Denso Power Net Terminal BHT-7500 Dokumentacja Pobierz pdf (Strona 219)

Chapter 14. Statement Reference

210

Description:

■ Creating a user-defined function

DEF FN...END DEF creates a user-defined function. The function definition block

between DEF FN and END DEF is a set of some statements and functions.

• Definition of a user-defined function should appear preceding a calling statement

of the user-defined function in a source program.

• You cannot make double definition to a same function name.

• This statement block should not be defined in the block-structured statements

(

DEF FN...END DEF, FOR...NEXT, FUNCTION...END FUNCTION, IF...THEN...

ELSE...END

IF, SELECT...CASE...END SELECT, SUB...END SUB and WHILE

...WEND

), in the error-handling routine, event-handling routine, or in the subrou-

tines.

• DEF FN...END DEF functions can be recursive.

• In defining a character function, you can specify the maximum

stringlength.

If its specification is omitted, the default value of 40 characters takes effect.

• dummyparameter, which corresponds to the variable having the same name in

the function definition block, is a local variable valid only in that block. Therefore,

if a variable having the same name as dummyparameter is used outside DEF

FN...END

DEF statement block or used as a dummyparameter of any other

function in the same program, it will be independently treated.

• In user-defined functions, you can call other user-defined functions. You can nest

DEF FN...END DEF statements to a maximum of 10 levels.

• When using the

DEF FN...END DEF together with block-structured statements

(

DEF FN...END DEF, FOR...NEXT, FUNCTION...END FUNCTION, IF...THEN...

ELSE...END

IF, SELECT...CASE...END SELECT, SUB...END SUB and WHILE

...WEND

), you can nest them to a maximum of 30 levels.

• If variables other than

dummyparameter(s) are specified in the function defini-

tion block, they will be treated as global variables whose current values are avail-

able.

•

EXIT DEF exits the function block prematurely and returns control to the position

immediately after the statement that called the user-defined function.

• The block-format DEF FN statement should be followed by END DEF which ends

the function block and returns control to the position immediately after the state-

ment that called the user-defined function.

• Using Syntax 5 allows you to assign a return value for a function. The type of

functionname should match that of a return value. If no return value is

assigned to

functionname , the value 0 or a null string will be returned for a

numeric function or a character function, respectively.

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