getopt

#include <stdio.h> //for printf
#include <stdlib.h> //for exit
#include <unistd.h>
#include <getopt.h>

void print_help(){
	puts("srun [-N nodes] [-n tasks] executable\n\
			-N 		number of nodes\n\
			-n 		number of tasks\n\
			-h --help	print the help");
}
/*
	not all argv are options, an element of argv that starts with '-' is an option
	//If getopt() is called repeatedly, it returns successively each of
	//the option characters  from  each  of the option elements.

	#include <unistd.h>
	int getopt(int argc, char * const argv[], const char *optstring);
	extern char *optarg;  //pointer the parameter of an option
	extern int optind;  //indicate the position of argv to help the next call getopt() which can resume the scan
	extern int opterr;  //if opterr is set to 0 (i.e., opterr = 0;), the calling program will prevent the error message
	extern int optopt;
	//If getopt() does not recognize an option character, it prints an error message to stderr,
	 stores the character in optopt, and returns ’?’.
*/
void get_opt_in_short(int argc, char **argv){
	//If a character is followed by a colon, the option requires an argument
	//Two colons mean an option takes an optional arg
	const char *short_options = "N:n:i::h";
	int opt;
	opterr = 0;
	while((opt = getopt(argc, argv, short_options)) != -1){
		switch(opt){
		case 'N':
			printf("Node -N, optarg = %s\n", optarg);
			break;
		case 'n':
			printf("Task -n, optarg = %s\n", optarg);
			break;
		case 'i':
			if(!optarg)
				puts("Nict to meet you!");
			else
				printf("Nict to meet you! %s\n", optarg);
			break;
		case 'h':
			print_help();
			break;
		case '?':
			printf("can't recognize, the optopt = %c\n", (char)optopt);
			break;
		default:
			break;
		}
		printf("optind = %d\n", optind);
	}
	//If  there  are  no more option characters, getopt() returns -1.
	//Then optind is the index in argv of the first argv-element that is not an option.
	printf("after scan, optind = %d\n", optind);
}

int main(int argc, char **argv){
	get_opt_in_short(argc, argv);
	return 0;
}