Node:Argp Parsers,
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Specifying Argp Parsers
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 Argp Option Vectors.
argp_parser_t 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 (
'\v' , '\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_children structures. This pointer
specifies which additional argp parsers should be combined with this
one. See Argp Children.
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 Argp Help Filtering.
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.
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Of the above group, options
, parser
, args_doc
, and
the 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.