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Unix manual page for free. (host=minya system=Darwin)
MALLOC(3) BSD Library Functions Manual MALLOC(3)
NAME
calloc, free, malloc, realloc, reallocf, valloc -- memory allocation
SYNOPSIS
#include <stdlib.h>
void *
calloc(size_t count, size_t size);
void
free(void *ptr);
void *
malloc(size_t size);
void *
realloc(void *ptr, size_t size);
void *
reallocf(void *ptr, size_t size);
void *
valloc(size_t size);
DESCRIPTION
The malloc(), calloc(), valloc(), realloc(), and reallocf() functions
allocate memory. The allocated memory is aligned such that it can be
used for any data type, including AltiVec- and SSE-related types. The
free() function frees allocations that were created via the preceding
allocation functions.
The malloc() function allocates size bytes of memory and returns a
pointer to the allocated memory.
The calloc() function contiguously allocates enough space for count
objects that are size bytes of memory each and returns a pointer to the
allocated memory. The allocated memory is filled with bytes of value
zero.
The valloc() function allocates size bytes of memory and returns a
pointer to the allocated memory. The allocated memory is aligned on a
page boundary.
The realloc() function tries to change the size of the allocation pointed
to by ptr to size, and returns ptr. If there is not enough room to
enlarge the memory allocation pointed to by ptr, realloc() creates a new
allocation, copies as much of the old data pointed to by ptr as will fit
to the new allocation, frees the old allocation, and returns a pointer to
the allocated memory. If ptr is NULL, realloc() is identical to a call
to malloc() for size bytes. If size is zero and ptr is not NULL, a new,
minimum sized object is allocated and the original object is freed. When
extending a region allocated with calloc(3), realloc(3) does not guaran-
tee that the additional memory is also zero-filled.
The reallocf() function is identical to the realloc() function, except
that it will free the passed pointer when the requested memory cannot be
allocated. This is a FreeBSD specific API designed to ease the problems
with traditional coding styles for realloc causing memory leaks in
libraries.
The free() function deallocates the memory allocation pointed to by ptr.
If ptr is a NULL pointer, no operation is performed.
RETURN VALUES
If successful, calloc(), malloc(), realloc(), reallocf(), and valloc()
functions return a pointer to allocated memory. If there is an error,
they return a NULL pointer and set errno to ENOMEM.
For realloc(), the input pointer is still valid if reallocation failed.
For reallocf(), the input pointer will have been freed if reallocation
failed.
The free() function does not return a value.
DEBUGGING ALLOCATION ERRORS
A number of facilities are provided to aid in debugging allocation errors
in applications. These facilities are primarily controlled via environ-
ment variables. The recognized environment variables and their meanings
are documented below.
ENVIRONMENT
The following environment variables change the behavior of the alloca-
tion-related functions.
MallocLogFile <f> Create/append messages to the given file
path <f> instead of writing to the standard
error.
MallocGuardEdges If set, add a guard page before and after
each large block.
MallocDoNotProtectPrelude If set, do not add a guard page before large
blocks, even if the MallocGuardEdges envi-
ronment variable is set.
MallocDoNotProtectPostlude If set, do not add a guard page after large
blocks, even if the MallocGuardEdges envi-
ronment variable is set.
MallocStackLogging The default behavior if this is set is to
record all allocation and deallocation
events to an on-disk log, along with stacks,
so that tools like leaks(1) and
malloc_history(1) can be used.
Set to "vm" to record only allocation of
virtual memory regions allocated by system
calls and mach traps, such as by mmap(1)
Set to "malloc" to record only allocations
via malloc(3) and related interfaces, not
virtual memory regions.
Set to "lite" to record current allocations
only, not history. These are recorded by
in-memory data structures, instead of an on-
disk log.
MallocStackLoggingNoCompact If set, record all stacks in a manner that
is compatible with the malloc_history pro-
gram.
MallocStackLoggingDirectory If set, records stack logs to the directory
specified instead of saving them to the
default location (/tmp).
MallocScribble If set, fill memory that has been allocated
with 0xaa bytes. This increases the likeli-
hood that a program making assumptions about
the contents of freshly allocated memory
will fail. Also if set, fill memory that
has been deallocated with 0x55 bytes. This
increases the likelihood that a program will
fail due to accessing memory that is no
longer allocated.
MallocCheckHeapStart <s> If set, specifies the number of allocations
<s> to wait before begining periodic heap
checks every <n> as specified by
MallocCheckHeapEach. If
MallocCheckHeapStart is set but
MallocCheckHeapEach is not specified, the
default check repetition is 1000.
MallocCheckHeapEach <n> If set, run a consistency check on the heap
every <n> operations. MallocCheckHeapEach
is only meaningful if MallocCheckHeapStart
is also set.
MallocCheckHeapSleep <t> Sets the number of seconds to sleep (waiting
for a debugger to attach) when
MallocCheckHeapStart is set and a heap cor-
ruption is detected. The default is 100
seconds. Setting this to zero means not to
sleep at all. Setting this to a negative
number means to sleep (for the positive num-
ber of seconds) only the very first time a
heap corruption is detected.
MallocCheckHeapAbort <b> When MallocCheckHeapStart is set and this is
set to a non-zero value, causes abort(3) to
be called if a heap corruption is detected,
instead of any sleeping.
MallocErrorAbort If set, causes abort(3) to be called if an
error was encountered in malloc(3) or
free(3) , such as a calling free(3) on a
pointer previously freed.
MallocCorruptionAbort Similar to MallocErrorAbort but will not
abort in out of memory conditions, making it
more useful to catch only those errors which
will cause memory corruption. MallocCorrup-
tionAbort is always set on 64-bit processes.
MallocHelp If set, print a list of environment vari-
ables that are paid heed to by the alloca-
tion-related functions, along with short
descriptions. The list should correspond to
this documentation.
DIAGNOSTIC MESSAGES
SEE ALSO
leaks(1), malloc_history(1), abort(3), malloc_size(3),
malloc_zone_malloc(3), posix_memalign(3), libgmalloc(3)
BSD Aug 13, 2008 BSD