Allocating 4D Array in C

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January 10th, 2013, 07:04 PM

plikokv

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Join Date: Jan 2013

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Allocating 4D Array in C

Howdy,

I'm trying to write out a function within a project to create and allocate memory for a 4-dimensional array of doubles. I've tried many options and so far the best I've gotten was segmentation fault. My project is due this Sunday, so I'm somewhat desperate to figure this out

Here goes the code:

Code:

double ****
super_malloc(long int n1, long int n2, long int n3, long int n4)
{
  double ****vect;
  double *temp1, **temp2, ***temp3;
  int i1;

  if(!(vect = malloc(n1*sizeof(double ***))))
    {
      perror("Error 1");
      return NULL;
    }

  if(!(temp3 = malloc(n1*n2*sizeof(double **))))
    {
      free(vect);
      vect = NULL;

      perror("Error 2");
      return NULL;
    }

  if(!(temp2 = malloc(n1*n2*n3*sizeof(double *))))
    {
      free(vect);
      vect = NULL;
      free(temp3);
      temp3 = NULL;

      perror("Error 3");
      return NULL;
    }

  if(!(temp1 = malloc(n1*n2*n3*n4*sizeof(double))))
    {
      free(vect);
      vect = NULL;
      free(temp3);
      temp3 = NULL;
      free(temp2);
      temp2 = NULL;

      perror("Error 4");
      return NULL;
    }

  for(i1 = 0; i1 < n3; ++i1)
    temp2[i1] = temp1 + i1*n4*sizeof(double);

  for(i1 = 0; i1 < n2; ++i1)
    temp3[i1] = temp2 + i1*n3*sizeof(double *);

  for(i1 = 0; i1 < n1; ++i1)
    vect[i1] = temp3 + i1*n2*sizeof(double **);

  return vect;
}

This function is used in another function which does something along the lines of:

Code:

double ****vect;

...

vect = super_malloc(n1, n2, n3, n4);

Thanks in advance!

January 11th, 2013, 01:28 AM

salem

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You seemed to be on the right track, but your pointer arithmetic at the end seems off.

This is how I usually do this.
Note how all the 'temp' pointer adjustments don't involve any sizeof's, as this is automatically taken care of by the compiler.

Code:

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

int ****alloc ( int maxx, int maxy, int maxr, int maxc ) {
  int *rows = malloc(maxx*maxy*maxr*maxc*sizeof(*rows));
  int **cols = malloc(maxx*maxy*maxr*sizeof(*cols));
  int ***mat = malloc(maxx*maxy*sizeof(*mat));
  int ****result = malloc(maxx*sizeof(*result));
  for ( int x = 0 ; x < maxx ; x++ ) {
    result[x] = mat; 
    mat += maxy;
    for ( int y = 0 ; y < maxy ; y++ ) {
      result[x][y] = cols ; 
      cols += maxr;
      for ( int r = 0 ; r < maxr ; r++ ) {
        result[x][y][r] = rows;
        rows += maxc;
      }
    }
  }
  return result;
}

int main(void)
{
  int rows = 5, cols = 10, width = 15, height = 20;
  int ****matgrid = alloc(width,height,rows,cols);
  for ( int x = 0 ; x < width ; x++ ) {
    for ( int y = 0 ; y < height ; y++ ) {
      for ( int r = 0 ; r < rows ; r++ ) {
        for ( int c = 0 ; c < cols ; c++ ) {
          matgrid[x][y][r][c] = 0;
        }
      }
    }
  }

  // should be another function
  free(matgrid[0][0][0]);
  free(matgrid[0][0]);
  free(matgrid[0]);
  free(matgrid);
  return 0;
}

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