Syntax

#include <stdlib.h>  /* also in <malloc.h> */
size_t _msize(void *ptr)

• msize determines the number of bytes that were allocated to the pointer argument ptr. The ptr must have been returned from one of the run-time memory allocation functions (_ucalloc, malloc, _trealloc, and so on).

  You cannot pass the argument of an object that has been freed.

• msize returns the number of bytes allocated. If the argument is not a valid pointer returned from a memory allocation function, the return value is undefined. If NULL is passed, _msize returns 0.

This example displays the size of an allocated object from malloc.

#include <stdlib.h>
#include <stdio.h>

int main(void)
{
   char *ptr;

   if (NULL == (ptr = malloc(10))) {
      puts("Could not allocate memory block.");
      exit(EXIT_FAILURE);
   }
   memset(ptr, 'x', 5);
   printf("The size of the allocated object is %u.\n",_msize(ptr));
   return 0;

   /****************************************************************************
      The output should be similar to :

      The size of the allocated object is 10.
   ****************************************************************************/
}

• calloc
  
• malloc
  
• realloc

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