errors by reading errno:

if (read(fd, buf, len) == -1)
  switch (errno) {
    case EIO: handle_io_error(); break;
    case EAGAIN:
    case EWOULDBLOCK:
      printf("waiting...n");
      break;
    default:
      break;
  }

With libpng, of course I can set my own error handlers, but
how can I get more information about exactly what error
occurred? Currently, I'm checking errno inside my custom
IO functions, but what about, for example, when a file
turns out not to be a PNG file? Of course I could check
that
the error string is 'Not a PNG file' inside an error
handler,
but this seems messy. I'd much rather do something like:

   if (png->errno == LIBPNG_ERROR_NOTPNG)
     handle_invalid_png();

Is this possible, currently?

thanks,
MC

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At 05:26 AM 2/18/2007 +0000, mal content wrote:
>Of course I could check that
>the error string is 'Not a PNG file' inside an error
handler,
>but this seems messy.

That's all there is right now.  We did lay some of the
groundwork
for error-number handling a few years ago but there is still
a
little work to be done, namely embedding an error-number
string
in each error or warning message.  It's on my to-do list for
libpng-1.4.0

Glenn

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On 18/02/07, Glenn Randers-Pehrson <glennrpcomcast.net> wrote:
> At 05:26 AM 2/18/2007 +0000, mal content wrote:
> >Of course I could check that
> >the error string is 'Not a PNG file' inside an
error handler,
> >but this seems messy.
>
> That's all there is right now.  We did lay some of the
groundwork
> for error-number handling a few years ago but there is
still a
> little work to be done, namely embedding an
error-number string
> in each error or warning message.  It's on my to-do
list for libpng-1.4.0
>

I look forward to it.

thanks,
MC

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