malloc(3C) malloc(3C)
NAME
malloc, free, realloc, calloc, alloca - 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;
SYNOPSIS (4.2BSD)
char *alloca (size)
int size;
DESCRIPTION
malloc and free provide a simple general-purpose memory
allocation package. malloc returns a pointer to a block of
at least size bytes beginning on a word boundary.
The argument to free is a pointer to a block previously
allocated by malloc; this space is made available for
further allocation, but its contents are left undisturbed.
Needless to say, grave disorder will result if the space
assigned by malloc is overrun or if some random number is
handed to free.
malloc maintains multiple lists of free blocks according to
size, allocating space from the appropriate list. 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 ptr is NULL, then malloc will be
called to return a pointer to a block of at least size bytes
beginning on a word boundary.
In order to be compatible with older versions, realloc also
works if ptr points to a block freed since the last call of
malloc, realloc or calloc; sequences of free, malloc and
realloc were previously used to attempt storage compaction.
This procedure is no longer recommended.
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malloc(3C) malloc(3C)
Calloc allocates space for an array of nelem elements of
size elsize. The space is initialized to zeros.
Alloca allocates size bytes of space in the stack frame of
the caller. This temporary space is automatically freed on
return.
Each of the allocation routines returns a pointer to space
suitably aligned (after possible pointer coercion) for
storage of any type of object.
DIAGNOSTICS
Malloc, realloc and calloc return a null pointer (0) if
there is no available memory or if the area has been detect-
ably corrupted by storing outside the bounds of a block.
malloc may be recompiled to check the area very stringently
on every transaction; those sites with a source code license
may check the source code to see how this can be done.
BUGS
When realloc returns 0, the block pointed to by ptr may be
destroyed.
Alloca is machine dependent; its use is discouraged.
Page 2 CX/UX Programmer's Reference Manual