EXTRN            Define external                                    Directive

  EXTRN definition [, definition ]...

    Indicates that a symbol is defined in another module. definition
    describes a symbol and has the following format:

       [language] name [[count1]] :complex_type [:count2]

    - language specifies that the naming conventions of C, CPP, PASCAL,
      BASIC, FORTRAN, NOLANGUAGE, or PROLOG are to be applied to symbol
      name; temporarily overrides language set with a MODEL statement
    - name is the symbol that is defined in another module (must be
      declared as GLOBAL, PUBLIC, or PUBLICDLL in order for your program
      to link properly) and can optionally be followed by:
    - count1, an array element multiplier that defaults to 1
    - complex_type must match the type of the symbol where it's defined
      (the ABS type is used for symbols that represent absolute numbers)
    - count2 specifies how many items this external symbol defines
      and defaults to one if not specified.

    Examples:   EXTRN memptr:DWORD
                EXTRN C carray[32]:WORD:400


    You can use the EXTRN directive either inside or outside a segment
    declared with the SEGMENT directive. If you place EXTRN inside a
    segment, you are informing the assembler that the external variable is
    in another module but in the same segment. If you place the EXTRN
    directive ouside of any segment, you are informing the assembler that
    you don't know which segment the variable is declared in.

    In MASM mode, external symbols declared outside of any segment are
    presumed to be reachable via the DS register, which may not always be
    a valid assumption. Make sure that you either place the correct
    segment value in DS, or use an explicit segment override when
    referring to these variables.

    In Ideal mode, Turbo Assembler correctly checks for whether the
    external variable is addressable using any of the current segment
    registers, as described with the ASSUME directive.