MALLOC(3) BSD Library Functions Manual MALLOC(3)
calloc, free, malloc, realloc, reallocf, valloc -- memory allocation
calloc(size_t count, size_t size);
realloc(void *ptr, size_t size);
reallocf(void *ptr, size_t size);
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
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
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 guarantee 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
The free() function deallocates the memory allocation pointed to by ptr. If ptr is a NULL pointer, no operation is performed.
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 realloca-
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
environment variables. The recognized environment variables and their meanings are documented below.
The following environment variables change the behavior of the allocation-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 environment variable is set.
MallocDoNotProtectPostlude If set, do not add a guard page after large blocks, even if the MallocGuardEdges environment 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 struc-
tures, instead of an on-disk log.
MallocStackLoggingNoCompact If set, record all stacks in a manner that is compatible with the malloc_history program.
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 likelihood that a program mak-
ing 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 mem-
ory 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 speci-
fied 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 corruption is detected. The default is 100 seconds. Setting this to zero means not to sleep at all. Set-
ting this to a negative number means to sleep (for the positive number 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. MallocCorruptionAbort is always set on 64-bit processes.
MallocHelp If set, print a list of environment variables that are paid heed to by the allocation-related functions, along
with short descriptions. The list should correspond to this documentation.
leaks(1), malloc_history(1), abort(3), malloc_size(3), malloc_zone_malloc(3), posix_memalign(3), libgmalloc(3)
Aug 13, 2008 BSD