ID Number: Q32998
4.00 5.00 5.10 6.00 6.00a 6.00ax 7.00 | 5.10 6.00 6.00a
MS-DOS | OS/2
Summary:
When trying to allocate memory with malloc() and calloc(), the request
for memory is truncated if it exceeds 64K.
The maximum number of bytes that can be allocated by malloc() is less
than 64K because the allocation routines consume a certain number of
bytes to track memory allocation within the segment. The maximum
number of bytes you can allocate using malloc() or calloc is
approximately 65516 with C 5.1 and earlier and 65512 with C 6.0 and
later.
Requests for more than 65512 bytes and less than 64K results in malloc
returning NULL. Requests for more than 64K may return a pointer;
however, it will be a pointer to a block of a size other than that
requested because the parameter passed to malloc() is an unsigned
integer. This integer has a maximum value of 64K; passing a number
greater than this value results in undefined behavior. If malloc() is
passed a parameter greater than 64K, the compiler will issue a
data-conversion warning, which should be heeded.
If you require more than about 65512 bytes for a single allocation,
you should use halloc().
More Information:
The following program demonstrates the behavior described above:
Sample Code
-----------
/* Compile options needed: none
*/
#include <stdio.h>
#include <malloc.h>
int *intarray;
main()
{
intarray= (int *)malloc(32768*sizeof(int));
if (intarray == NULL)
printf("not enough memory, no allocation");
else
printf("memory allocated");
intarray= (int *)malloc(32767*sizeof(int));
if (intarray == NULL)
printf("not enough memory, no allocation");
else
printf("memory allocated");
}
Additional reference words: 5.00 5.10 6.00 6.00a 6.00ax 7.00