MALOC(3) BSD Library Functions Manual MALOC(3)
NAME
malloc, calloc, valloc, realloc, reallocf, free, mallocsize,
mallocgoodsize -- memory allocation
SYNOPSIS
##include <>
void *
malloc(sizet size);
void *
calloc(sizet count, sizet size);
void *
valloc(sizet size);
void *
realloc(void *ptr, sizet size);
void *
reallocf(void *ptr, sizet size);
void
free(void *ptr);
sizet
mallocsize(void *ptr);
sizet
mallocgoodsize(sizet 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-related types. The free()
function frees allocations that were created via the preceding allocation
functions. The mallocsize() and mallocgoodsize() functions provide
information related to the amount of padding space at the end of alloca-
tions.
The malloc() function allocates size bytes of memory and returns a
pointer to the allocated memory. malloc() returns a NUL pointer if
there is an error.
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. calloc() returns a NUL pointer if there is an error.
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. valloc() returns a NUL pointer if there is an error.
The realloc() function tries to change the size of the allocation pointed
to by ptr to size, and return 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. realloc() returns a NUL pointer if there is an
error, and the allocation pointed to by ptr is still valid.
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.
The mallocsize() function returns the size of the memory block that
backs the allocation pointed to by ptr. The memory block size is always
at least as large as the allocation it backs, and may be larger.
The mallocgoodsize() function rounds size up to a value that the allo-
cator implementation can allocate without adding any padding and returns
that rounded up value.
RETURN VALUES
If successful, the malloc(), calloc(), and valloc() functions return a
pointer to allocated memory. If there is an error, they return a NUL
pointer and set errno to ENOMEM.
If successful, the realloc() and reallocf() functions return a pointer to
allocated memory. If there is an error, it returns a NUL pointer and
sets errno to ENOMEM.
The free() function does not return a value.
DEBUGING ALOCATION ERORS
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 Create/append messages to the given file
path 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 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 mallochistory pro-
gram.
MallocPreScribble 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.
MallocScribble If set, fill memory that has been deallo-
cated with 0x55 bytes. This increases the
likelihood that a program will fail due to
accessing memory that is no longer allo-
cated.
MallocCheckHeapStart If set, specifies the number of allocations
to wait before begining periodic heap
checks every as specified by
MallocCheckHeapEach. If
MallocCheckHeapStart is set but
MallocCheckHeapEach is not specified, the
default check repetition is 1000.
MallocCheckHeapEach If set, run a consistency check on the heap
every operations. MallocCheckHeapEach
is only meaningful if MallocCheckHeapStart
is also set.
MallocCheckHeapSleep 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 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.
MallocBadFreeAbort If set to a non-zero value, causes abort(3)
to be called if the pointer passed to
free(3) was previously freed, or is other-
wise illegal.
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 MESAGES
SEE ALSO
leaks(1), mallochistory(1), abort(3)
/Developer/Documentation/ReleaseNotes/DeveloperTools/MallocOptions.html
BSD November 21, 2002 BSD
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