Re: dynamic array of ints

From: Robert Strandh (strandh_at_labri.fr)
Date: 07/28/04 

Date: 28 Jul 2004 21:29:17 +0200

"John Hanley" <jdhanley@telusplanet.net> writes:

> I have an interesting problem and I'm not sure the best way to do this.
>
> I am reading in a variable number of integers from a file (eg. 001 002 003
> 004 012 015). At compile time I have no idea how many will be there. But I
> need to parse them out and put them in an array.
>
> I could do an fscanf and just read until '\n', however I won't know how many
> are there and thus don't know how large to make my array.
>
> I could read it in as one large string, traverse through and count the
> number of ints and then allocate memory based on that. However I am not
> sure what to use to read the ints from the string. sscanf works but
> multiple calls to it start at the beginning of the string each time. And
> it seems like a sloppy way to do things anyway.
>
> Are there any suggestions as to what approach to take with this? I wanted
> to avoid using a link list as it seems like alot of work for maybe less than
> 10 ints I need to parse out.
>
> Suggestions? Ideas?

You could do it recursively. Code not tested:

int *
read_ints(FILE *stream, int n, int *how_many)
{
  if(end_of_line(stream))
    {
      *how_many = n;
      return malloc(n * sizeof(int));
    }
  else
    {
      int number = read_int(stream);
      int *result = read_ints(stream, n + 1, how_many);
      result[n] = number;
      return result;
    }
}

...

int
main(void)
{
  FILE *stream = ...;
  int how_many;
  int *numbers = read_ints(stream, 0, &how_many);
  ...
} 

-- 
Robert Strandh
---------------------------------------------------------------------
Greenspun's Tenth Rule of Programming: any sufficiently complicated C
or Fortran program contains an ad hoc informally-specified bug-ridden
slow implementation of half of Common Lisp.
---------------------------------------------------------------------

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