best practice: error handling

[milouz <a.michelizza@gmail.com>]

Hi,

I'm wondering about the best way to handle errors in Ada when calling
a function/procedure that may fails.

For example, when programming on Unix systems in C, the called
functions usually return a zero or positive value on success and -1 on
failure, while setting a global variable (errno) to give some
informations about the failure.

What's the best way to deal with that kind of error in Ada ?
Throwing an exception ? Returning some error code ? Passing a special
parameter ?...