Have you tried reading it as BigEndian (using the N template)? It kinda
looks like BigEndian to me, but I get easily turned around by endianness...
-Mike
Barry Brevik wrote:
> I am writing an app which, at a certain point, needs to read a .PNG
> graphics file.
>
> The .PNG file is always small, so I read the whole file (binmode) into a
> scalar, and this works well.
>
> if ($gfilesize = -s $gfilespec)
> {
> $GRAPHFILE = "<$gfilespec";
> if (open GRAPHFILE)
> {
> binmode GRAPHFILE;
> read GRAPHFILE, $gbuffer, $gfilesize;
> close GRAPHFILE;
>
> The size of the file ($gfilesize) matches the size of the scalar
> ($gbuffer). This is good.
>
> Then I proceed to paw through the buffer. The 1st 8 bytes of the file is
> a signature, which I read and deal with. Then, the file is a series of
> chunks where the 1st 4 bytes is a 32 bit number representing the size of
> the chunk, and the 2nd 4 bytes is an ASCII "chunk name", such as "IHDR".
>
> So, after the signature, the next 8 bytes look like this:
>
> 00 00 00 0d 49 48 44 52 . . . . I H D R
>
> I am trying to decode this with the following:
>
> $bufptr = 8;
> ($chunksize, $chunkname) = unpack "L a4", substr($gbuffer, $bufptr,
> 8);
>
> Actually, I've tried every permutation of "unpack" template that I can
> think of.
>
> The problem is that the 2nd scalar ($chunkname) comes out fine as
> "IHDR", but the first scalar comes out as "218103808" which is wrong as
> you can see above, it should be "13".
>
> I thought I was starting to understand unpack, but what am I doing
> wrong??
>
> Barry Brevik
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