Re: Passing Parameter as Variable vs as address of variable

On 2023-08-25 6:14 p.m., Barbara Morris wrote:

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

I just want to clarify that my statement about "pass by value" is only about the general badness of passing the address of a variable by value vs passing the variable itself by reference. And that's only a problem for RPG and other languages that don't have typed pointers.

In general, passing parameters by value can be useful. Even passing pointers by value can be useful sometimes.

I also want to clarify that when calling a program, where parameters are always passed by reference, passing a pointer-to-a-variable by reference is slower than passing the variable by reference.

dcl-pr mypgm1 extpgm;
salary packed(9:2);
end-pr;

dcl-pr mypgm2 extpgm;
salary_ptr pointer;
end-pr;

dcl-s salary packed(9:2);

For this call to mypgm1, the compiler puts %ADDR(SALARY) on the parameter stack.
mypgm1 (salary);

For this call to mypgm2, the compiler puts %ADDR(SALARY) into a temporary pointer and then it puts the address of the temporary pointer on the parameter stack.
mypgm2 (%addr(salary)); // The compiler

When mypgm1 is running, to use the SALARY parameter, the compiler dereferences the parameter-pointer to access the packed(9:2) data.

When mypgm2 is running, to use the SALARY parameter, the compiler first dereferences the parameter-pointer to get the pointer to the packed(9:2) data and then it dereferences that pointer to access the packed(9:2) data.