MALLOC(3C)              COMMAND REFERENCE              MALLOC(3C)



NAME
     malloc, free, realloc, calloc - main memory allocator

SYNOPSIS
     char *malloc(size)
     unsigned size;

     free(ptr)
     char *ptr;

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

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

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, serious disorder will result 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.

     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 force the search strategy of
     malloc to do storage compaction.

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

     Each of the allocation routines returns a pointer to space
     suitably aligned (after possible pointer coercion) for



Printed 3/13/89                                                 1

MALLOC(3C)              COMMAND REFERENCE              MALLOC(3C)



     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 arena has been
     detectably corrupted by storing outside the bounds of a
     block.

CAVEATS
     When realloc returns 0, the block pointed to by ptr may be
     destroyed.

SEE ALSO
     brk(2).









































Printed 3/13/89                                                 2

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