[fpc-pascal]exception handling

[Thomas Schatzl]

Subject: [fpc-pascal]exception handling


> spent a few moments going over the docs in the manual re: exception
> handling. for some reason it just doesn't seem to be sinking in, as
> nothing i've tried as of yet has managed to stop prog from crashing when
> data in input that's of a different type than program is expecting
> (string as opposed to integer, for example).
>
> as i said, i'm pretty sure that its something really small and obvious,
> i'll include a few lines here ... maybe someone can spot my mistake ...
> pretty sure its the EConvertError and that there's a pre-defined error
> type that I just haven't come across yet.
>
>         try
>             readln(NewAlbum.Year);
>         except
>             on EConvertError do NewAlbum.Year := 0;
>         end;

- did you include the sysutils unit?
- afaik readln just raises runtime error which is unspecified according to
the docs; eventually an EIOError (or similar if this does not exist) because
this behaviour can be turned on/off with $I+/-.
But to be sure, you might want to catch general exceptions.
- do the following:

s: String;
i : Integer;
code : Word;

try
    readln(s);
    i := StrToInt(s);
catch
    on EIOError ...
end;

or

    {$I-}
    readln(i);
    {$I+}
    if (IOResult <> 0) then ... // IOResult (hopefully) contains an error
number in case of an I/O error

or

    readln(s);
    val(s, i, code);
    if (code <> 0) then Error...

But this has not been verified but it should be about right....

Regards,
  Thomas