Use getopt() & getopt_long() to Parse Arguments

Today I came across a function [getopt] by accident.
It is very useful to parse command-line arguments with this tool!

Here is:

#inlcude <unistd.h>
int getopt(int argc, char * const argv[], const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;

#include <getopt.h>
int getopt_long(int argc, char * const argv[],
                         const char *optstring,
                         const struct option *longopts, int *longindex);
int getopt_long_only(int argc, char * const argv[],
                         const char *optstring,
                         const struct option *longopts, int *longindex);

---

Explain for getopt():

• Arguments argc and argv are the argument count and array as passed to the main() function.
• optstring is the options set. One semicolon following a character means that character need a argument, and two semicolon mean the argument is optional.
• optind is the index of the next element to be processed in argv. The system initializes this value to 1. You can reset it to 1 to restart scanning of the same argv, or when scanning a new argument vector.
• If there are no more option characters, getopt() returns -1 or, it will keep return the ASCII of the current character.
• optarg points to the argument string of one option if that option has argument following.

E.g.

#include <unistd.h>
#include <stdio.h>
#include <stdbool.h> // bool type
/* Macro Definition */
#define NO 0
#define YES 1
#define OK 0
#define ERROR -1

/* Structure for Global Arguments */
struct GlbArgs_t{
    bool version;
    bool help;
    char *number;
    char *type;
}GlbArgs;

/* Options allowed */
static const char *optString = "n:t::vh?";
/* Usage */
static const char *usage = "Usage: \n"
                           "-n\n"
                           "-tx (x=type-name) \n"
                           "-v\n"
                           "-h -?\n";
/* Initialize Global Argument structure */
void InitGlbArg()
{
    GlbArgs.version = NO;
    GlbArgs.help    = NO;
    GlbArgs.number  = NULL;
    GlbArgs.type    = NULL;
}

int main(int argc, char **argv)
{
    int opt = 0; // option

    InitGlbArg();

    while((opt = getopt(argc, argv, optString)) != ERROR){
        switch(opt){
        case 'n':
            GlbArgs.number = optarg;
            printf("Number: %s\n", GlbArgs.number);
            break;
        case 't':
            GlbArgs.type = optarg;
            printf("Type: %s\n", GlbArgs.type);
            break;
        case 'v':
            GlbArgs.version = YES;
            printf("Version: 1.0\n");
            break;
        case 'h':
        case '?':
            printf("%s", usage);
            break;
        default:
            break;
        }
    }

    return OK;
}

• Learn a lot from here
• For more details, refer to [man 3 getopt] (LInux)