The first argument to the
argp_parse function is a pointer to a
struct argp, which is known as an argp parser:
This structure specifies how to parse a given set of options and arguments, perhaps in conjunction with other argp parsers. It has the following fields:
const struct argp_option *options
A pointer to a vector of
argp_option structures specifying which
options this argp parser understands; it may be zero if there are no
options at all. See Specifying Options in an Argp Parser.
A pointer to a function that defines actions for this parser; it is
called for each option parsed, and at other well-defined points in the
parsing process. A value of zero is the same as a pointer to a function
that always returns
ARGP_ERR_UNKNOWN. See Argp Parser Functions.
const char *args_doc
If non-zero, a string describing what non-option arguments are called by this parser. This is only used to print the ‘Usage:’ message. If it contains newlines, the strings separated by them are considered alternative usage patterns and printed on separate lines. Lines after the first are prefixed by ‘ or: ’ instead of ‘Usage:’.
const char *doc
If non-zero, a string containing extra text to be printed before and
after the options in a long help message, with the two sections
separated by a vertical tab (
'\013') character. By
convention, the documentation before the options is just a short string
explaining what the program does. Documentation printed after the
options describe behavior in more detail.
const struct argp_child *children
A pointer to a vector of
argp_child structures. This pointer
specifies which additional argp parsers should be combined with this
one. See Combining Multiple Argp Parsers.
char *(*help_filter)(int key, const char *text, void *input)
If non-zero, a pointer to a function that filters the output of help messages. See Customizing Argp Help Output.
const char *argp_domain
If non-zero, the strings used in the argp library are translated using the domain described by this string. If zero, the current default domain is used.
Of the above group,
doc fields are usually all that are needed. If an argp
parser is defined as an initialized C variable, only the fields used
need be specified in the initializer. The rest will default to zero due
to the way C structure initialization works. This design is exploited in
most argp structures; the most-used fields are grouped near the
beginning, the unused fields left unspecified.