MATLAB Application Program Interface Reference

Get the number of dimensions

#include "matrix.h"
int mxGetNumberOfDimensions(const mxArray *array_ptr);

Arguments

array_ptr

Pointer to an mxArray.

Returns

The number of dimensions in the specified mxArray. The returned value is always 2 or greater.

Description

Use mxGetNumberOfDimensions to determine how many dimensions are in the specified array. To determine how many elements are in each dimension, call mxGetSize.

Examples

Consider a MEX-file named CountDim that calls mxGetNumberOfDimensions to determine how many dimensions are in the first input argument.

void
mexFunction(int nlhs,mxArray *plhs[],int nrhs,const mxArray 
*prhs[])
{
 int  number_of_dimensions; 
 int *dims;
 int  c;

  /* Look at the number of dimensions in the input mxArray. */
    number_of_dimensions = mxGetNumberOfDimensions(prhs[0]); 

  /* Create a dimensions array having the same number of dimensions 
as the input mxArray.  Arbitrarily make the length of each 
dimension be 2. */ 
 
    dims = mxCalloc(number_of_dimensions, sizeof(int));
    for (c=0; c<number_of_dimensions; c++)
       dims[c]=2;

  /* Create an mxArray of signed 16-bit integers. */ 
    mxCreateNumericArray(number_of_dimensions, dims, 
mxINT16_CLASS, mxREAL);
   ...
}

In MATLAB, create a three-dimensional mxArray named td. Then pass td as an argument to CountDim

>> td = rand(6, 4, 2);
>> CountDim(td)

Since td is a 3-dimensional mxArray, CountDim creates a 2-by-2-by-2 mxArray. If td had been a 4-dimensional mxArray, CountDim would have created a 2-by-2-by-2-by-2.

For an additional example, see mxGetNumberOfDimensions.c in the mx subdirectory of the examples directory.