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From:	pete <pfiland AT mindspring DOT com>
Newsgroups:	comp.lang.c,comp.os.msdos.djgpp
Subject:	Re: Pointer Blues
Date:	Mon, 21 Jan 2002 09:28:16 -0500
Organization:	PF
Lines:	118
Message-ID:	<3C4C2580.6F2C@mindspring.com>
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To:	djgpp AT delorie DOT com
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Jake wrote:
> 
> Pointers are begining to drive me crazy.
> Ok here's the problem, I needed two 2 dimensional arrays that are visual to
> all
> the functions. So I defined two 'pointer-to-pointer' varibles of type int,
> thats what 2 dimensional arrays really are, 'pointers-to-pointer' right?
> That problem is the that whatever value I asign to one array shows up in the
> array, I can have have this.
> If someone can follow the code and know whats going on please help me out.
> 
>       thanks
>        Jake
> #include <stdio.h>
> int columns = 8;
> int rows = 8;
> int **map;
> int **mask;
> void initarray(int **arr);  // allocates memory
> void display(int **arr);
> int main(int argc, char *argv[])
> {
>   int x,y;
>   initarray(map);
>   initarray(mask);
>   for ( y = 0; y < rows;y++)
>     for (x=0;x<columns;x++){
>       map[x][y] = x;
>       mask[x][y] =x*2;
>     }
>   display(map);
>   display(mask);
>   return 0;
> }
> 
> void display(int **arr)
> {
>  int x,y;
>  for (y=0; y<rows; y++){
>    for (x=0; x < columns; x++)
>      printf("%3d",arr[x][y]);
>    puts("");
>  }
>  puts("");
> }
> 
> void initarray(int **arr)
> {
>  int x;
>   for (x=0;x<columns;x++)
>     arr[x] = (int *)calloc(rows, sizeof(int));
> }

/* BEGIN new.c */

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

int **initarray(int, int); 
void display(int **, int, int);

int main(void)
{
    int x, y, **map, **mask, columns, rows;

    columns = 16;
    rows = 8;
    map = initarray(columns, rows);
    mask = initarray(columns, rows);
    for(y = 0; y < rows; ++y){
        for(x = 0; x < columns; ++x){
            map[x][y] = x + y;
            mask[x][y] = map[x][y] * 2;
        }
    }
    display(map, columns, rows);
    free(map);
    display(mask, columns, rows);
    free(mask);
    return 0;
}

void display(int **arr, int columns, int rows)
{
    int x, y;
    
    for(y = 0; y < rows; ++y){
        for(x = 0; x < columns; ++x){
            printf("%3d",arr[x][y]);
        }
        puts("");
    } 
    puts("");
}

int **initarray(int columns, int rows)
{
    int x, **arr;
    
    arr = malloc(columns * sizeof(int*));   
    if(!arr){
        fputs("arr allocation failure.\n", stderr);
        exit(EXIT_FAILURE);
    }
    for(x = 0; x < columns; ++x){
        arr[x] = malloc(rows * sizeof(int));
        if(!arr[x]){
            fprintf(stderr, "arr[%i] allocation failure.\n", x);
            exit(EXIT_FAILURE);
        }
    }
    return arr;
}

/* END new.c */

-- 
 pete

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