PRODUCT  :  Borland C++                           NUMBER  :  1563
  VERSION  :  3.x
       OS  :  All
     DATE  :  October 25, 1993                         PAGE  :  1/3

    TITLE  :  Allocating data >64K with the keyword huge




  The segmented architecture of the 80x86 processor is not well-
  suited for data structures that are of a size equal to or greater
  than 64K, more precisely 65536 bytes.  To ease the programing
  difficulties caused by this limitation of the processor, Borland
  has implemented the "huge" keyword in association with pointers.


  Dynamic Allocation
  ------------------

     The typical syntax for dynamic allocation in C is

         char huge *BigArray = (char huge *) farmalloc(120000L);
         char huge *BigArray = (char huge *) farcalloc(120000L);

     Similarly, the huge keyword can be used with new in C++:

         char huge *BigArray = new huge char[120000];


  Static Allocation
  -----------------

         In DOS, these data structures can also be allocated
     statically in the DGROUP.  For example,

         char huge BigArray[120000L];

         int main(void)
         {
             return 1;
         }

     Because the huge keyword implies a data structure greater than
     64K and the stack is limited to 64K, you cannot allocate a
     huge data structure locally unless it is declared static.
     Remember that static local variables are placed in the data
     segment, not on the stack. For example:

         int main(void)
         {
             char huge BigArray[120000L];        // ERROR!!!
             static char huge BigArray[120000L]; // LEGAL













  PRODUCT  :  Borland C++                           NUMBER  :  1563
  VERSION  :  3.x
       OS  :  All
     DATE  :  October 25, 1993                         PAGE  :  2/3

    TITLE  :  Allocating data >64K with the keyword huge




             return 1;
         }

     Because of complications produced by the Windows' loader,
     static allocation of huge data structures is not supported in
     Windows.


  Memory Models
  -------------

     Huge data structures can be allocated dynamically in all
     memory models except for tiny.  However this implies that the
     data is far ( i.e. is in a segment other than DS ).  For the
     small and medium memory models in DOS, your application must
     use functions that assume far data when manipulating the
     elements of the structure.  Also, you must use the far keyword
     in your class declaration in these two memory models in DOS.
     This also applies to Windows.

     Note that the huge memory model does _NOT_ imply huge
     pointers.


  Element Size
  ------------

     The elements of the huge array must have a size that is a
     power of 2 ( i.e. 2, 4, 8, 16, 32, etc. ).  This ensures that
     no individual element overlaps a segment boundary.  Though the
     compiler can handle element access of arrays greater than 64K,
     the code generated cannot deal with the case of an array
     element that straddles a segment boundary.


  Multi-dimensional Arrays
  ------------------------

     The syntax for declaring a multi-dimensional array is the same
     as that of a single dimension array if no dimension of the
     array by itself requires greater than 64K.  For example,

         unsigned (huge *Array2)[100] =













  PRODUCT  :  Borland C++                           NUMBER  :  1563
  VERSION  :  3.x
       OS  :  All
     DATE  :  October 25, 1993                         PAGE  :  3/3

    TITLE  :  Allocating data >64K with the keyword huge




           new huge unsigned[1000][100];

     Complications arise dynamically allocating multi-dimensional
     arrays with new if any one dimension of the array is itself
     greater than 64K.  For example,

         unsigned huge (huge *Array4)[40000L] =
           new huge huge unsigned[4][40000L];

     Syntax for static allocation is the same as the syntax for
     single dimension arrays.


  DISCLAIMER: You have the right to use this technical information
  subject to the terms of the No-Nonsense License Statement that
  you received with the Borland product to which this information
  pertains.