NAME

malloc, free, realloc, calloc, cfree, malloc_check − main memory allocator

SYNOPSIS

char ∗malloc (size)
unsigned size;

void free (ptr)
char ∗ptr;

char ∗realloc (ptr, size)
char ∗ptr;
unsigned size;

char ∗calloc (nelem, elsize)
unsigned nelem, elsize;

cfree (ptr, nelem, elsize)
char *ptr;
unsigned nelem, elsize;

malloc_check (ptr)
char *ptr;

DESCRIPTION

Malloc and free provide a general-purpose memory allocation package.  Malloc returns a pointer to a block of at least size bytes suitably aligned for any use. 

The argument to free is a pointer to a block previously allocated by malloc; after free is performed this space is made available for further allocation, but its contents are left undisturbed. 

Undefined results will occur if the space assigned by malloc is overrun or if some random number is handed to free.

Malloc allocates the first big enough contiguous reach of free space found in a circular search from the last block allocated or freed, coalescing adjacent free blocks as it searches.  It calls sbrk (see brk(2)) to get more memory from the system when there is no suitable space already free.

Realloc changes the size of the block pointed to by ptr to size bytes and returns a pointer to the (possibly moved) block.  The contents will be unchanged up to the lesser of the new and old sizes.  If no free block of size bytes is available in the storage arena, then realloc will ask malloc to enlarge the arena by size bytes and will then move the data to the new space. 

Realloc also works if ptr points to a block freed since the last call of malloc, realloc, or calloc; thus sequences of free, malloc and realloc can exploit the search strategy of malloc to do storage compaction.  Note that while previous versions of malloc tended to fragment the storage arena, the current version attempts to keep free space compact.  Therefore using realloc on free space is deprecated. 

Calloc allocates space for an array of nelem elements of size elsize. The space is initialized to zeros.

The arguments to cfree are the pointer to a block previously allocated by calloc plus the parameters to calloc.

Each of the allocation routines returns a pointer to space suitably aligned (after possible pointer coercion) for storage of any type of object. 

As an aid to debugging, the source for these routines is provided in /usr/people/gifts/malloc/malloc.c.  When compiled with the preprocessor symbol HEAP_CHECK defined, calls to malloc_check perform a thorough consistency check of the storage arena.  This check is also done on each call to malloc, realloc, and free. If the check detects corruption, it prints a message describing the corruption and terminates execution with abort(3C). Without HEAP_CHECK , no consistency checking is done.  The standard C library version does no checking. 

DIAGNOSTICS

Malloc, realloc and calloc return a NULL pointer if there is no available memory.  When this happens the block pointed to by ptr may be destroyed. 

FILES

/usr/people/gifts/malloc/malloc.csource for allocator

NOTES

Release 3.6 introduced a rewritten version of these functions.  To use the old version, link with /usr/lib/liboldmalloc.a. 

Version 3.6  —  December 20, 1987