| MATLAB Application Program Interface | Search Help Desk |
| mxGetElementSize | Examples See Also |
Get the number of bytes required to store each data element
#include "matrix.h" int mxGetElementSize(const mxArray *array_ptr);array_ptr
mxArray.
The number of bytes required to store one element of the specified mxArray, if successful. Returns 0 on failure. The primary reason for failure is that array_ptr points to an mxArray having an unrecognized class. If array_ptr points to a cell mxArray or a structure mxArray, then mxGetElementSize returns the size of a pointer (not the size of all the elements in each cell or structure field).
Call mxGetElementSize to determine the number of bytes in each data element of the mxArray. For example, if the mxClassID of an mxArray is mxINT16_CLASS, then the mxArray stores each data element as a 16-bit (2 byte) signed integer. Thus, mxGetElementSize returns 2.
mxGetElementSize is particularly helpful when using a nonMATLAB routine to manipulate data elements. For example, memcpy requires (for its third argument) the size of the elements you intend to copy.
Consider a MEX-file that calls memcpy to make a copy of whatever kind of data gets passed to it. The third argument to memcpy is the number of bytes to copy. In order to determine the number of bytes, you must first call mxGetElementSize.
void
mexFunction(int nlhs,mxArray *plhs[],int nrhs,const mxArray
*prhs[])
{
int bytes_per_element, total_elements;
void *pr, *mycopy;
/* Get the characteristics of the input mxArray. */
bytes_per_element = mxGetElementSize(prhs[0]);
total_elements = mxGetM(prhs[0]) * mxGetN(prhs[0]);
pr = mxGetPr(prhs[0]);
/* Allocate enough heap to hold a copy of the real elements of
the input mxArray. Then copy them. */
mycopy = mxCalloc(total_elements, bytes_per_element);
memcpy(mycopy, pr, bytes_per_element * total_elements);
...
For an additional example, see mxgetelementsize.c in the mx subdirectory of the examples directory.
mxGetM, mxGetN