Re: Parameter evaluation order

["William D. Ghrist" <ghristwd@pgh.net>]

Mark.Rutten@dsto.defence.gov.au wrote:
> 
> I'm using GNAT3.09 on WindowsNT (and also Solaris, but I didn't get
> this problem).
> 
> I compiled a procedure call similar to the following
> 
>   proc(func_one,func_two);
> 
> The program relies on func_one being called _before_ func_two. But
> at run-time the code above did the opposite! Is this a bug (and if so, has it
> been fixed in 3.10)? Or is there something written in the language definition
> to justify this behaviour?
> 
> Thanks,
> Mark Rutten
> 
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Yes, it is a bug in your program.  The order of execution of parameters
is not defined (this is true in other languages besides Ada, as well). 
This is one of the reasons that it is considered poor practice to write
functions with side effects.  If you must use functions with side
effects that result in situations like your example, then the valid way
to proceed is to invoke the functions first, storing their return values
in variables, then to call the procedure with the variables as
parameters.

Regards,
Bill Ghrist