getopt - is it possible to use getopt_long to parse arrays of strings similar to command line arguments in a C program? -

i aware getopt should used parse command line arguments, , not strings.

however, confused fact if pass array of strings "looks like" argv variable, getopt_long seems work, only first time call it. second, , subsequent times, call it ignores arguments , returns default ones.

the reason doing turning application used take command line arguments in "interactive" version of asks user arguments, actions based on arguments, asks more arguments , on.

the following code minimal example reproduces error

#include <stdio.h> #include <stdlib.h> #include <getopt.h>  struct input_parameters{     char * d; // data set };  int solver_help(int argc, char* const argv[], struct input_parameters * p) {   int c;    p->d = "default name";    while (1)   {       static struct option long_options[] =       {           {"data",  required_argument,     0, 'd'},           {0, 0, 0, 0}       };       /* getopt_long stores option index here. */       int option_index = 0;        c = getopt_long (argc, argv, "d:",                        long_options, &option_index);        /* detect end of options. */       if (c == -1)         break;        switch (c)       {           case 'd': p->d = optarg;               break;           default:               printf("wrong option specification\n");               exit(-1);       }   }    return 0 ;   }       int main () {      int argc_first = 3;     char * const argv_first[] = { "getopt_test", "--data", "first" };     struct input_parameters first_input;     solver_help(argc_first, argv_first, &first_input);      printf("i think data is: %s\n", first_input.d);      int argc_second = 3;     char * const argv_second[] = { "getopt_test","--data", "second" };     struct input_parameters second_input;     solver_help(argc_second, argv_second, &second_input);      printf("i think data is: %s\n", second_input.d);      return 0; } 

the output of code is

i think data is: first think data is: default name 

from manual page getopt:

in order use getopt() evaluate multiple sets of arguments, or evaluate single set of arguments multiple times, variable optreset must set 1 before second , each additional set of calls getopt(), , variable optind must reinitialized.

modifying code gives desired results:

#include <stdio.h> #include <stdlib.h> #include <getopt.h>  struct input_parameters {     char * d; // data set };  int solver_help(int argc, char* const argv[], struct input_parameters * p) {     p->d = "default name";      static struct option long_options[] =     {         {"data",  required_argument,     0, 'd'},         {0, 0, 0, 0}     };      int option_index = 0;      optreset = 1;     /*  add  */     optind = 1;       /*  add  */      int c = getopt_long(argc, argv, "d:",                         long_options, &option_index);      switch ( c )     {         case -1:             break;          case 'd':             p->d = optarg;             break;          default:             printf("in default case...\n");             printf("wrong option specification\n");             exit(exit_failure);     }      return 0; }      int main(void) {      int argc_first = 3;     char * const argv_first[] = { "getopt_test", "--data", "first" };     struct input_parameters first_input;     solver_help(argc_first, argv_first, &first_input);      printf("i think data is: %s\n", first_input.d);      int argc_second = 3;     char * const argv_second[] = { "getopt_test","--data", "second" };     struct input_parameters second_input;     solver_help(argc_second, argv_second, &second_input);      printf("i think data is: %s\n", second_input.d);      return 0; } 

with output:

paul@horus:~/src/sandbox$ ./go think data is: first think data is: second paul@horus:~/src/sandbox$