Constants in KCML

Numeric variables whose name begins with an underscore are presumed to be constants whose value cannot be changed after they have been declared in a DIM or COM statement. The initialization, which allows simple numeric expressions, takes place at resolve time. The value can be used in other resolve time statements provided they follow the declaration. Thus:

 DIM _BUFSIZE=8*1024 // this is legal
 // _BUFSIZE=1024    // this is not
 DIM buffer$(_BUFSIZE) // this is legal
 // DIM _SomeConstant  // this is not

For compatibility with any KCML program that uses variables with a leading underscore already as regular variables, this functionality can be enabled and disabled when programs are being compiled from source using byte 59 of $OPTIONS RUN. The HEX(01) bit must be present in this byte for constant functionality to be present. It is enabled by default (as of KCML 6.10).

As a convenience constant definitions can appear in LOCAL DIM statements when their value will be set at run time.

Constants can be defined in a library and referenced from the foreground or other libraries. They are initialized during the resolve phase so the library defining the constant must be visible at that time. Libraries that reference constants defined in other libraries should have the defining library loaded when they are saved and must be recompiled if the definition of the constant is changed.

Constants can be marked as PRIVATE when initialized in a DIM statement in a library thus limiting their visibility to the library that defined them. They can be used in functions defined in the library but they cannot be referred to directly from another library or from the foreground.

Starting with KCML 6.10 some common constants are predefined and do not need a definition. To be exact, if a constant is not defined in the foreground the library list is searched for a definition and if not found there a built in list is consulted. For more about this list see the Workbench Function Browser or this page.

The DEFRECORD statement creates a constant defining the size of the record. Thus

DEFRECORD Fred
   FLD a
   FLD b
END RECORD

DIM FredRec$_Fred