Re: Passing a Char to a Varchar in RPGLE Procedure Interface

["Wilson, Jonathan" <piercing_male@xxxxxxxxxxx>]

On Mon, 2014-09-29 at 02:32 -0500, Scott Klement wrote:
> Alan,
>
> You'd be correct if this was only being called from RPG.  It's actually 
> the prototype in RPG that will do this for you, it will convert to 
> another data type.  (And it doesn't have to be by value, it can be 
> either value or CONST reference)
>
> However, that's not at all true when calling from CLLE -- which Mike 
> explicitly said that he wanted.
>
> The CL compiler can't automatically change the data type of the 
> variable, because it doesn't know which data type the RPG procedure is 
> expecting...  How could it, if there's no prototype to tell it what the 
> data type should be?!
>
> However, there are ways to do what Mike is looking for, but they are not 
> quite as elegant.
>
> 1) You can use operational descriptors to find out the type of data 
> passed. Then, you can treat it accordingly (for example, you could use a 
> pointer to map the parameter to a variable with the appropriate data type.)
>
> 2) This is risky, but...  a VARYING ("VarChar" is the SQL term) field 
> will have a 2 or 4 byte prefix containing the length.  Bytes that make 
> up characters are almost always x'40' or higher.  So for parameters with 
> a short max length, if the first byte is < x'40', then it's probably a 
> VARYING parameter, if it's x'40' or higher it's a fixed-length 
> character.  Otherwise, it's a varying field.

I'm curious, how does it determine if it should be 2 or 4 bytes? Is it
based on the data type, ie DBCS, SBCS, etc also what is to stop a single
procedure being called by 2 programs with differing length of data (2v4)
bytes or does the prototyping prevent that so if it, the prototype,
knows it should be 4 bytes it enforces the caller to encode 4 bytes?