C: getopt_long_only Example: Accessing command line arguments

getopt_long is useful to work with the command line arguments. But while working with getopt_long, — is used for long options and – for short options. getopt_long_only accepts both — and – for long options

  1. rectangle -a -l 12 -b 34: will calculate the area of the rectangle
  2. square -p -l 12 -b 34: will calculate the perimeter of the rectangle
  3. rectangle -a -p -l 12 -b 34: will calculate the area and perimeter of the rectangle
  4. rectangle –area –length 12 –breadth 34: will calculate the area of the rectangle
  5. square -perimeter –length 12 –breadth 34: will calculate the perimeter of the rectangle
  6. rectangle -area -perimeter –length 12 –breadth 34: will calculate the area and perimeter of the rectangle

The program is much like getopt_long.

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>

/** Program to calculate the area and perimeter of 
 * a rectangle using command line arguments
 */
void print_usage() {
    printf("Usage: rectangle [ap] -l num -b num\n");
}

int main(int argc, char *argv[]) {
    int opt= 0;
    int area = -1, perimeter = -1, breadth = -1, length =-1;

    //Specifying the expected options
    //The two options l and b expect numbers as argument
    static struct option long_options[] = {
        {"area",      no_argument,       0,  'a' },
        {"perimeter", no_argument,       0,  'p' },
        {"length",    required_argument, 0,  'l' },
        {"breadth",   required_argument, 0,  'b' },
        {0,           0,                 0,  0   }
    };

    int long_index =0;
    while ((opt = getopt_long_only(argc, argv,"", 
                   long_options, &long_index )) != -1) {
        switch (opt) {
             case 'a' : area = 0;
                 break;
             case 'p' : perimeter = 0;
                 break;
             case 'l' : length = atoi(optarg); 
                 break;
             case 'b' : breadth = atoi(optarg);
                 break;
             default: print_usage(); 
                 exit(EXIT_FAILURE);
        }
    }
    if (length == -1 || breadth ==-1) {
        print_usage();
        exit(EXIT_FAILURE);
    }

    // Calculate the area
    if (area == 0) {
        area = length * breadth;
        printf("Area: %d\n",area);
    }

    // Calculate the perimeter
    if (perimeter == 0) {
        perimeter = 2 * (length + breadth);
        printf("Perimeter: %d\n",perimeter);
    }
    return 0;
}
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