iget long options from command line argument list 



#include <getopt.h>

extern char *optarg;

extern int optind;

extern int optopt;

extern int opterr;

extern int optreset;

int getopt_long(int argc, char * const *argv, const char *optstring, const struct option *longopts, int *longindex);


The getopt_long() function is similar to getopt() but it accepts options in two forms: words and characters. The getopt_long() function provides a superset of the functionality of getopt(). The getopt_long() function can be used in two ways. In the first way, every long option understood by the program has a corresponding short option, and the option structure is only used to translate from long options to short options. When used in this fashion, getopt_long() behaves identically to getopt(). This is a good way to add long option processing to an existing program with the minimum of rewriting.

In the second mechanism, a long option sets a flag in the option structure passed, or will store a pointer to the command line argument in the option structure passed to it for options that take arguments. Addition with an equal sign, e.g.,

myprogram --myoption=somevalue

When a long option is processed, the call to getopt_long() will return 0. For this reason, long option processing without shortcuts is not backwards compatible with getopt().

It is possible to combine these methods, providing for long options processing with short option equivalents for some options. Less frequently used options would be processed as long options only.

The getopt_long() call requires a structure to be initialized describing the long options. The structure is:

struct option 
    char *name;
    int has_arg;
    int *flag;
    int val;

The name field should contain the option name without the leading double dash.

The has_arg field should be one of:

no argument to the option is expected
an argument to the option is required
an argument to the option may be presented

If flag is not NULL, then the integer pointed to by it will be set to the value in the val field. If the flag field is NULL, then the val field will be returned. Setting flag to NULL and setting val to the corresponding short option will make this function act just like getopt().

If the longindex field is not NULL, then the integer pointed to by it will be set to the index of the long option relative to longopts.

The last element of the longopts array has to be filled with zeroes.


If the flag field in struct option is NULL, getopt_long() return the value specified in the val field, which is usually just the corresponding short option. If flag is not NULL, these functions return 0 and store val in the location pointed to by flag. These functions return `:' if there was a missing option argument, `?' if the user specified an unknown or ambiguous option, and -1 when the argument list has been exhausted.


If set, option processing stops when the first non-option is found and a leading `-' or `+' in the optstring is ignored.


     int bflag, ch, fd;
     int daggerset;

     /* options descriptor */
     static struct option longopts[] = {
         { "buffy", no_argument, NULL, 'b' },
         { "fluoride", required_argument, NULL, 'f' },
         { "daggerset", no_argument, &daggerset, 1 },
         { NULL, 0, NULL, 0 }

     bflag = 0;
     while ((ch = getopt_long(argc, argv, "bf:", longopts, NULL)) != -1) {
         switch (ch) {
             case 'b':
                 bflag = 1;
             case 'f':
                 if    ((fd = open(optarg, O_RDONLY, 0)) == -1)
                     err(1, "unable to open %s", optarg);
             case 0:
                 if (daggerset) {
                     fprintf(stderr,"Buffy will use her dagger to "
                     "apply fluoride to dracula's teeth\n");
     argc -= optind;
     argv += optind;






This section describes differences to the GNU implementation found in glibc-2.1.3:


Setting of optopt for long options with flag != NULL:


sets optopt to val.

NuTCRACKER Platform 

sets optopt to 0 (since val would never be returned).


Setting of optarg for long options without an argument that are invoked via '-W' ('W;' in option string):


sets optarg to the option name (the argument of `-W').

NuTCRACKER Platform 

sets optarg to NULL (the argument of the long option).


Handling of '-W' with an argument that is not (a prefix to) a known long option ('W;' in option string):


returns '-W' with optarg set to the unknown option.

NuTCRACKER Platform 

treats this as an error (unknown option) and returns '?' with optopt set to 0 and optarg set to NULL (as GNU's man page documents).


NuTCRACKER Platform does not permute the argument vector at the same points in the calling sequence as GNU does. The aspects normally used by the caller (ordering after -1 is returned, value of optind relative to current positions) are the same, though. (We do fewer variable swaps.)


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