Programming

Can anyone tell me why this section of code causes a segmentation fault when 'deallocate' is called?. Although it works when n>=number.
This code segment is intended to be used in a program in which the tensor is very large, (5x512x512) or greater.

i tryed to compile this using gcc version 2.95.4


#include <stdio.h>
#include <malloc.h>

int number = 8;
double ***tensor;

void allocate()
{
int i,j;
int n = 3;
tensor = (double***)malloc(sizeof(double**)*n);
for(j=0;j<number;j++)
{
tensor[j] = (double**)malloc(sizeof(double*)*number);
for(i=0;i<number;i++)
tensor[j][i] = (double*)malloc(sizeof(double)*number);
}
}

void deallocate()
{
int i,j;
for(i=0;i<number;i++)
{
for(j=0;j<number;j++)
free(tensor[i][j]);
free(tensor[i]);
}
free(tensor);
}

int main(void)
{
allocate();
deallocate();
return 0;
}

See this thread.

I think I have got the answer.

The deallocate function is right. There is a problem in the allocate function.

When you allocate memory to 'tensor', you use:
tensor = (double***)malloc(sizeof(double**)*n);
that is to say, you just can access tensor through 0 to n. If you want to access tensor[i] which i > n , then a problem will arise.
That's the reason why it works when number < n and doesn't work when number > n.

By the way, I think there is a simple way to allocate a block of memory to the big array such as 'tensor'.
allocate:
tensor = (double***)malloc(sizeof(double)*number*number*n);
deallocate:
free(tensor);

Hope it be helpful.