Here are the details about how to call the
getopt function. To
use this facility, your program must include the header file
If the value of this variable is nonzero, then
getopt prints an
error message to the standard error stream if it encounters an unknown
option character or an option with a missing required argument. This is
the default behavior. If you set this variable to zero,
does not print any messages, but it still returns the character
to indicate an error.
getopt encounters an unknown option character or an option
with a missing required argument, it stores that option character in
this variable. You can use this for providing your own diagnostic
This variable is set by
getopt to the index of the next element
of the argv array to be processed. Once
getopt has found
all of the option arguments, you can use this variable to determine
where the remaining non-option arguments begin. The initial value of
this variable is
This variable is set by
getopt to point at the value of the
option argument, for those options that accept arguments.
Preliminary: | MT-Unsafe race:getopt env | AS-Unsafe heap i18n lock corrupt | AC-Unsafe mem lock corrupt | See POSIX Safety Concepts.
getopt function gets the next option argument from the
argument list specified by the argv and argc arguments.
Normally these values come directly from the arguments received by
The options argument is a string that specifies the option characters that are valid for this program. An option character in this string can be followed by a colon (‘:’) to indicate that it takes a required argument. If an option character is followed by two colons (‘::’), its argument is optional; this is a GNU extension.
getopt has three ways to deal with options that follow
non-options argv elements. The special argument ‘--’ forces
in all cases the end of option scanning.
POSIXLY_CORRECTor beginning the options argument string with a plus sign (‘+’).
getopt function returns the option character for the next
command line option. When no more option arguments are available, it
-1. There may still be more non-option arguments; you
must compare the external variable
optind against the argc
parameter to check this.
If the option has an argument,
getopt returns the argument by
storing it in the variable optarg. You don’t ordinarily need to
optarg string, since it is a pointer into the original
argv array, not into a static area that might be overwritten.
getopt finds an option character in argv that was not
included in options, or a missing option argument, it returns
‘?’ and sets the external variable
optopt to the actual
option character. If the first character of options is a colon
getopt returns ‘:’ instead of ‘?’ to
indicate a missing option argument. In addition, if the external
opterr is nonzero (which is the default),
prints an error message.