1MALLOC(3)                  Library Functions Manual                  MALLOC(3)
2
3
4

NAME

6       malloc, free, realloc, calloc - main memory allocator
7

SYNOPSIS

9       char *malloc(size)
10       unsigned size;
11
12       free(ptr)
13       char *ptr;
14
15       char *realloc(ptr, size)
16       char *ptr;
17       unsigned size;
18
19       char *calloc(nelem, elsize)
20       unsigned nelem, elsize;
21

DESCRIPTION

23       Malloc  and  free  provide  a  simple general-purpose memory allocation
24       package.  Malloc returns a pointer to a block of at  least  size  bytes
25       beginning on a word boundary.
26
27       The  argument  to  free is a pointer to a block previously allocated by
28       malloc; this space is made available for further  allocation,  but  its
29       contents are left undisturbed.
30
31       Needless  to  say,  grave disorder will result if the space assigned by
32       malloc is overrun or if some random number is handed to free.
33
34       Malloc allocates the first big enough contiguous reach  of  free  space
35       found in a circular search from the last block allocated or freed, coa‐
36       lescing adjacent free blocks  as  it  searches.   It  calls  sbrk  (see
37       break(2))  to get more memory from the system when there is no suitable
38       space already free.
39
40       Realloc changes the size of the block pointed to by ptr to  size  bytes
41       and returns a pointer to the (possibly moved) block.  The contents will
42       be unchanged up to the lesser of the new and old sizes.
43
44       Realloc also works if ptr points to a block freed since the  last  call
45       of  malloc, realloc or calloc; thus sequences of free, malloc and real‐
46       loc can exploit the search strategy of malloc to do storage compaction.
47
48       Calloc allocates space for an array of nelem elements of  size  elsize.
49       The space is initialized to zeros.
50
51       Each  of  the  allocation  routines returns a pointer to space suitably
52       aligned (after possible pointer coercion) for storage of  any  type  of
53       object.
54

DIAGNOSTICS

56       Malloc,  realloc  and  calloc  return a null pointer (0) if there is no
57       available memory or if the arena has been detectably corrupted by stor‐
58       ing  outside  the bounds of a block.  Malloc may be recompiled to check
59       the arena very stringently on every transaction; see the source code.
60

BUGS

62       When realloc returns 0, the block pointed to by ptr may be destroyed.
63
64
65
66                                                                     MALLOC(3)