getopt() function in C programming could use to parse command line options.

Switch statement used to return value from getopt

If takes an argument from the usage, ':' presents.(From the while loop)

Here’s an example what I learned from the class.



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/*
  @author Sehyun Cho

  Salary calculator that do bonuses and raises to a base salary 
  as well as a veterans bump. Taxes will be deducted from the 
  salary as well. Using getopt to parse the command line, to get salary.

  -b: 5000 bonus on top of the salary, adds to the base.
  -r: multiplies the base by percentage and adding up.
  -v: 6000 bonus on top of the salary, adds to the base.
  -t: multiplies the base by percentage and subtracting.
  
  getopt command line below:

  usage: salary [-bv] [-r rnum] -t tnum base

*/

// Headers

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>


// Main fuction

int main(int argc, char **argv)
{	
	// Declare variables

	extern char *optarg;
	extern int optind;
	int c, err = 0;
	int tnum, rnum = 0;
	int tflag = 0;
	int base;
	double rAmount, vBonus, bBonus, tax, salary;

	// Declare usage

	static char usage[] = "usage %s [-bv] [-r rnum] -t tnum value\n";
	// Switch statement - Since 'r' and 't' take argument, ':' contain.

	while ((c = getopt (argc, argv, "vr:bt:")) != -1)
	{
		switch(c)
		{
			case 'v':
				// Assign bonus 6000 if case v

				vBonus = 6000;
				break;
			case 'r':
				rnum = atoi(optarg);
				// Restrict r value in between 2 and 10

				if(rnum < 2 || rnum > 10)
				{
					fprintf(stderr, "%s:Error. The rnum should be between 2 and 10.\n");
					exit(1);
				}
				rAmount = rnum * 0.01;
				break;
			case 'b':
				// Assign bonus 5000 if case b

				bBonus = 5000;
				break;
			case 't':
				tnum = atoi(optarg);
				// Restrict t value in between 5 and 30

				if(tnum < 5 || tnum > 30)
				{
					fprintf(stderr, "%s:Error. The tnum should be between 5 and 30.\n");
					exit(1);
				}
				tflag = 1;
				tax = tnum * 0.01;
				break;
			case '?':
				// case '?' shows marks as an error

				err = 1;
				break;
		}
	}
}