Re: How does free() know how many bytes to free???

MAx wrote:
Hi,
A call to free() is used to de allocate memory which has been
allocated by a malloc()
or a calloc() call.
How does free() know how many bytes to deallocate?

The size is stored in bytes just before the useful area. Note that additional bits are used for other purposes.

Here's a small (32 bit!) program to show:

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

void
all(size_t s)
{
unsigned char *ucp;
int i;

ucp = malloc(s);
printf("%#x:", s);
for (i = 0; i < 8; i++)
printf(" %02x", ucp[i-8]);
printf("\n");
}

int
main(int argc, char *argv)
{
all(0x1234);
all(0x12340);
all(0x123400);
}

--
These are my personal views and not those of Fujitsu Siemens Computers!
Josef Möllers (Pinguinpfleger bei FSC)
If failure had no penalty success would not be a prize (T. Pratchett)
Company Details: http://www.fujitsu-siemens.com/imprint.html

.

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