Thread: getopt option arguments

I am having some trouble writing a program using getopt.

How would i use getopt to accept arguments (2 filenames for each option)?

For example: ./prog -a file.txt

Code:

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

int main(int argc, char *argv[]){
  int optchar;
  

  while((optchar = getopt (argc, argv, "nsvt")) != -1){
    switch(optchar){
    case 'n':
      
      FILE *fp;
      fp = fopen("text.txt, "r");
      if(fp == NULL){
        printf("File couldn't be opened!\n");
      }
        else{
          printf("File opened!\n");
          int c;
          while((c = fgetc(fp)) != EOF){
            if(c == '\n'){
              printf("newline found\n");
            }
            printf("%c", c);
          }
          fclose(fp);
        }

        break;

      case 's':
        printf("case opt s!\n");
        break;

      case 'v':
        printf("case opt v!\n");
        break;

      case 't':
        printf("case opt t!\n");
        break;
      }
    }
    return 0;

you don't really get what option means, do you?
option is one-to-one input, one option w/ one value.
why do you need such of 2 values for one option?
why not use one more extra option for other file?

Code:

./program -s source_file.txt -d destination_file.txt

I am trying to emulate the cat command, so i want to use ./program -a file.txt file.txt

i use this template from here . Example of Getopt - The GNU C Library there is a long option also.

this little program is how i would have done it as a hello world program but i am not sure if there is not a better more nice way of using it. i am still new to this.

Code:

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>


void PrintUsage(const char *progname);
void fcopy(FILE *in,FILE *out);

int  main (int argc, char **argv)
{
       int aflg = 0;
       int bflg = 0;
       char *cval = NULL;
       int index;
       int c;
       const char *progname=argv[0];
       opterr = 0;
       FILE *fp;
	   
       while ((c = getopt (argc, argv, "abc:")) != -1)
       {     switch (c)
             {
                    case 'a': aflg = 1;       break;
                    case 'b': bflg = 1;       break;
                    case 'c': cval = optarg;  break;
                    case '?':
                       if (optopt == 'c')
			{
                           fprintf (stderr," "
                                      "Option -%c requires an argument.\n"
					  " ", optopt);
                       }
			else if (isprint (optopt))
		      {
                           fprintf (stderr, "Unknown option `-%c'.\n", optopt);
                      }
		      else
		     {
                           fprintf (stderr,
                                   "Unknown option character `\\x%x'.\n",
                                   optopt);
                           exit(EXIT_FAILURE);
		    }
					 
                   default:
                   abort (); 
             }    
        }
		
           if(aflg)
	        for (index = optind; index < argc; index++)
	       {
            
			      fprintf(stdout,"Non-option argument %s\n", argv[index]);
				  exit(0);
	       }
		   else if(bflg)
		   {
			   
                   fprintf(stdout,"aflag = %d, bflag = %d, cvalue = %s\n",
                            aflg, bflg, cval);
							exit(0);
           }
		   
		   else if(cval != NULL)
		   {
		     printf("opening file %s \n",cval);
			 if((fp=fopen(cval,"r")) == NULL)
			 {
				     exit(1);
			 }
			 else
			 {
			     
			 	  fcopy(fp,stdout);
		          exit(EXIT_SUCCESS);
             }
		   }
		   
	       else
	       {
	         fprintf(stdout,"%s executing :no options\n",progname); 
	       }
	   
       return 0;
}

void PrintUsage(const char *progname)
{
	 fprintf(stdout,"USAGE:%s [options]\n"
	                "barebones usage help text\n",
			 progname);
}

void fcopy(FILE *in,FILE *out)
{
	int c;
	while((c=getc(in)) != EOF)
	      fprintf(out,"%c",c);
}

option a shows arguments giving
option b shows what flags status is
option c needs as argument which is on thsi case teh file name to open and display on screen.

i made the example slight modified from the page i linked to and use it as a template in my editor.-

ps:sorry if the indent goes when i post. i have indented before i posted. i hope it is working.

I am very sorry, i didn't read about optarg() properly. I was trying to use optarg when what i wanted was non option args for reading 2 files and printing them to stdout.

Thanks cmay.