Re: Passing Parameter as Variable vs as address of variable

Hi Patrik

I think you might be used to programming in C or C++ - in those languages, parameters are passed by value, by default. To pass by reference, you have to prefix the parameter name with an asterisk. As you know.

In IBM i languages, CL and RPG (I don't know about COBOL), the default is that parameters are passed by reference. This is automatic, unless you specify "by value".

So it is extremely _*not*_ recommended to pass a pointer (by value). You completely lose any data type checking when compiling that program.

Also, you cannot define an RPGLE program to have an incoming parameter passed in by value - so all RPG (and CL) programs expect to receive a pointer to whatever parameter is listed. I just verified this, both with the default MAIN procedure that uses the cycle and with a MAIN control-option where you specify a procedure the does not use the cycle.

Cheers
Vern

On 8/26/2023 10:51 AM, Patrik Schindler wrote:

Hello Barbara,

Am 26.08.2023 um 00:14 schrieb Barbara Morris<bmorris@xxxxxxxxxx>:

If you're asking about passing the address of a variable by value vs passing the variable by reference ...

They both behave the same, with the same performance.

When looking at your assertion from a "modern hardware" point of view, counting wall clock time, I agree. The difference is negligible. Double the amount of some µs is still some µs. Too fast for a human being to be detected.

When looking at power efficiency and counting CPU cycles, I assert that handling pointers is in almost any case more efficient (needing less CPU cycles) than actually duplicating data in RAM. Especially when the data exceeds the size of a pointer.

For that I also prefer to use pointers wherever possible. But…

But passing a variable by reference is generally good and passing its address by value is generally bad.

If this was the case, why is there the possibility to pass by reference at all?

A use case for me to "pass by value" is to "write protect" a variable. The called application now can alter the variables' contents at will. It won't get changed for the calling application.

But maybe there are other ways to get the described "readonly" feature.

:wq! PoC