IBM AS/400 manual Passing Prototyped Parameters

Passing Prototyped Parameters

*-------------------------------------------------------------

*The procedure returns a value of a 10-digit integer value.

*The 3 parameters are all 5-digit integers passed by value. *-------------------------------------------------------------

D MyFunc		PR	10I 0		EXTPROC('DO_CALC')
D			5I	0	VALUE
D			5I	0	VALUE
D			5I	0	VALUE
....
Figure	63. Prototype for Procedure DO_CALC with VALUE Parameters
P DO_CALC		B			EXPORT
	*-------------------------------------------------------------
	* This procedure performs a function				on the 3 numeric value￿s
	* passed to it as value parameters.				It also returns a value.
	*-------------------------------------------------------------
D DO_CALC		PI	10I 0
D	Term1		5I	0	VALUE
D	Term2		5I	0	VALUE
D	Term3		5I	0	VALUE
D Result		S	10I 0
C		EVAL	Result = Term1 ** 2 * 17
C					+ Term2	* 7
C					+ Term3
C		RETURN	Result * 45 + 23
P		E

Figure 64. Procedure Interface Definition for DO_CALC Procedure

Passing

by

Read-Only Reference

An alternative

means

of

passing a

parameter

to a

prototyped

procedur

is to pass it by

read-only

reference.

Passing

by

read-only

referenc

must

pass

the

parameter by

reference

and

you

know

that

the value

eter

will

not be changed during the call.

For example, many system AP

read-only parameters specifying formats, or lengths.

Passing

a

parameter by read-only reference

has

the

same

advantages

by value. In particular, this method allows

you to pass literals and

important,

however,

that

you

know

that the

parameter

would

not

be ch

the

call.

When a parameter is passed by read-only reference, the compiler ma parameter to a temporary field and pass the address of the tempor tions that would cause this are: the passed parameter is an expre passed parameter has a different format.

Note: If the called program or procedure is compiled using a protot guage that enforces the read-only reference method (either I prototypes, or C), then the parameter will not be changed. If program or procedure does not use a prototype, then the compi ensure that the parameter is not changed. In this case, the the prototype must be careful when specifying this parameter-pa method.

Chapter 10. Calling Programs and Procedures137