Dynamic allocation of multi dimensional array

[gianluca]

Hy list,

I've to declare a 3D matrix in C . I tried with that code:

double ***mat;

mat=(double***)G_malloc(ndimension*(sizeof(double));

but the program send me a run time error.

could anybody help me?
thanks
gianluca

 

[Ben Bacarisse]

I've to declare a 3D matrix in C . I tried with that code:

double ***mat;

mat=(double***)G_malloc(ndimension*(sizeof(double));

The cast is either hiding a type error (if G_malloc does not return the
right sort of pointer) or it is pointless. Much better to leave it out.

but the program send me a run time error.

could anybody help me?

Not without seeing the program, or a shorter version that just shows
the error you are getting.

 

[Bartc]

Hy list,

I've to declare a 3D matrix in C . I tried with that code:

double ***mat;

mat=(double***)G_malloc(ndimension*(sizeof(double));

but the program send me a run time error.

could anybody help me?

I tried this:

#include "stdio.h"
#include "stdlib.h"

#define xdim 5
#define ydim 10
#define zdim 15

int main(void) {
double ***mat;
int i,j,k,n;

mat=malloc(sizeof(double*)*xdim);

for (i=0; i<xdim; ++i) {
mat=malloc(sizeof(double*)*ydim);
for (j=0; j<ydim; ++j)
mat[j]=malloc(sizeof(double)*zdim);
}

n=0;
for (i=0; i<xdim; ++i)
for (j=0; j<ydim; ++j)
for (k=0; k<zdim; ++k)
mat[j][k] = ++n;

for (i=0; i<xdim; ++i)
for (j=0; j<ydim; ++j)
for (k=0; k<zdim; ++k)
printf("mat[%d][%d][%d] = %f\n",i,j,k,mat[j][k]);

}

In practice, malloc returns should be checked.

C's multi-dimensional dynamic arrays I think need to be allocated as Iliffe
vectors. But once
done then they are indexed as normal.

 

[vippstar]

One way of creating a multi-dimensional array is to allocate a double ***for
the z axis, with as many entries as you have in the y axis, then allocate
double **s for the yaxes, then double *s for the x axes.

The other way is to create a single dimensional array of xsize * ysize *
zsize * sizeof(double). Then you have to do the index calcuations by hand.

Personally I tend to find the second way easier. However neither is ideal.

There's pros and cons with both. For example, in the second, if you
have columns/rows, and you want to change the rows from 10 to 5, you
can't simply realloc. (whereas with the first you just loop over the
rows and realloc)
It's best to either use some lib or some other programming language.

 

[Barry Schwarz]

#include "stdio.h"
#include "stdlib.h"

#define xdim 5
#define ydim 10
#define zdim 15

int main(void) {
double ***mat;
int i,j,k,n;

mat=malloc(sizeof(double*)*xdim);

This need not allocate the correct amount of space. The object(s) mat
points to must be double**.

 

[Barry Schwarz]

Hy list,

I've to declare a 3D matrix in C . I tried with that code:

double ***mat;

mat=(double***)G_malloc(ndimension*(sizeof(double));

but the program send me a run time error.

could anybody help me?

See question 6.16 of the C faq at www.c-faq.com.

 

[Barry Schwarz]

There's pros and cons with both. For example, in the second, if you
have columns/rows, and you want to change the rows from 10 to 5, you
can't simply realloc. (whereas with the first you just loop over the
rows and realloc)
It's best to either use some lib or some other programming language.

You know of a C library that makes dynamic arrays easier?

You know of a language that makes allocating dynamic arrays easier?

 

[Ian Collins]

You know of a language that makes allocating dynamic arrays easier?

In C++ it would be easier (both in construction and adding/removing
arrays) with vectors of vectors.

 

[vippstar]

You know of a C library that makes dynamic arrays easier?
No

You know of a language that makes allocating dynamic arrays easier?

Yes