MATLAB Application Program Interface Reference

Set new real data for an mxArray

#include "matrix.h"
void mxSetPr(mxArray *array_ptr, double *pr);

Arguments

array_ptr

Pointer to a full (nonsparse) mxArray.

Pointer to the first element of an array. Each element in the array contains the real component of a value. The array must be in dynamic memory; call mxCalloc to allocate this dynamic memory. If pr points to static memory, then memory leaks and other memory errors may result.

Description

Use mxSetPr to set the real data of the specified mxArray.

All mxCreate calls allocate heap space to hold real data. Therefore, you do not ordinarily use mxSetPr to initialize the real elements of a freshly-created mxArray. Rather, you typically call mxSetPr to replace the initial real values with new ones.

Examples

Create a populated 2-by-3 real-only mxArray. Then, change its data.

mxArray  *array_ptr;
  double    start_pr[6] = {3.2, 4.6, 5.1, 6.8, 7.3, 8.1};
  double   *start_of_real_data, *next_data, *pr;
  int       c;

 /* Create a 2-by-3 real-only array of doubles. */ 
   array_ptr = mxCreateDoubleMatrix(2, 3, mxREAL);
   pr = mxGetPr(array_ptr);
   memcpy((void *)pr,(const void *)start_pr,6*sizeof(double));
   mxSetName(array_ptr, "Apricot");

   ...

 /* Redo "Apricot", changing its size and its real data. */ 
 
 /* First, deallocate the old pr data. */
   mxFree(mxGetPr(array_ptr));

 /* Next, change Apricot's dimensions to 2-by-4. */
   mxSetN(array_ptr, 4);
 
 /* Next, allocate memory to hold 8 real elements. */ 
   start_of_real_data = 
      (double *)mxCalloc(8, mxGetElementSize(array_ptr));

 /* Place 8 values in the newly allocated memory. */
   next_data = start_of_real_data;
   for (c=12; c<20; c++) 
      *next_data++ = sqrt(c);

 /* Associate the new data with the real data of Apricots. */ 
   mxSetPr(array_ptr, start_of_real_data);

Apricot initially contains

3.2000    5.1000    7.3000
4.6000    6.8000    8.1000

After calling mxSetPr, Apricot contains

3.4641    3.7417    4.0000
3.6056    3.8730    4.1231

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