malloc(3X)                                             malloc(3X)



NAME
     malloc, free, realloc, calloc, mallopt, mallinfo - provide a
     fast main memory allocator

SYNOPSIS
     #include <malloc.h>

     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;

     int mallopt(cmd, value)
     int cmd, value;

     struct mallinfo mallinfo(max)
     int max;

DESCRIPTION
     malloc and free provide a simple general-purpose memory
     allocation package, which runs considerably faster than the
     malloc(3C) 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).

     Undefined results will 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 will be unchanged up to the lesser of
     the new and old sizes.

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



January 1992                                                    1

malloc(3X)                                             malloc(3X)



     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 0.

     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 */
     }





2                                                    January 1992

malloc(3X)                                             malloc(3X)



     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.

STATUS MESSAGES AND VALUES
     The malloc, realloc, and calloc programs 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.

WARNINGS
     This package usually uses more data space than malloc(3C).
     The code size is also bigger than malloc(3C).
     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.

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






























January 1992                                                    3