Tue, 20 Apr 1999 04:48:59 -0700
"David C. Hoos, Sr." <[log in to unmask]> writes:
> Matthew Heaney's solution works if the environment variable exists,
> but raises an exception if it does not.
True, but that's a consequence of the decision to return an Ada string
as the return type. Better is to return chars_ptr type, and let the
caller test the return value himself.
I illustrated how to do this in my follow-up post.
> This binding has the Boolean function
> which permits testing for existence before getting the value
> with a call to POSIX.Process_Environment.Environment_Value_Of.
This is the wrong way to use those functions, because you'd be
translating the env var twice (maybe - depends how it's implemented).
The proper way to handle this is to use the optional parameter (called
"Default", I think) of Env_Val_Of, to specify the value to return if the
env var isn't defined.
I use this technique all the time. For example,
Env_Name : constant POSIX_String := To_POSIX_String ("DELAY_TIME");
Default : constant POSIX_String := To_POSIX_String ("5.0");
Env_Val_As_PString : constant POSIX_String :=
Environment_Value_Of (Env_Name, Default);
Env_Val : constant String := To_String (Env_Val_As_PString);
Delay_Time := Duration'Value (Env_Val);
You do not need to call Is_Env_Var.