The getopt function is defined in the unistd.h header file. This header
file is only available on posix compatible systems. For example, on
Windows it's not available when building without mingw.
Comparing signed and unsigned integer expressions can have unexpected
results because the signed integer will get promoted to an unsigned
integer. To avoid the warning, add an explicit cast to the unsigned
type, along with a check to catch negative values.
For applications supporting offline parsing (like libdivecomputer's own
dctool application), some device specific knowledge is still required in
order to map a particular model to the corresponding backend. The new
convenience function will take care of that internally.
The already existing dc_parser_new() function does the same, but
requires an open device handle, which makes it unsuitable for offline
parsing.
Libdivecomputer always uses metric units internally. But when reverse
engineering a device that stores everything using imperial units, it's
very convenient to be able to switch the output to imperial units too.
