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Annotation of 43BSDReno/lib/libc/stdlib/malloc.3, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)malloc.3    6.4 (Berkeley) 6/9/89
        !             6: .\"
        !             7: .TH MALLOC 3  "June 9, 1989"
        !             8: .UC 4
        !             9: .SH NAME
        !            10: malloc, free, realloc, calloc, alloca \- memory allocator
        !            11: .SH SYNOPSIS
        !            12: .nf
        !            13: .B char *malloc(size)
        !            14: .B unsigned size;
        !            15: .PP
        !            16: .B free(ptr)
        !            17: .B char *ptr;
        !            18: .PP
        !            19: .B char *realloc(ptr, size)
        !            20: .B char *ptr;
        !            21: .B unsigned size;
        !            22: .PP
        !            23: .B char *calloc(nelem, elsize)
        !            24: .B unsigned nelem, elsize;
        !            25: .PP
        !            26: .B char *alloca(size)
        !            27: .B int size;
        !            28: .fi
        !            29: .SH DESCRIPTION
        !            30: .I Malloc
        !            31: and
        !            32: .I free
        !            33: provide a general-purpose memory allocation package.
        !            34: .I Malloc
        !            35: returns a pointer to a block of at least
        !            36: .I size
        !            37: bytes beginning on a word boundary.
        !            38: .PP
        !            39: The argument to
        !            40: .I free
        !            41: is a pointer to a block previously allocated by
        !            42: .IR malloc ;
        !            43: this space is made available for further allocation,
        !            44: but its contents are left undisturbed.
        !            45: .PP
        !            46: Needless to say, grave disorder will result if the space assigned by
        !            47: .I malloc
        !            48: is overrun or if some random number is handed to
        !            49: .IR free .
        !            50: .PP
        !            51: .I Malloc
        !            52: maintains multiple lists of free blocks according to size,
        !            53: allocating space from the appropriate list.
        !            54: It calls
        !            55: .I sbrk
        !            56: (see
        !            57: .IR brk (2))
        !            58: to get more memory from the system when there is no
        !            59: suitable space already free.
        !            60: .PP
        !            61: .I Realloc
        !            62: changes the size of the block pointed to by
        !            63: .I ptr
        !            64: to
        !            65: .I size
        !            66: bytes and returns a pointer to the (possibly moved) block.
        !            67: The contents will be unchanged up to the lesser of the new and old sizes.
        !            68: If
        !            69: .I ptr
        !            70: is null,
        !            71: .I realloc
        !            72: simply returns the value of
        !            73: .I malloc
        !            74: called with an argument of
        !            75: .IR size .
        !            76: .PP
        !            77: In order to be compatible with older versions,
        !            78: .I realloc
        !            79: also works if
        !            80: .I ptr
        !            81: points to a block freed since the last call of
        !            82: .I malloc, realloc
        !            83: or
        !            84: .IR calloc ;
        !            85: sequences of
        !            86: .I free, malloc
        !            87: and
        !            88: .I realloc
        !            89: were previously used to attempt storage compaction.
        !            90: This procedure is no longer recommended.
        !            91: .PP
        !            92: .I Calloc
        !            93: allocates space for an array of
        !            94: .I nelem
        !            95: elements of size
        !            96: .I elsize.
        !            97: The space is initialized to zeros.
        !            98: .PP
        !            99: .I Alloca
        !           100: allocates 
        !           101: .I size
        !           102: bytes of space in the stack frame of the caller.
        !           103: This temporary space is automatically freed on
        !           104: return.
        !           105: .PP
        !           106: Each of the allocation routines returns a pointer
        !           107: to space suitably aligned (after possible pointer coercion)
        !           108: for storage of any type of object.
        !           109: If the space is of
        !           110: .I pagesize
        !           111: or larger, the memory returned will be page-aligned.
        !           112: .SH SEE ALSO
        !           113: brk(2),
        !           114: pagesize(2)
        !           115: .SH DIAGNOSTICS
        !           116: .I Malloc, realloc
        !           117: and
        !           118: .I calloc
        !           119: return a null pointer (0) if there is no available memory or if the arena
        !           120: has been detectably corrupted by storing outside the bounds of a block.
        !           121: .I Malloc
        !           122: may be recompiled to check the arena very stringently on every transaction;
        !           123: those sites with a source code license may check the source code to see
        !           124: how this can be done.
        !           125: .SH BUGS
        !           126: When
        !           127: .I realloc
        !           128: returns 0, the block pointed to by
        !           129: .I ptr
        !           130: may be destroyed.
        !           131: .PP
        !           132: The current implementation of
        !           133: .I malloc
        !           134: does not always fail gracefully when system
        !           135: memory limits are approached.
        !           136: It may fail to allocate memory when larger free blocks could be broken
        !           137: up, or when limits are exceeded because the size is rounded up.
        !           138: It is optimized for sizes that are powers of two.
        !           139: .PP
        !           140: .I Alloca
        !           141: is machine dependent; its use is discouraged.

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