Thread: Pointer and multidimensional arrays

Here is what I want to do:

1. I have two arrays - one with new data and one with old. I effectively want to swap the pointer such that the pointer to the new data points at the old and the new data storage is deleted (i.e. no leaks).
2. I seem to be failing at the syntax stage. Tying up in Knots.
3. I dont wish to copy the elements..I need to save time, hence this pointer version...ideally which should just enavle me to swap between the two.

Thanks

Here is the code I am trying....its not working at it should as the changes are not being reflected.



#############################################

Code:

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


void MC(double ***ptrBeadArray);
void free_2d(double **d, int nx, int ny);

void MC(double ***ptrBeadArray)
{
	int i;
	double **ptrBeadArrayOld = NULL;
	double ****newptr = NULL;
	ptrBeadArrayOld = (double **)malloc(2  * sizeof(double *));
	for (i = 0; i< 2; i++)
	ptrBeadArrayOld[i] = (double *)malloc(3 * sizeof(double));
	
	
	ptrBeadArrayOld[0][0] = 7.0;
	ptrBeadArrayOld[0][1] = 7.0;
	ptrBeadArrayOld[0][2] = 7.0;
	
	
	
	
	ptrBeadArray = &ptrBeadArrayOld;
	//newptr = &ptrBeadArray;
	printf("%f\n",(*ptrBeadArray)[0][2]);
	//free_2d(*ptrBeadArray, 1, 3);
	//free_2d(**newptr, 2, 3);


}


void free_2d(double **d, int nx, int ny)
{
	int x;
	for (x = 0; x < nx; x++) 
	{
		free(d[x]);
	}
	free(d);
}


int main(void)
{
	int i;
	double **ptrBeadArray = NULL;
	ptrBeadArray = (double **)malloc(2  * sizeof(double *));
	for (i = 0; i< 2; i++)
	ptrBeadArray[i] = (double *)malloc(3 * sizeof(double));
	
	ptrBeadArray[0][0] = 1.0;
	ptrBeadArray[0][1] = 2.0;
	ptrBeadArray[0][2] = 3.0;
	
	MC(&ptrBeadArray);
	
	
	printf("%f\n",ptrBeadArray[0][0]);
	
	//free_2d(ptrBeadArray, 2, 3);
	
	return(0);
}

Now I can do it with the following code in the MC routine, but am concerned that the statement I have put in is actually copying the values in the array rather than effecting the pointers.

[code]

*ptrBeadArray = *&ptrBeadArrayOld;
newptr = &ptrBeadArray;
printf("%f\n",(*ptrBeadArray)[0][2]);
//free_2d(*ptrBeadArray, 1, 3);
free_2d(**newptr, 2, 3);

[\code]

guess this is what you want to do

Code:

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


void free_2d(double **d, int nx, int ny);

void MC(double ***ptrBeadArray)  // you have to pass the array dimensions
{
	int i;
	double **ptrBeadArrayOld = NULL;
	
        ptrBeadArrayOld = (double **)malloc(2  * sizeof(double *));
	for (i = 0; i< 2; i++)
	   ptrBeadArrayOld[i] = (double *)malloc(3 * sizeof(double));
	
	ptrBeadArrayOld[0][0] = 7.0;
	ptrBeadArrayOld[0][1] = 7.0;
	ptrBeadArrayOld[0][2] = 7.0;

        double **oldPtr = *ptrBeadArray;
        
        free_2d(oldPtr, 2,3 );  // you don't know the dimensions here
                
	*ptrBeadArray = ptrBeadArrayOld;   // need to dereference
}


void free_2d(double **d, int nx, int ny)
{
	int x;
	for (x = 0; x < nx; x++) 
{
		free(d[x]);
}
	free(d);
}


int main(void)
{
	int i;
	double **ptrBeadArray = NULL;
	ptrBeadArray = (double **)malloc(2  * sizeof(double *));
	for (i = 0; i< 2; i++)
	   ptrBeadArray[i] = (double *)malloc(3 * sizeof(double));
	
	ptrBeadArray[0][0] = 1.0;
	ptrBeadArray[0][1] = 2.0;
	ptrBeadArray[0][2] = 3.0;
        
        printf("%f\n",ptrBeadArray[0][0]);
        printf("%f\n",ptrBeadArray[0][1]);
        printf("%f\n",ptrBeadArray[0][2]);
	
        MC(&ptrBeadArray);
	
        printf("%f\n",ptrBeadArray[0][0]);
        printf("%f\n",ptrBeadArray[0][1]);
        printf("%f\n",ptrBeadArray[0][2]);
	
	free_2d(ptrBeadArray, 2, 3);
	
	return(0);
}

Kurt

Thanks for that, but does the dereference copy the values over, in otherwords is there any copying of the elements?

Ok thanks for that....

I have now done the re-pointing which has saved sometime. however I have some fixed arrays which are passed in the following way:

Code:

int (*ptrCellIndex)[Xsections][Ysections][Zsections][MaxBeadsinCell], int (*ptrCellIndexCount)[Xsections][Ysections][Zsections]

I then have some static defined variables in the function. I wish to essentially copy one over to the other.

Code:

int CellIndexVolTest[Xsections][Ysections][Zsections][MaxBeadsinCell];
int CellIndexEndVolTest[Xsections][Ysections][Zsections];

What do you suggest I do for this? I need a faster way than just copying elements. The pointer route is'nt possible right? or is it?

Thanks