Thread: reading in command line arguments from a file?

>your code( while well over my head)compiles fine but crashes the program
>your code (I can grasp some of it) runs great until the args in the file exceed four

Who's code are you referring to?

The problem with citizen's code is that he's not allocating memory for the argv array, that's why it crashes.

I really appreciate the understanding and patience as I'm learning and very ignorant when it comes to dealing with buffers,pointers,allocating memory...I've only had one very basic c++ class. And we only made it to arrays,every thing else I've learned I've looked for,hunted for,googled for, and asked about...passed my professor up long time ago..so he has not been much help as of late, but he did get me hooked on programming.

But why cant I exceed four args with your code,bivhitscar. Cause I hate to use something I dont understand...

citizen, as Im learning and dont fully understand what is going on yet. pity not. I just am not good enough yet to see the genius in what your coding...but Im trying to learn.

You should be able to ue more than four arguments with my code, it worked with six for me.

Can you post your current usage?


[EDIT]

Crap, I am trying it with more args now and it's crashing, I'll try to find the error...

Why don't you just use my code? Mine works just fine:

Code:

itsme@itsme:~/C$ ./addargs *.c
argv[0] = ./addargs
argv[1] = 1kfile.c
argv[2] = abspath.c
argv[3] = addargs.c
argv[4] = afternum.c
...
argv[233] = wrap.c
argv[234] = zero.c
argv[235] = -b
argv[236] = -B
argv[237] = 999
argv[238] = -s
argv[239] = -vv
argv[240] = -R
itsme@itsme:~/C$

It's frustrating when I try to help someone and they totally disregard my statement that another program won't work as-is, and tries it anyway and then discovers (gasp!) it doesn't work. And it's doubly frustrating when I write a working program and someone totally disregards it. You'll be lucky to get help from me again.

FYI, bv, one of your errors:

Code:

                        arg[argc - 1] = malloc( sizeof( arg ) );
                        arg[argc - 1] = position;

You're allocating a pointer's worth of memory and then losing it right on the next line. Did you mean this instead?

Code:

arg[argc - 1] = malloc(strlen(position) + 1);
strcpy(arg[argc - 1], position);

Nah, I was thinking about it the wrong way. I only wanted an array of pointers (to buf, in this case) - I got a bit confused.

And I just wrote out a whole new version, even after reading through yours because I thought it wasn't using argv - again, confusion on my part.

As it took me so long, I just have to post it:

Code:

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

int main(int argc, char **argv)
{
    FILE * file;
    char buf[BUFSIZ], tmp[BUFSIZ];
    char *position;
    char ch;
    int i, j, offset = 0;

    if ( argc == 1 )
    { 
         if ( (file = fopen("args.txt", "r")) == NULL )
         {
              exit(1);
         }
         else
         {
             if ( fgets( buf, BUFSIZ, file ) != NULL )
             {
                  position = strtok( buf, " " );
                  
                  while ( (position = strtok( NULL, " " )) != NULL )   
                  {
                        argc++;
                  }     
                  
                  argv = malloc( argc );
                  
                  for ( i = 0; i < argc; i++ )
                  {
                      argv[i] = malloc( strlen( &buf[offset] ) + 1 );
                      strcpy( argv[i], &buf[offset] );
                      offset += strlen( &buf[offset] ) + 1;
                  }
                  argv[argc] = NULL;
             }
         }
    }
    
    ch = getchar();
    
    return 0;
}

Code:

argv = malloc( argc );

That line is still wrong. You're going to have to multiply argc by the size of a pointer to have enough room.

Also, I think you're going to end up with a '\n' at the end of the last added arg (from the fgets() input).

You're correct itsme, about the newline. And I had a feeling the line you mentioned was wrong too. Should it be argv = malloc ( argc * sizeof( argv ) )?

close...just change sizeof( argv ) to sizeof( *argv ). The one you posted will work, but just by chance.

Cool bananas, thanks mate.

Looking over some of the code I've written makes me realise how much I've actually learnt in the past six months. Definitely helped along by people like youself and salem and co.