Re: CONST Parameter passing, varying and *varsize

[Barbara Morris <bmorris@xxxxxxxxxx>]

"Wilt, Charles" wrote:
> ...
> But, I did confirm that if you passed a varying(10) variable containing
> more than 5 characters to a procedure with a parm defined CONST
> varying(5) options(*varsize); the procedure only sees 5 chars and %len
> returns 5.
> 
> I was concerned that %len() would return 10 as CONST OPTIONS(*VARSIZE)
> usually mean the address of the variable is passed directly; but for a
> varying field, the first 2 bytes contain the current length.  The
> compiler is obviousily smart enough to handle what I was trying
> correctly, but I don't know if it is doing some sort of a substr or if
> it is moving the varying(10) data to a varying(5) temporarily.
> 
> I suppose it's also possible that %len() doesn't look at the current
> length value of a varying field, or the compiler is doing something when
> it is used with a CONST VARYING OPTIONS(*VARSIZE) field.
> 

Charles, parameter passing for CONST and VALUE parameters basically
works like an EVAL from the passed parameter to the prototyped
parameter.  If necessary the compiler will actually do an EVAL between
the passed parameter and a temporary defined like the prototyped
parameter, and then pass the temporary.  Basically, the specified
parameter is passed only when the called procedure could not detect the
difference between the specified parameter and a temporary.  (The
compiler assumes that the called procedure is going to access the
parameter's value legally with respect to the options.) 

CONST OPTIONS(*VARSIZE) doesn't necessarily say that the address of the
parameter is passed directly, even if both passed and prototyped
parameters are the same with respect to varying.  With const varying
parameters, with or without *VARSIZE: if the passed varying parameter
might have a current length that is longer than the prototyped
parameter, the compiler currently uses a temporary and always assigns
the passed parameter to the temporary.  It could, if it wanted to, check
the length, and if it was not greater, it could just pass the address of
the passed parameter.