On Fri, 27 May 2022 at 16:23, Niall Douglas via Liaison
<liaison_at_[hidden]> wrote:
>
> Dear WG14/WG21 liason,
>
> Last WG14 meeting N2857: C2x fopen("x") and fopen("a") v2 was discussed,
> and the committee sought wording refinements and the removed second half
> of fopen("x") to be supplied as a new fopen option, for which I have
> chosen "p".
>
> As time is running short for the C23 IS, can I get feedback on proposed
> wording for the C23 IS on the following, which will also affect C++
> iostreams:
>
>
> fopen("x"):
>
> Opening a file with exclusive mode (\code{'x'} as the last character in
> the mode argument) fails if the file already exists or cannot be
> created. The check for the existence of the file and the creation of the
> file if it does not exist is atomic with respect to other threads and
> processes. If the implementation is not capable of performing the check
> for the existence of the file and the creation of the file atomically,
> it shall fail setting \code{errno} to \code{ENOTSUP} instead of
> performing a non-atomic check and creation.
>
> [Main change: Removal of second choice of implementation, which no major
> implementation chose in any case]
>
>
> fopen("a"):
>
> Opening a file with append mode (\code{'a'} as the first character in
> the mode argument) causes all subsequent writes to the file to be forced
> to the current end-of-file at the point of buffer flush or actual
> write}, regardless of intervening calls to the \code{fseek},
> \code{fsetpos}, or \code{rewind} functions. Incrementing the current
> end-of-file by the amount of data written is atomic with respect
> to other threads writing to the same file provided the file was also
> opened in append mode. If the implementation is not capable of
> incrementing the current end-of-file atomically, it shall fail setting
> \code{errno} to \code{ENOTSUP} instead of performing
> non-atomic end-of-file writes.} In some implementations, opening a
> binary file with append mode (\code{'b'} as the second or third
> character in the above list of \code{mode} argument values) may
> initially position the file position indicator for the stream beyond the
> last data written, because of null character padding.
>
> [Main change: increment of end of file to become atomic]
>
>
> fopen("p"):
>
> Opening a file with private mode (\code{'p'} as the last character in
> the mode argument) creates a file whose contents no other thread nor
> process can access via the filing system at any point in time, and whose
> entry may or may not appear in the filing system (that is, the value of
> \code{filename} may be ignored by implementations except to identify
> which storage ought to hold the file). If the implementation is not
> capable of creating private files, it shall fail setting \code{errno} to
> \code{ENOTSUP}.
>
> [Main change: this is new, it is a specific choice of implementation for
> the formerly second choice of implementation of C11 fopen("x")]

Why "filing system"? Don't we all call them file systems?

Can you briefly explain what existing practice the new "p" flag is based on?