From:	"John M. Aldrich" <fighteer AT cs DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Dynamic Arrays
Date:	Mon, 20 Jan 1997 21:26:58 -0800
Organization:	Two pounds of chaos and a pinch of salt
Lines:	74
Message-ID:	<32E453A2.FA3@cs.com>
References:	<01bc072e$33eb9b20$ee038cd0 AT wahander>
Reply-To:	fighteer AT cs DOT com
NNTP-Posting-Host:	ppp211.cs.com
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

Josh Anderson wrote:
> 
> I know this is a stupid question, but how do you create a dynamic array of
> a bunch of structs? I only need to set the size of the array at init time.
> And then free the memory at exit.

Any basic C textbook should explain how to do this.  It's a standard
part of learning the language.  A detailed explanation would be more
appropriate to one of the C newsgroups (comp.lang.c for example), but
I've broken this rule in the past and I will continue to do so in the
future.  :)

If you want to create an array of _fixed_ size at initialization, then
the task is extremely simple.  First, define your struct.  Then create
a pointer to that struct type and malloc the appropriate amount of memory.
You can then access the pointer exactly like you would an array.  When
you are ready to exit, just call free() with the original pointer.

Example code:

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

struct stuff
{
    int id;
    char name[20];
    char type;
    time_t date_in;
    time_t date_out;
};

int main( void )
{
    struct stuff *List;
    int num_recs, i;

    printf( "How many records?  " );
    scanf( "%d", &num_recs );

    List = (struct stuff *) malloc( num_recs * sizeof(struct stuff) );
    if ( List == NULL )
    {
        fprintf( stderr, "Fatal error:  could not allocate %d bytes.\n",
                 num_recs * sizeof(struct stuff) );
        exit( 1 );
    }

    for ( i = 0; i < num_recs; i++ )
    {
        get_record( List[i] );
        do_stuff( List[i] );
    }

    printf( "All done, thanks.\n" );
    free( List );
    return 0;
}

If you want to make the entire list dynamic, i.e.; its size can change
during runtime, then you need a much more complex algorithm, but again
it's something that's in every C textbook I've ever seen.  If you really
still need help, email me in private and I'll send you more samples.

Good luck!

-- 
---------------------------------------------------------------------
| John M. Aldrich, aka Fighteer I  |        fighteer AT cs DOT com         |
| "Starting flamewars since 1993"  |   http://www.cs.com/fighteer   |
|  *** NOTICE ***  This .signature is generated randomly.           |
|                  If you don't like it, sue my computer.           |
---------------------------------------------------------------------

- Raw text -