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 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 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 environment variables. The recognized environment variables and their meanings are documented below.

ENVIRONMENT
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
    If set, record all stacks, so that tools like leaks can be used.

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 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 corruption 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 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.

DIAGNOSTIC MESSAGES

SEE ALSO
leaks(1), malloc_history(1), abort(3), malloc_size(3), malloc_zone_malloc(3), posix_memalign(3), libgmalloc(3)