From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!feeder.eternal-september.org!news.unit0.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Niklas Holsti Newsgroups: comp.lang.ada Subject: Re: Determining size of Standard_Input (when file contents are piped into a program). Date: Mon, 7 Jan 2019 11:32:27 +0200 Organization: Tidorum Ltd Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Trace: individual.net lMgnWPeC/jSbyI1PKJah1Q+KCnEmwYVFk0XfvRdxcMpigGHh0Q Cancel-Lock: sha1:09XRBCVAc0mbPnxvbao9u3xOhsw= User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 In-Reply-To: Xref: reader01.eternal-september.org comp.lang.ada:55234 Date: 2019-01-07T11:32:27+02:00 List-Id: On 19-01-07 05:05 , Keith Thompson wrote: > Niklas Holsti writes: >> On 19-01-06 13:02 , Bojan Bozovic wrote: >>> Is there platform independent way to do this? I was unable to find >>> anything in RM under Ada.text_IO. >> >> I would say that this is impossible in principle. On some systems, other >> concurrent programs can write more data into the input file as your >> program is reading the file, so the input file can grow during the >> execution of the program, and may not even have any fixed upper bound on >> its size (apart from the total space available in the system). >> >> IMO the only robust way is to read all of standard input and store it >> within the program, or in a temporary file, and then process the stored >> data. > > I mostly agree, but it could be possible in some limited > circumstances. > > For example, if a program on Linux has its standard input redirected > from a file, the system still keeps track of the identity of the > file (/proc/$PID/fd/0 is a symbolic link to the file). Ah, good to know. > You can then determine the size of that file. Yep, but the file-size may grow with time and -- on some systems -- the added data may become visible (readable) to a program reading the file. But not on all systems -- I ran across this quirk when a certain multi-process application which worked under Linux did not work under Apple OS/X, because it used such a growing file to communicate data from one process (writer) to another (reader). On OS/X, the reader never saw any data that the writer wrote _after_ the reader opened the file. Of course this may also depend on the Ada run-time in some way, although in both cases GNAT was used. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ .