Le 16 janv. 07 à 02:13 Matin, Dennis Birch a écrit:
On 1/15/07, Dennis Birch <[EMAIL PROTECTED]> wrote:
On 1/15/07, Arnaud Nicolet <[EMAIL PROTECTED]> wrote:
> Le 16 janv. 07 à 01:48 Matin, Dennis Birch a écrit:
>
> > On 1/15/07, Louis G5 Batayte <[EMAIL PROTECTED]> wrote:
> >>
> >> MacOS X 10.4.8 RB 2007R1
> >>
> >> I let the user select a folder, then I search through the
items in
> >> that folder looking for jpeg files. Right now I am looking at
the
> >> extension to determine if it is a jpeg or not. But I am
trying to
> >> determine if a file without an extension is a jpeg file. If
I take a
> >> jpeg file with an extension, and use the MacOS System "Get
Info" to
> >> delete the extension, the System "Get Info" still displays
the "Kind"
>
> >> as a jpeg file. But I cannot figure how to determine this from
> >> within RealBasic. When I look at the contents of the
folderitem, for
> >> the file without the jpeg extension, in debug mode, there is
> >> nothing there to indicate the file type/kind. Any suggestions?
> >
> >
> >> From looking at a handful of JPEG files in a hex editor, it
> >> appears that the
> > first 10 bytes of every JPEG file is identical: ff d8 ff e0 00 10
> > 4a 46 49
> > 46. So you might consider opening each file, or each
questionable file
> > perhaps, and reading the first 10 bytes of its binarystream to
see
> > if it
> > matches that pattern.
>
> What about if I create an application which writes files with the
> same pattern?
> I mean: is reading bytes of a file a reliable way to determine it's
> contents?
I suspect that those 10 bytes (and possibly more) are a standard file
header for JPEG files. I also suspect it should be possible to
confirm or
disprove that pretty easily with a simple Web search. If that is a
standard
file header, then it seems to me it would be a safe method of
determining a
file's type. On the other hand, you raise a good point in that
there's
nothing to prevent somebody from writing a non-JPEG file with
those 10 bytes
at the beginning.
I just did a search for "jpeg file header" and here's a nice
reference I
found:
<http://www.obrador.com/essentialjpeg/headerinfo.htm>
thanks
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