Re: How to know file type
Do not expect Qt to know every possible file type.
If it's some kind of bitmap you can use QImage or QPixmap to load the file without specifying the format - in that case the loader will try to guess the format by reading the file header and return appropriate value if there's a problem to determine it.
Edit:
Forgot to mention that after opening the file you can use for example
QImage::format().
Edit2:
Actually maybe QImageReader::format() would be better ;)
Re: How to know file type
Linux attempts to know as many file types as possible, you can use the Linux MIME system to detect the type. On Windows you are stuck with the file extension unless you open the files yourself and detect from a signature.