getopt

useful link: https://www.gnu.org/software/libc/manual/html_node/Using-Getopt.html

it is from header file unistd.h which must be included

int opterr

default is nonzero, when parse unknow options or miss argument, it would panic

set to zero to make your own behavior.

int optopt

use with opterr, get the option character

int optind

option character index which from 1 to start, end when option return -1

use with argc to check if non-option argument begin

char *optarg

option argument

int getopt

int main(int argc, char *argv[]){
    int c;
    while((c = getopt(argc, argv, "abc:")) != -1) {
        switch(c) {
        case 'a':
            break;
        //
        }
    }
}