pipe output loaded into an array

ygloo · 11-16-2006, 08:17 AM

hello,
i took a look at opendir/readdir/closedir function...
question is how to parse the stream, so that every dir/file becomes an array member.

osvaldomarques · 11-16-2006, 04:50 PM

Hi Ygloo,

The popen command works just like the fopen. It just opens a pipe and you have to treat it as a text file; that means, you have to "fgets" the contents of the stream into your program and treat each record as a line in your program. The strtok must be used for each field after read the record.
Another thing to note is you are thinking of the tabulated ls, with various files per line. When you execute ls for other output than the console, you'll get the option "-1", which means one file per line.

Last but not least, use the strtok very carefully as it is the once function I know which destroys the source variable because it replaces the delimiter with a null character; also it has an static pointer which stores the position of the next operation. This means you cannot use 2 strtoks at the same time in your program.

ygloo · 11-16-2006, 06:39 PM

read in a c_tutorial that "fgets" is obsolete... (suggested is "getline")
i made it to the point where script reads from pipe and "strtok" parses the output with delimiter "\n" (newline), so i get directory list...

howto load this data into an array??
i wonder what to do with array size ( every dir has different number of files in it)
one idea is to count how many tokens "strtok" is producing and then to initialise the array...

tux has to think... ... ...

ygloo · 11-16-2006, 06:44 PM

Code:


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

int main()
{
  char delims[] = "\n";
  char *result = NULL;
  FILE *ls_pipe;
  int bytes_read;
  int nbytes = 100;
  char *my_string;


  /* Open pipe */
  ls_pipe = popen ("ls", "r");
  
  /* Check that pipe is non-null, therefore open */
  if (!ls_pipe)
    {
      fprintf (stderr,
               "pipe failed.\n");
      return EXIT_FAILURE;
    }

  /* These 2 lines are the heart of the program. */
  my_string = (char *) malloc (nbytes + 1);
  bytes_read = getdelim (&my_string, &nbytes, "\n", ls_pipe);

  if (bytes_read == -1)
    {
      puts ("ERROR!");
    }
  else
    {
      result = strtok( my_string, delims );
         while( result != NULL )
	    {
               printf( "%s\n", result );
               result = strtok( NULL, delims );
            } 
	          
    }
   
  return 0;
}

osvaldomarques · 11-16-2006, 07:02 PM

Hi Ygloo,

I don't want to flame about fgets and getline but getline is not an ANSI C standard. And both functions serve the same purpose.

Your problem must be resolved with dynamic memory allocation; you need to control the memory available and check if there is enough. Here you should look for "linked lists". The functions you'll need are malloc and free.

The beauty of this language is that there are zillions of ways to obtain the job done.

That is the beginning of the memory leaks in your life.