[Sussex] C programming help

[Captain Redbeard]

Hi all,

I've just spent the last 48 hours (I think I remember getting some sleep 
somewhere) trying to get a C program that I'm coding to work.  I'm not a 
trained programmer, just amateur stuff, library books, things like that 
but the program uses some fairly advanced concepts like function 
pointers, arrays of structures, etc.  The program (a miniature ecosystem 
simulator) has pretty much all of the functionality coded into it that I 
want however I keep running into run-time crashes like "segmentation 
faults" and more bafflingly "*** glibc detected *** double free or 
corrupted (!prev):" and variations on this.  I suspect that the problem 
comes from mishandling pointers and malloc()/free() statements, 
traceable probably to a deeper misunderstanding of how memory allocation 
works in C.  Does anybody know of any good forums where learner/newbie 
programmers can get help with this sort of thing?  None of the 
tutorials/books I found delve deeply enough into the kind of concepts 
mentioned enough to be of use and Googling for the error messages only 
gives errors in specific applications without explaining exactly what 
"*** glibc detected ***" actually means.  On the other hand if there are 
any C programmers on this mailing list who would be willing to help me 
out then let me know and I can post some short example programs here.  
I've been working on the program every evening for about two weeks now 
and have a LOT of backlogged questions.

Here is an example of what I am running into.  As far as I know the 
following program should be syntactically correct.  It compiles OK but 
when I run it I get a "Segmentation fault" error.  Why?

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

// Set up a coordinate structure
struct Coords
{
  int X;
  int Y;
};

// Set up an array of structures (???)
struct Coords **CoordArray;

int main()
{
  // Initialises the first element of the array
  CoordArray[0] = malloc (sizeof (struct Coords));

  return 0;
}
========================================

Note: if it makes any difference, I'm using GCC version 3.3.4 under 
Slackware 10.2 using the command "gcc -Wall -o malloctest malloc.c".

Any ideas anyone?



Captain Redbeard.


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