arrays with different sizes..

i want to define arrays with different sizes..

something like this..

Code:

---

struct block{
        int id;
        int points[3];
        int cells[3];
        struct covar covariant[cells[0]][cells[1]][cells[2]];
};

---

however since cells is defined inside the same structure i cannot define it like this..
what is the way out??

Dynamic memory allocation would be one option. Look at the malloc() function.

can you elaborate..
afaik malloc is used for pointers..
i couldnt find its use to initialize arrays...

You can simulate an array using malloc():

Code:

---

{
int size;
int *array;

size = 5;

array = malloc(sizeof(int) * size);
// Now you can access array[0] through array[4].
free(array);
}

---

hey thanks that worked.. but i am unable to rewind the pointer.. how do i do that?

Rewind the pointer? I'm assuming you're doing something like:

Code:

---

{
  char *ptr = malloc(10);

  strcpy(ptr, "foo");
  while(*ptr)
  {
    putchar(*ptr);
    ptr++;
  }
  // Uh oh! I lost the original start of the memory allocation
}

---

If that's what you mean then there's no way to get it back. The way to handle that situation correctly is to leave a pointer pointing to the beginning and don't change it. Use a second pointer to walk around instead.

hi.. i ve been rtying to do what u said..
but it gives me segmentation fault as soon as i try to declare another pointer..
am i missing something here..

I mean something like this:

Code:

---

{
  char *ptr, *ptr2;

  ptr = malloc(10);

  strcpy(ptr, "foo");
  ptr2 = ptr;

  while(*ptr2)
  {
    putchar(*ptr2);
    ptr2++;
  }

  free(ptr);
}

---

Maybe you could post the code you're actually trying and I or someone else can find the problem.

yes i got what you were trying to say..
but i just found that declaring any more pointers in my program causes seg. fault...
here's the code...
if i delelte any one of the colored part the seg. fault goes away ..
otherwise however.. any pointer declaration gives an error..
i have a 768 mb ram on my comp.. could it be a memory problem??

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "structures.c"

int main()
{
FILE *stream;

if((stream=fopen("block2.dat","r"))!=NULL){
        printf("Succesfully opened file\n");
}
else{
        printf("Failed to open file\n");
        exit(1);
}

char number[5];char temp[10];

char num_i[5],num_j[5],num_k[5];
int j=0;int k=0;int i=0;int l,m,z,loop_var;

fscanf(stream,"%s", number);
num_blocks=atoi(number);
printf("%i\n",num_blocks);
struct block arr_blocks[num_blocks];
int no_i,no_j,no_k,total_points;

for(i=0;i<num_blocks;i++){
        fscanf(stream,"%s        %s        %s", num_i,num_j,num_k);
        arr_blocks[i].id=i;
        arr_blocks[i].points[0]=atoi(num_i);
        arr_blocks[i].points[1]=atoi(num_j);
        arr_blocks[i].points[2]=atof(num_k);
        arr_blocks[i].cells[0]=(atoi(num_i))-1;
        arr_blocks[i].cells[2]=(atoi(num_j))-1;
        arr_blocks[i].cells[1]=(atoi(num_k))-1;
}

struct point *p_map,*p_map_2;
struct covar ***p_covariant[num_blocks];
struct contra ***p_contravariant[num_blocks];

for(loop_var=0;loop_var<num_blocks;loop_var++){
        total_points=(arr_blocks[loop_var].points[0])*
                                (arr_blocks[loop_var].points[1])*(arr_blocks[loop_var].points[2]);

        //allocating memory for covar
        p_covariant[loop_var]=
                (struct covar***)malloc(sizeof(struct covar**)*((arr_blocks[i].cells[0])));
        for (i=0; i<(arr_blocks[i].cells[0]); i++)
        {
                p_covariant[loop_var][i] =
                (struct covar**)malloc(sizeof(struct covar*)*(arr_blocks[loop_var].cells[1]));
                for (j=0; j<(arr_blocks[loop_var].cells[1]); j++)
                {
                        p_covariant[loop_var][i][j] =
                                (struct covar*)malloc(sizeof(struct covar)*
                                        (arr_blocks[loop_var].cells[2]));
                }
        }

        **p_covariant[loop_var]=&p_covariant[loop_var][0][0][0];

        p_contravariant[loop_var] = (struct contr..........*)malloc(sizeof(struct contr..........)*
                                        (arr_blocks[i].cells[0]));
        for (i=0; i<(arr_blocks[i].cells[0]); i++)
        {
                p_contravariant[loop_var][i] =
                (struct contr..........)malloc(sizeof(struct contra*)*(arr_blocks[loop_var].cells[1]));
                for (j=0; j<(arr_blocks[loop_var].cells[1]); j++)
                {
                        p_contravariant[loop_var][i][j] =
                        (struct contra*)malloc(sizeof(struct contra)
                                                *(arr_blocks[loop_var].cells[2]));
                }
        }
        **p_contravariant[loop_var]=&p_contravariant[loop_var][0][0][0];

        //Read all the co-ordinates from the file
        p_map=(struct point*)malloc(sizeof(struct point)*total_points);
        printf("%u\n",p_map);
        p_map_2=p_map;
        printf("%u\n",p_map_2);
        j=0;k=0;
        for(k=0;k<3;k++){
                for(i=0;i<total_points; i++){
                        fscanf(stream,"%s",temp);
                        (*p_map).coords[k]=atof(temp);
                        p_map++;
                }
        }
}
return 0;
}

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