Example using command line arguments

If your program needs command line arguments in order to run, then you should have a clearly marked usage instructions in your file header comment to explain how to run the program.

/**********************************************
* File: exampleargs.c
* Author: S. Bogar
* Date: ??
* Modified: 9/26/05
* Section: 0101
* Email: bogar@cs.umbc.edu
* 
* A program to demonstrate the use of command-line 
* arguments. It demonstrates how to open files and 
* do some error-checking
***********************************************/

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

int main(int argc, char** argv) 
{
   FILE *ifp, *ofp;

   /* check that the number of arguments on the command line
   *  is correct */
   if (argc != 3)
   {
      fprintf (stderr, "This program requires command line arguments\n");
      fprintf (stderr, "that are the name of the input file to be\n");
      fprintf (stderr, "used, and the name of the output file to\n");
      fprintf (stderr, "be used\n");
      exit (-1);
   }

   /* open the input file */
   ifp = fopen (argv[1], "r");
   if (ifp == NULL)
   {
      fprintf(stderr, "Sorry, couldn't open input file:\n");
      fprintf(stderr, "%s\n", argv[1]);
      exit (-2);
   }

   /* open the output file */
   ofp = fopen (argv[2], "w");
   if (ofp == NULL)
   {
      fprintf(stderr, "Sorry, couldn't open output file:\n");
      fprintf(stderr, "%s\n", argv[2]);
      exit (-3);
   }

    .
    .
    .

}