[GRASS-user] GRASS Dynamic allocation of multi dimensional array

[Glynn Clements]

gianluca massei wrote:

> could anybody help me to declare a 3D matrix in C GRASS module. I've to 
> load several raster map with same location but I've an error in run time 
> if I declare with G_malloc/G_calloc like that:
> double ***mat;
> 
> mat=(double***)G_malloc(ndimension*(sizeof(double));

To implement variable-size multi-dimensional arrays in C, you have two
options:

1. Allocate a single contiguous block and calculate the indices
yourself, e.g.:

	double *data = G_malloc(width * height * depth * sizeof(double));

	#define DATA(x,y,z) (data[((z) * height + (y)) * width + (x)])

	...

	/* read element */
	v = DATA(x,y,z);

	/* write element */
	DATA(x,y,z) = v;

2. Create arrays of pointers:

	int i, j;
	double ***data = G_malloc(depth * sizeof(double **));
	for (j = 0; j < depth; j++)
	{
		data[j] = G_malloc(height * sizeof(double *));
		for (i = 0; i < height; i++)
			data[j][i] = G_malloc(width * sizeof(double));
	}

	...

	/* read element */
	v = data[z][y][x];

	/* write element */
	data[z][y][x] = v;

-- 
Glynn Clements <glynn at gclements.plus.com>