Important Notice

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documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

  ◄Syntax►  ◄Details►  ◄Example►                 ◄Contents►  ◄Index►  ◄Back►
──────────────────────────────────────────────────────────────────────────────
This DECLARE statement declares calling sequences for external procedures
written in other languages. For the DECLARE statement used to declare
references to BASIC procedures, see ◄DECLARE (BASIC Procedures)►.
 
DECLARE FUNCTION name [CDECL] [ALIAS "aliasname"] [([parameterlist])]
DECLARE SUB name [CDECL] [ALIAS "aliasname"] [([parameterlist])]
    ■ The argument name can have up to 40 characters. A FUNCTION procedure
      name can include an explicit type character (%, &, !, #, @, or $)
      that indicates the type of value the procedure returns.
    ■ The CDECL passes the arguments from right to left, rather than
      using the BASIC convention of left to right. CDECL also affects the
      name used in searches of object files and libraries:
        - If there is no ALIAS clause in the DECLARE statement, the type-
          declaration character is removed from the name of the procedure,
          and an underscore is added to the beginning. This becomes the
          name used when searching libraries and external files.
        - If CDECL is used with ALIAS, aliasname is used as is.
    ■ parameterlist has this syntax:
 
       [{BYVAL|SEG}] variable [AS type][,[{BYVAL|SEG}] variable [AS type]]...
 
       BYVAL       The parameter is passed by value, rather than by
                   reference. Reference is the default. BYVAL can be used
                   only with INTEGER, LONG, SINGLE, DOUBLE, and CURRENCY
                   types. When BYVAL appears in front of a parameter, the
                   actual argument is converted to the type indicated in
                   the DECLARE statement before being passed.
       SEG         Indicates the parameter is passed as a segmented
                   address (far address).
       variable    A valid BASIC variable name. Only the variable's
                   type is significant. If the variable is an array it
                   can be followed by the number of dimensions in
                   parentheses (to maintain compatibility with older
                   versions of BASIC). For example:
 
                   DECLARE SUB EigenValue (A(2) AS DOUBLE)
 
       AS type     The variable's type. The type can be INTEGER, LONG,
                   SINGLE, DOUBLE, STRING, CURRENCY, ANY, or a user-
                   defined type. You also can indicate the variable's
                   type by including an explicit type character (%, &, !,
                   #, @, or $) in the variable name or by relying on the
                   default type. When declaring external procedures
                   written in other languages, you can use the ANY
                   keyword in the AS clause. ANY overrides type checking
                   for that argument. You cannot use ANY with arguments
                   passed by value.
 
      Note: When neither BYVAL nor SEG is used, arguments are passed as
            near addresses (offsets).
 
    ■ This form of the DECLARE statement lets you refer to procedures
      written in other languages. The DECLARE statement also causes the
      compiler to check the number and type of arguments used to invoke
      the procedure. A DECLARE statement can appear only in module-level
      code and affects the entire source file.
    ■ The form of the parameter list determines whether or not argument
      type checking is done, as described in the declarations below:
 
      Declaration                          Meaning
      ═══════════════════════════════════  ═════════════════════════════════
      DECLARE SUB First CDECL              No argument checking is done
                                           when there is no parameter list.
      DECLARE SUB First CDECL ()           First has no parameters.
                                           Arguments in a call to First
                                           generate an error. (Empty
                                           parentheses indicate that the
                                           SUB or function has no parameters
                                           and that argument checking
                                           should be done.)
      DECLARE SUB First CDECL (X AS LONG)  First takes one long integer
                                           argument. When a parameter
                                           list appears, the number and
                                           type of the arguments are
                                           checked in each invocation.
 
    ■ A procedure that appears in a DECLARE statement can be invoked
      without the CALL keyword.
 
Important
    ■ You cannot have fixed-length strings in DECLARE statements
      because only variable-length strings can be passed to SUB and
      FUNCTION procedures. Fixed-length strings can appear in an argument
      list but are converted to variable-length strings before being
      passed.
    ■ Be careful when using the SEG keyword, because BASIC
      may move variables in memory before the called routine begins
      execution. Anything in a CALL statement's argument list that causes
      memory movement may create problems. You can safely pass variables
      using SEG if the CALL statement's argument list contains only
      simple variables or arithmetic expressions.
    ■ You cannot pass arrays using the SEG keyword.