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documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.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►
──────────────────────────────────────────────────────────────────────────────
DECLARE is a non-executable statement that declares references to BASIC
procedures and ensures argument type checking.
 
DECLARE {FUNCTION | SUB} name [([parameterlist])]
    ■ The argument name is limited to 40 characters. FUNCTION procedure
      names can end in one of the type-declaration characters
      (%, &, !, #, @, or $) to indicate the type of value returned.
    ■ The parameterlist serves as a prototype for checking the
      number and type of the arguments in SUB and FUNCTION procedure calls.
      Only the number and type of the arguments are significant. It has the
      following syntax:
 
        [BYVAL] variable[AS type][,[BYVAL] variable[AS type]]...
 
          BYVAL       Defines the variable as being passed by value
                      rather than by reference (the default). BYVAL
                      can be used only with simple numeric types (INTEGER,
                      LONG, SINGLE, DOUBLE, or CURRENCY).
          variable    Any valid BASIC variable name. If the variable is an
                      array, it can be followed by the number of dimensions
                      in parentheses, as in this fragment:
 
                      DECLARE SUB DisplayText (A(2) AS STRING)
                      DIM Text$(100,5)
                      .
                      .
                      .
                      CALL DisplayText(Text$())
 
                      The number of dimensions is optional.
 
          type        Is INTEGER, LONG, SINGLE, DOUBLE, CURRENCY, STRING,
                      or a user-defined type. Again, only the number and
                      types of arguments are significant.
 
                      A variable's type also can be indicated by including
                      an explicit type character (%, &, !, #, @, or $) or
                      by relying on the default type.
 
Usage Notes
    ■ If a parameter is passed by reference, any change to the parameter's
      value inside the procedure changes its value in the calling program.
    ■ If a parameter is passed by value, any changes to the parameter's
      value inside the procedure is local to that procedure and does not
      affect its value in the calling program.
    ■ For calls within BASIC, the DECLARE statement is required only if
      you call SUB procedures without the CALL keyword, or if you invoke
      a FUNCTION procedure defined in another module. For more information
      about invoking procedures without CALL, see Chapter 2, "SUB and
      FUNCTION Procedures" in the Programmer's Guide.
    ■ A DECLARE statement also causes the compiler to check the number
      and type of arguments used to invoke the procedure. QBX automatically
      generates DECLARE statements when you save your program while working
      in the environment. The DECLARE statement can appear only in
      module-level code (not in a SUB or FUNCTION procedure) and affects
      the entire module.
    ■ The form of the parameter list determines whether or not argument
      checking is done, as shown in the following list:
 
      Declaration                     Meaning
      ═════════════════════════════   ═══════════════════════════════════════
      DECLARE SUB First               You can omit the parentheses only if
                                      the SUB or FUNCTION procedure is
                                      separately compiled. No argument
                                      checking is done.
      DECLARE SUB First ()            First has no parameters. Arguments
                                      in a call to First generate an error.
                                      An empty parameter list indicates
                                      that the SUB or FUNCTION procedure
                                      has no parameters and that argument
                                      checking should be done.
      DECLARE SUB First (X AS LONG)   First has one long-integer parameter.
                                      The number and type of the arguments
                                      in each call or invocation are
                                      checked when the parameter list
                                      appears in the DECLARE statement.
 
Important
    ■ You cannot have fixed-length strings in DECLARE statements.
      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.
    ■ You can have arrays containing fixed-length strings in DECLARE
      statements. The lengths of the array in the CALL statement and the
      declaration must match.