Specifications

Chapter 14. Statement Reference
322
Description:
■ Creating a user-defined function
SUB...END SUB creates a user-defined function. The function definition block
between
SUB and END SUB is a set of some statements and functions.
• 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
subroutines.
•
SUB...END SUB functions can be recursive.
•
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
SUB...END SUB statement block or used as a dummyparameter of any other
function in the same program, then it will be independently treated.
• In user-defined functions, you can call other user-defined functions. You can nest
SUB...END SUB statements to a maximum of 10 levels.
• When using the
SUB...END SUB 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 local variables whose current values are avail-
able only in that function definition block, unless
PRIVATE or GLOBAL statement
is used.
•
EXIT SUB exits the function block prematurely and returns control to the position
immediately after the statement that called the user-defined function.
• Unlike other user-defined functions,
SUB function cannot assign a return value.
■ Calling a user-defined function
CALL statement and subname call a user-defined function. CALL can be omitted.
• 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")