Re: working with bitmaps in C


"Flash Gordon" <spam@xxxxxxxxxxxxxxxxxx> wrote in message
Malcolm McLean wrote, On 27/12/07 17:16:
Actually, the best thing is normally to start off by checking the length is within a valid range, then check the data is valid, then check that you hit a valid tag in the place expected. If any of those things fail you report the file as being corrupt or a format you can't handle.

The object of the exercise is to read the data, not to check the file for adherence to the format.

That's a good point. It should be returning -1 instead of zero on an unrecognised header size, at least. Probably we should try to read it as a 40. However to do a really good job we've got to skip to the raster bits, which means a total rewrite and lots of complications.

Don't advertise your code as being reliable then, advertise it as supporting some but not all BMP files.

The question is what to do with as yet unspecified versions. Presumably MS will extend the header field, maybe add new chunks. The question is whether the raster data will still be readable without the new information, and it is impossible for MS to guarantee that, because they won't change the format for fun, but because some need arises.
I should be able to read every current format, barring bugs, but some are obsolete.

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