Thread: trouble understanding file option and command line arguments

Hi,

I am creating a program with the C language that simulates the WC command in Unix. My program needs to count lines, bytes and words. I have not added the code to count bytes and words yet. I am having trouble understanding what the file option/flag '-' does. I can not visualize how it moves through program code. argc and argv look at one line at a time and they only look at what is on the command line. I am not sure how a program is broken up into files for WC to read.

this is the code I have so far:

Code:

/* wc simulate */

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

char *pgmname; /* name of this program */

int line_count = 0;
int word_count = 0;
int byte_count = 0;

FILE *fp;

void main(argc, argv)

int argc; char *argv[];
{


int i;
char *cp;

pgmname = argv[0];
fp = stdin;

for(i = 1; i < argc; i++) {
        cp = argv[i];
        if(*cp == '-'){
                if(*++cp == '\n'){
                        line_count++;}
                
                
        }

        else {
                  if(fp != stdin) {
                   fprintf(stderr, "%s: too many arguments\n", pgmname);
                   exit(1);
                }

                fp = fopen(cp, "r")
                if(fp == NULL) {            
                   fprintf(stderr, "%s: unable to read %s\n", pgmname, cp);
                   exit(1);
                }

        }

                printf("%d\n", line_count);
}

                

}

Right now I have code to just count the lines. I am testing the program on a hello world program below:

Code:

#include <stdio.h>

main()
{
printf("Hello World!\n");
}

when I test the program, I get 0 for line count.

Use getopt() in unistd.h, it takes care of argument parsing and gives more flexibility than doing it by hand.

Originally Posted by dsemel

Hi,

I am creating a program with the C language that simulates the WC command in Unix. My program needs to count lines, bytes and words. I have not added the code to count bytes and words yet. I am having trouble understanding what the file option/flag '-' does. I can not visualize how it moves through program code. argc and argv look at one line at a time and they only look at what is on the command line. I am not sure how a program is broken up into files for WC to read.

Code:

/* wc simulate */

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

char *pgmname; /* name of this program */

int line_count = 0;
int word_count = 0;  <--- these don't need to be global
int byte_count = 0;          move them inside main()
FILE *fp;



void main(argc, argv)  <--- int main (int argc, char* argv[])

int argc; char *argv[];  <--- delete this

{

The remainder of the code is not very well thought out...

You need to designate one of the argv[] strings as the filename to be parsed. From there fopen() the file, use fgets() to read it in line by line and do whatever you need to do to the text.

You don't actually care what the name of your program is.

Detecting flags is pretty easy...

Code:

if (argv[2][0] =='-')
  flag = argv[2][1]);

from there you just parse your flags or remember them to use in conditionals in your program..

thank you for your reply.

does argv need to be intialized as a 2 dimensional array?

argv[2][0] is 2 the argument number and 0 the current line?

thanks again!

Originally Posted by dsemel

thank you for your reply.

does argv need to be intialized as a 2 dimensional array?

argv[2][0] is 2 the argument number and 0 the current line?

thanks again!

You don't initialize argc and argv to anything... they are passed into your main() function by the operating system. To initialize them would be to destroy their contents.

Originally Posted by CommonTater

Detecting flags is pretty easy...

Code:

if (argv[2][0] =='-')
  flag = argv[2][1]);

from there you just parse your flags or remember them to use in conditionals in your program..

It kind of depends, let's say you have 10 flags where half of them takes an argument, and you want to be able to use them in any order. Then it makes sense to look into getopt() IMO, it's a good function to learn if you plan to create command line tools on *nix platforms IMO. Especially if you also want to incorporate them in shell scripts, then you would want them to behave like the rest. Perhaps it's not absolutely necessary in this case but, it's still a good function to know about.

I have this code that I was working on before, and left out from my first post. (I'm new to this)

Code:

#include <stdio.h>

short bflag = 0;
short xflag = 0;

FILE *fp;

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

int i; char *cp;

fp = stdin;

for(i =1; i < argc; i++) {

cp = argv[i];
if (*cp == '-') {   /* a flag */
   
         if(*++cp == 'b')
              bflag++;

         else if(*++cp = 'x')
                xflag++;
}

I've seen programs with switch statements where there are cases with letters. I don't know where the case letters come from.

What do you do when the flag letters are added up?

Where are you getting this garbage code from?

I think what you really need to do is spend some time with your text book and read up on command line arguments... Your approach to this is just wrong.

Command Line Arguments in C - Cprogramming.com

What do you do when the flag letters are added up?

Well in this case, I'd sing Cumbia and make s-mores...

I appreciate your help CommonTater. My books have not been helpful at all with accessing command line arguments. Are there any texts you could recommend? thanks!

Hi CommonTater, I am not being sarcastic. In case it came off that way. I have A Book On C and Unix System Programming by Haviland and accessing command line arguments are not discussed.

I have a Book On C by Ira Pohl and the Unix System programming. There just okay but they don't cover this.

Duh!

Oh by the way, I got that garbage code from my Professor!

Originally Posted by dsemel

Duh!

Oh by the way, I got that garbage code from my Professor!

I think you don't want to hear my response to that!