mxMalloc (MATLAB Application Program Interface)

Allocate dynamic memory using MATLAB's memory manager

#include "matrix.h"
#include <stdlib.h>
void *mxMalloc(size_t n);

Arguments

n
Number of bytes to allocate.

Returns

A pointer to the start of the allocated dynamic memory, if successful. If unsuccessful in a stand-alone (nonMEX-file) application, mxMalloc returns NULL. If unsuccessful in a MEX-file, the MEX-file terminates and control returns to the MATLAB prompt.

mxMalloc is unsuccessful when there is insufficient free heap space.

Description

MATLAB applications should always call mxMalloc rather than malloc to allocate memory. Note that mxMalloc works differently in MEX-files than in stand-alone MATLAB applications.

In MEX-files, mxMalloc automatically

Allocates enough contiguous heap space to hold n bytes.
Registers the returned heap space with the MATLAB memory management facility.

The MATLAB memory management facility maintains a list of all memory allocated by mxMalloc. The MATLAB memory management facility automatically frees (deallocates) all of a MEX-file's parcels when control returns to the MATLAB prompt.

In stand-alone MATLAB applications, mxMalloc defaults to calling the ANSI C malloc function. If this default behavior is unacceptable, you can write your own memory allocation routine, and then register this routine with mxSetAllocFcns. Then, whenever mxMalloc is called, mxMalloc calls your memory allocation routine instead of malloc.

By default, in a MEX-file, mxMalloc generates nonpersistent mxMalloc data. In other words, the memory management facility automatically deallocates the memory as soon as the MEX-file ends. If you want the memory to persist after the MEX-file completes, call mexMakeMemoryPersistent after calling mxMalloc. If you write a MEX-file with persistent memory, be sure to register a mexAtExit function to free allocated memory in the event your MEX-file is cleared.

When you finish using the memory allocated by mxMalloc, call mxFree. mxFree deallocates the memory.

Examples

This example uses mxMalloc to allocate enough heap space to hold a string.

void
mexFunction(int nlhs,mxArray *plhs[],int nrhs,const mxArray 
*prhs[])
{
 char *buf;
 int   buflen;
 int   status;

   if (mxIsString(prhs[0]))  {
   /* Find out how long the input string array is. */
     buflen = mxGetN(prhs[0])+1;
   /* Allocate enough memory to hold the converted string. */ 
     buf = mxMalloc(buflen);
   /* Copy the string data into buf. */ 
     status = mxGetString(prhs[0], buf, buflen); 
   /* Manipulate the string.*/
        ...

   /* When finished using the string, deallocate it. */
     mxFree(buf);
   }
   else
     mexErrMsgTxt("Input argument must be a string.");

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