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BEGINAREA
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Purpose : Specify start of a dynamic overlay area
Syntax : BEGINAREA
The BEGINAREA command is used to specify to the linker the start of an
overlay area in the output file. Each BEGINAREA should have a
corresponding ENDAREA to indicate the end of the overlay area.
With static overlays BEGINAREAs, and therefore overlay areas, may be
nested within one another so long as there is a corresponding ENDAREA
for each BEGINAREA. This allows the developer to create a structure of
overlays within an area to use the minimum amount of memory for the
maximum number of overlay routines.
With Blinker dynamic overlays, as opposed to static overlays, the mutual
dependency of each overlay procedure or file is unimportant. Also, the
multiple nested overlay areas associated with static overlays are no
longer necessary, although multiple overlay areas may be helpful in
ordering the included libraries. The BEGINAREA and ENDAREA commands are
simply treated as markers to the beginning and end of code which is to
be overlaid.
For most compilers, the .OBJ files listed between a BEGINAREA and
ENDAREA are managed at runtime on a segment basis, i.e. the whole CODE
segment for each .OBJ is loaded into memory whenever any function or
procedure within that .OBJ file is called.
For more details on how functions and procedures may be kept in separate
segments to reduce the overlay unit size, please refer to the
appropriate compiler manual for the language being used.
All Clipper Summer '87 .OBJ files listed between a BEGINAREA and ENDAREA
are managed at runtime on a procedure or function basis, no matter how
many procedures or functions are present in the .OBJ file. Therefore
excessively large procedures and functions should be avoided. The
Clipper 5.01 dynamic paging system automatically breaks procedures down
into 1kb pages for improved execution speed.
See Also:
ENDAREA
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