Re: Basic c question again - type casting

[Barbara Morris <bmorris@xxxxxxxxxx>]

Lim Hock-Chai wrote:
> Barbara, 
> I'm a bit lost.  You say my RPG prototype should be 10A, not *string.
> But your example showing RPG protype with *string.  

If you want your callers to pass you 10A or 2048A with trailing blanks, 
then the RPG prototype should say that, and be 10A.  And the C typedefs 
should also be 10 bytes long, using your structs.

But I think it would be better if you changed your procedure so it 
didn't require your callers to pass 10A or 2048A with trailing blanks. 
Instead, require them to pass a null-terminated string.  Your procedure 
can then get the blank-filled 10A or 2048A value quite easily from the 
null-terminated parameters, using %STR.

> I really prefer to do 
>   typedef struct {        
>       char value[10];     
>   } logECD_STP3_piModuleName_T;
>
> But I don't want to have to do below in c just to call a function:
> memset(&piModuleName, ' ', sizeof(piModuleName));
> memcpy(&piModuleName, "MYMODULE",8);
> logECDSTP3(piModuleName...)
>
>        
> I want to do this, hence, I changed it to use *string
> logECDSTP3("MYMODULE", ...)
>
> Clear as mud?

Crystal clear.  Basically, you have a trade-off between the convenience 
of coding your procedure, and the convenience of calling your procedure. 
  Your procedure needs a 10A with trailing blanks, so you are putting a 
requirement on your caller to pass it exactly the way you need it.

If you only have RPG callers, there's no difference in the convenience 
of calling; the call is the same for 10A and for * options(*string). 
But for a C caller, you have seen how awkward it is to pass a 10A parameter.

As a rule of thumb, favour the convenience of your callers.  You only 
write the procedure once, but you might call it many times.  So it's 
worth taking a bit of extra trouble in the procedure or a bit of extra 
trouble choosing prototype keywords, if it makes it easier to call the 
procedure.

In this case, it's only a tiny bit of extra trouble.