mu_parse_opts and mu_parse_subopts can fail for several
reasons. On failure, these functions will return an error code depending
on the reason for failure. The error code can be one of the following:
An option parsing error. This indicates that the user made an error when
specifying options on the command line. You may wish to print a help
message when mu_parse_opts returns this value (see Formatting Help for an example).
This indicates that an input/output error occurred while parsing the
arguments. This could indicate, for example, failure to open a file
specified as an argument to an option which has a arg_type field
of MU_OPT_FILE (see Option Structure).
This value is returned from mu_parse_opts when a callback returns
a nonzero value (see Option Callbacks). You can have your callback
set an error flag if you want more details.
int MU_OPT_ERR (int retval) ¶This macro returns true if retval is one of the above error codes.