[fpc-pascal] Why opening a file for write fails in fpc 2.6?

[Giuliano Colla]

Il 31/10/2012 14:45, Jonas Maebe ha scritto:
>
> On 31 Oct 2012, at 14:35, Giuliano Colla wrote:
>
>>
>> Understood, thank you. But shouldn't it be the other way around, i.e. 
>> one should explicitly request an exclusive lock?
>
> No, that is how the behaviour of this function is defined. Looking at 
> the documentation, is seems that file locking for Unix was already 
> implemented in FPC 2.4.0 though, so maybe that won't be the problem 
> after all.
>

Well, from the way Delphi File Mode are defined since the dawn of times, 
if you don't or fmWrite with anything, the default behavior is to open 
in fmShareCompat mode (=0), a legacy DOS mode tied to the long time dead 
FCB inherited from CP/1, which, to my knowledge, doesn't grant an 
exclusive lock, and which has no Unix equivalent. IMHO opinion it would 
be more reasonable to map this mode to a plain non-locking mode, in Unix 
environment.

>
>> but if it doesn't it's a Delphi bug, I'd say. What are exceptions 
>> there for, if not for telling you that what you requested cannot be 
>> done?
>
> There are multiple ways to indicate a failure. Exceptions are a very 
> expensive way for doing so, and generally should only be used in cases 
> that are truly exceptional and/or indicate a fatal error. In other 
> cases, using a special return value is generally much more appropriate.
>
>
My bad. I hadn't realized that low level file operation such as FileOpen 
and FileCreate do not raise an exception on failure. I seldom use them, 
and only in connection with physical devices, where I always take care 
to verify the existence before attempting to read or write. So I just 
relied on a useless try-except construct.
It's very unlikely that such a failure would permit a program to 
continue running, I'd call it a fatal error, so an exception would be 
welcome, but that's life...

Giuliano