malloc(3X)                     DG/UX R4.11MU05                    malloc(3X)


NAME
       malloc, free, realloc, calloc, mallopt, mallinfo - memory allocator

SYNOPSIS
       cc [flag ...] file ...  -lmalloc [library ...]

       #include <stdlib.h>

       void *malloc (size_t size)

       void free (void *ptr)

       void *realloc (void *ptr, size_t size)

       void *calloc (size_t nelem, size_t elsize)

       #include <malloc.h>

       int mallopt (int cmd, int value)

       struct mallinfo mallinfo (void)

       #include <alloca.h>

       char *alloca(int size);

DESCRIPTION
       malloc and free provide a simple general-purpose memory allocation
       package.  It is found in the library ``malloc'', and is loaded if the
       option ``-lmalloc'' is used with cc(1) or ld(1).

       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, and its contents have been destroyed (but see
       mallopt below for a way to change this behavior).  If ptr is a null
       pointer, no action occurs.

       Undefined results occur if the space assigned by malloc is overrun or
       if some random number is handed to 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 ptr is a
       null pointer, realloc behaves like malloc for the specified size. If
       size is zero and ptr is not a null pointer, the object it points to
       is freed.

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

       mallopt provides for control over the allocation algorithm.  The
       available values for cmd are:

        M_MXFAST
               Set maxfast to value.  The algorithm allocates all blocks
               below the size of maxfast in large groups and then doles them
               out very quickly.  The default value for maxfast is 96.

        M_NLBLKS
               Set numlblks to value.  The above mentioned ``large groups''
               each contain numlblks blocks.  numlblks must be greater than
               0.  The default value for numlblks is 100.

        M_GRAIN
               Set grain to value.  The sizes of all blocks smaller than
               maxfast are considered to be rounded up to the nearest
               multiple of grain.  grain must be greater than 0.  The
               default value of grain is the smallest number of bytes that
               will allow alignment of any data type.  Value will be rounded
               up to a multiple of the default when grain is set.

        M_KEEP Preserve data in a freed block until the next malloc,
               realloc, or calloc.  This option is provided only for
               compatibility with the old version of malloc and is not
               recommended.

       These values are defined in the malloc.h header file.

       mallopt may be called repeatedly, but may not be called after the
       first small block is allocated.

       mallinfo provides instrumentation describing space usage.  It returns
       the structure:

              struct mallinfo  {
                   int arena;      /* total space in arena */
                   int ordblks;    /* number of ordinary blocks */
                   int smblks;     /* number of small blocks */
                   int hblkhd;     /* space in holding block headers */
                   int hblks;      /* number of holding blocks */
                   int usmblks;    /* space in small blocks in use */
                   int fsmblks;    /* space in free small blocks */
                   int uordblks;   /* space in ordinary blocks in use */
                   int fordblks;   /* space in free ordinary blocks */
                   int keepcost;   /* space penalty if keep option */
                                   /* is used */
              }

       This structure is defined in the malloc.h header file.

       Each of the allocation routines returns a pointer to space suitably
       aligned (after possible pointer coercion) for storage of any type of
       object.

       alloca allocates size bytes of space in the stack frame of the
       caller.  This temporary space is automatically freed on return.
       alloca is only supported by the GNU C language compiler.

SEE ALSO
       brk(2), malloc(3C), gcc(1).

DIAGNOSTICS
       malloc, realloc, and calloc return a NULL pointer if there is not
       enough available memory.  When realloc returns NULL, the block
       pointed to by ptr is left intact.  If mallopt is called after any
       allocation or if cmd or value are invalid, non-zero is returned.
       Otherwise, it returns zero.

NOTES
       Note that unlike malloc(3C), this package does not preserve the
       contents of a block when it is freed, unless the M_KEEP option of
       mallopt is used.

       Undocumented features of malloc(3C) have not been duplicated.

       Function prototypes for malloc, realloc, calloc and free are also
       defined in the <malloc.h> header file for compatibility with old
       applications. New applications should include <stdlib.h> to access
       the prototypes for these functions.


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