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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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     You can let the heap allocate memory from unused stack space by
     linking your program with VARSTCK.OBJ. This file allows the near
     memory allocation functions to allocate items in unused stack
     space if they run out of other memory. The near memory allocation
     functions are _nmalloc, _nrealloc, _nexpand, and _ncalloc in all
     memory models, and malloc, realloc, _expand, and calloc in small
     data models (small and medium memory models).
 
     Programs compiled and linked under Microsoft C run with a fixed
     stack size (default size is 2K). The stack resides above static
     data, and the near heap uses space left above the stack. However,
     for some programs a fixed-stack model may not be ideal. Having the
     stack and heap compete for space may be more appropriate. Use
     VARSTCK.OBJ to do this. When the heap runs out of memory, it uses
     available stack space until it reaches the top of the stack.
 
     Be aware of the following:
 
        ■ The stack cannot grow beyond the last heap item allocated in
          the stack or, if no heap items are in the stack, beyond the
          size set at link time.
 
        ■ Once any part of stack memory is incorporated into the near
          heap, it can never be used as stack space again.
 
        ■ While the heap can employ unused stack space, the stack
          cannot take unused heap space.
 
     When using VARSTCK.OBJ, be wary of suppressing stack checking,
     which is done with the #check_stack pragma or with the /Gs or /Ox
     option. Stack overflow can occur more easily in programs that
     suppress stack checking, possibly causing errors that are
     difficult to detect.
 
     The following command line compiles TEST.C, then links the
     resulting object module with VARSTCK.OBJ. Use the /NOE option to
     avoid multiple symbol definitions. For example,
 
          qcl test.c varstck /link /NOE
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