10-25-2012
Quote:
Originally Posted by
Corona688
free() never returns it to the system -- it just puts it in a list so malloc() knows what to recycle next time.
In the open source world, that hasn't been true for about 10 years. Linux (glibc), OpenBSD, NetBSD, and FreeBSD all return memory to the system under certain circumstances (such as free()ing a massive chunk).
I have no idea how the proprietary libcs behave.
The second half of this post about the exact same topic contains excerpts from a couple of malloc/free implementations, with links to their sources:
https://www.unix.com/302717047-post9.html
Regards,
Alister
This User Gave Thanks to alister For This Post:
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CFREE(3) Linux Programmer's Manual CFREE(3)
NAME
cfree - free allocated memory
SYNOPSIS
#include <stdlib.h>
/* In SunOS 4 */
int cfree(void *ptr);
/* In glibc or FreeBSD libcompat */
void cfree(void *ptr);
/* In SCO OpenServer */
void cfree(char *ptr, unsigned num, unsigned size);
/* In Solaris watchmalloc.so.1 */
void cfree(void *ptr, size_t nelem, size_t elsize);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
cfree(): _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
This function should never be used. Use free(3) instead.
1-arg cfree
In glibc, the function cfree() is a synonym for free(3), "added for compatibility with SunOS".
Other systems have other functions with this name. The declaration is sometimes in <stdlib.h> and sometimes in <malloc.h>.
3-arg cfree
Some SCO and Solaris versions have malloc libraries with a 3-argument cfree(), apparently as an analog to calloc(3).
If you need it while porting something, add
#define cfree(p, n, s) free((p))
to your file.
A frequently asked question is "Can I use free(3) to free memory allocated with calloc(3), or do I need cfree()?" Answer: use free(3).
An SCO manual writes: "The cfree routine is provided for compliance to the iBCSe2 standard and simply calls free. The num and size argu-
ments to cfree are not used."
RETURN VALUE
The SunOS version of cfree() (which is a synonym for free(3)) returns 1 on success and 0 on failure. In case of error, errno is set to
EINVAL: the value of ptr was not a pointer to a block previously allocated by one of the routines in the malloc(3) family.
CONFORMING TO
The 3-argument version of cfree() as used by SCO conforms to the iBCSe2 standard: Intel386 Binary Compatibility Specification, Edition 2.
SEE ALSO
malloc(3)
COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2007-07-26 CFREE(3)