Denso Power Net Terminal BHT-7500 Spécifications télécharger pdf (Page 215)

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101

Chapter 14. Statement Reference

206

Description:

■ Creating a user-defined function

DEF FN creates a user-defined function.

• 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.

• The

DEF FN statement 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

subroutines.

•

DEF FN functions cannot be recursive.

• The type of

functionname should match that of the function definition

expression.

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

stringlength

for a return value. 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

expression, is a local variable valid only in that

expression . Therefore, if a variable having the same name as dummypa-

rameter

is used outside DEF FN statement or used as a dummyparameter

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

•

expression describes some operations for the user-defined function. It

should be within one program line including definition described left to the equal

sign.

•

expression can call other user-defined functions. You can nest DEF FN state-

ments to a maximum of 10 levels.

• If variables other than

dummyparameter(s) are specified in expression,

they will be treated as global variables whose current values are available.

•

stringlength should be enclosed with a pair of square brackets [ ].

■ Calling a user-defined function

FNfunctionname calls a user-defined function.

• The number of realparameters should be equal to that of dummyparame-

ter

s, and the types of the corresponding variables used in those parameters

should be identical.

• If you specify a global variable in realparameter when calling a user-defined

function, the user-defined function cannot update the value of the global variable.

This is because all realparameters are passed not by address but by value.

(So called "Call-by-value")

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