Le 16 janv. 07 à 02:07 Matin, Dennis Birch a écrit:
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 think headers of most common file formats should be reserved. I
doubt it's possible, but, in my opinion, it would be safe.
On the other hand, one may simply read the 10 first bytes and open
the file as picture. If both are OK, it's a JPEG file._______________________________________________
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