анализировать аргументы подопции из строки (parse suboption arguments from a string)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
getsubopt — parse suboption arguments from a string
Синопсис (Synopsis)
#include <stdlib.h>
int getsubopt(char **optionp, char * const *keylistp, char **valuep);
Описание (Description)
The getsubopt() function shall parse suboption arguments in a
flag argument. Such options often result from the use of
getopt().
The getsubopt() argument optionp is a pointer to a pointer to the
option argument string. The suboption arguments shall be
separated by <comma> characters and each may consist of either a
single token, or a token-value pair separated by an <equals-
sign>.
The keylistp argument shall be a pointer to a vector of strings.
The end of the vector is identified by a null pointer. Each entry
in the vector is one of the possible tokens that might be found
in *optionp. Since <comma> characters delimit suboption arguments
in optionp, they should not appear in any of the strings pointed
to by keylistp. Similarly, because an <equals-sign> separates a
token from its value, the application should not include an
<equals-sign> in any of the strings pointed to by keylistp. The
getsubopt() function shall not modify the keylistp vector.
The valuep argument is the address of a value string pointer.
If a <comma> appears in optionp, it shall be interpreted as a
suboption separator. After <comma> characters have been
processed, if there are one or more <equals-sign> characters in a
suboption string, the first <equals-sign> in any suboption string
shall be interpreted as a separator between a token and a value.
Subsequent <equals-sign> characters in a suboption string shall
be interpreted as part of the value.
If the string at *optionp contains only one suboption argument
(equivalently, no <comma> characters), getsubopt() shall update
*optionp to point to the null character at the end of the string.
Otherwise, it shall isolate the suboption argument by replacing
the <comma> separator with a null character, and shall update
*optionp to point to the start of the next suboption argument. If
the suboption argument has an associated value (equivalently,
contains an <equals-sign>), getsubopt() shall update *valuep to
point to the value's first character. Otherwise, it shall set
*valuep to a null pointer. The calling application may use this
information to determine whether the presence or absence of a
value for the suboption is an error.
Additionally, when getsubopt() fails to match the suboption
argument with a token in the keylistp array, the calling
application should decide if this is an error, or if the
unrecognized option should be processed in another way.
Возвращаемое значение (Return value)
The getsubopt() function shall return the index of the matched
token string, or -1 if no token strings were matched.
Ошибки (Error)
No errors are defined.
The following sections are informative.
Примеры (Examples)
Parsing Suboptions
The following example uses the getsubopt() function to parse a
value argument in the optarg external variable returned by a call
to getopt().
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int do_all;
const char *type;
int read_size;
int write_size;
int read_only;
enum
{
RO_OPTION = 0,
RW_OPTION,
READ_SIZE_OPTION,
WRITE_SIZE_OPTION
};
const char *mount_opts[] =
{
[RO_OPTION] = "ro",
[RW_OPTION] = "rw",
[READ_SIZE_OPTION] = "rsize",
[WRITE_SIZE_OPTION] = "wsize",
NULL
};
int
main(int argc, char *argv[])
{
char *subopts, *value;
int opt;
while ((opt = getopt(argc, argv, "at:o:")) != -1)
switch(opt)
{
case 'a':
do_all = 1;
break;
case 't':
type = optarg;
break;
case 'o':
subopts = optarg;
while (*subopts != ' ')
{
char *saved = subopts;
switch(getsubopt(&subopts, (char **)mount_opts,
&value))
{
case RO_OPTION:
read_only = 1;
break;
case RW_OPTION:
read_only = 0;
break;
case READ_SIZE_OPTION:
if (value == NULL)
abort();
read_size = atoi(value);
break;
case WRITE_SIZE_OPTION:
if (value == NULL)
abort();
write_size = atoi(value);
break;
default:
/* Unknown suboption. */
printf("Unknown suboption `%s'\n", saved);
abort();
}
}
break;
default:
abort();
}
/* Do the real work. */
return 0;
}
If the above example is invoked with:
program -o ro,rsize=512
then after option parsing, the variable do_all will be 0, type
will be a null pointer, read_size will be 512, write_size will be
0, and read_only will be 1. If it is invoked with:
program -o oops
it will print:
"Unknown suboption `oops'"
before aborting.
Использование в приложениях (Application usage)
The value of *valuep when getsubopt() returns -1 is unspecified.
Historical implementations provide various incompatible
extensions to allow an application to access the suboption text
that was not found in the keylistp array.
Обоснование (Rationale)
The keylistp argument of getsubopt() is typed as char * const *
to match historical practice. However, the standard is clear that
implementations will not modify either the array or the strings
contained in the array, as if the argument had been typed const
char * const *.
Будущие направления (Future directions)
None.
Смотри также (See also)
getopt(3p)
The Base Definitions volume of POSIX.1‐2017, stdlib.h(0p)
