malloc(3C)                                             malloc(3C)



NAME
     malloc, free, realloc, calloc, cfree - provide a 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;

     void cfree(ptr,nelem,elsize)
     char *ptr;
     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 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 occur if the space assigned by malloc is
     overrun or if some random number is handed to free.

     malloc allocates the first contiguous reach of free space of
     sufficient size found in a circular search from the last
     block allocated or freed; it coalesces 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 are unchanged up to the lesser of the
     new and old sizes.  If no free block of size bytes is
     available in the storage arena, realloc asks malloc to
     enlarge the arena by size bytes and then moves 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



January 1992                                                    1

malloc(3C)                                             malloc(3C)



     free, malloc, and realloc can exploit 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.

     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.

STATUS MESSAGES AND VALUES
     The malloc, realloc, and calloc programs return a NULL
     pointer if there is no available memory or if the arena is
     detected to have been corrupted by storing outside the
     bounds of a block.  When this happens the block pointed to
     by ptr may be destroyed.

NOTES
     Search time increases when many objects have been allocated;
     that is, if a program allocates space but never frees it,
     each successive allocation takes longer.

SEE ALSO
     brk(2), malloc(3X)




























2                                                    January 1992