Re: Opening a file vs. creating if not yet exists

[Jacob Sparre Andersen <sparre@nbi.dk>]

Maciej Sobczak wrote:

> I find this a bit annoying for example with log files, where the
> natural scheme should be:
> - if the file exists, open and append to it
> - if the file does not exist, create it and append to it
> 
> What is the recommended way to deal with this?
> 
> begin
>    Open (File, Append_File, "file.txt");
> exception
>    when Name_Error =>
>       Create (File, Append_File, "file.txt");
> end;
> 
> Is the above idiomatic (ie. well understood and accepted as common
> practice)?

I am certain it is well understood and commonly used, but in general
it is not advised to use exceptions in ordinary control flow.  Amado's
suggestion using Ada.Directories.File_Exists is definitely closer to
the advised practice.

The problem with both of these solutions is that they are not atomic.
POSIX.IO.Open_Or_Create is more appropriate (if you are targeting a
standards compliant operating system), since it solves the problem as
an atomic operation.

Greetings,

Jacob
-- 
"Any, sufficiently advanced, technology is indistinguishable from magic."