How to know file type

[calhal]

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