Re: #pragma once in ISO standard yet?

James Kanze <>
Wed, 19 Dec 2007 09:09:10 CST
On Dec 19, 12:09 am, ("Andrei
Alexandrescu (See Website For Email)") wrote:

James Kanze wrote:

On Dec 18, 7:59 am, ("Andrei
Alexandrescu (See Website For Email)") wrote:

James Kanze wrote:

You may think it's a security problem, but it's the way things
work in real life. Neither SMB nor NFS have a means of
asserting whether two pathnames are identical. So "#pragma
once" can't be made to work reliably under Windows nor under
Unix. The probability of a feature being adopted which can't be
implemented reliably under Unix nor under Windows is pretty

I guess your argument would be strengthened by you also showing a
significant necessity for projects to use multiple aliased include
search paths that resolve to the same physical directories. In the
projects I've worked on, this was always a project management blunder.

On the projects I've worked on, it has generally occured because
we used third party libraries, which in turn depended on other

How does that influence the search paths? A library depends on another,
but it does not require that it's in some specific place.

The library provides its own, identical copy. Library A is
designed so that it includes all that it needs of library B, so
you can use it without installing library B. You need library B
otherwise, however, so you have installed it. The #include in
library A finds its copy; the #include in your code finds the
separately installed copy.

Or because different people's home directories were
mounted on different file systems.

How does that lead to *different* logical search paths
resolving to *identical* physical directories?

Through various symbolic links ending up in different file
systems. It's not unusual to have identical versions of more or
less generally used tools (including libraries) installed on
several servers (perhaps by means of mounts, more often with
multiple copies). And to have a common account for files shared
in the group. (E.g. here, my home account is at
/home/team02/jakan, but I often have to link against files in
/home/team02/common. In this case, the mount point is in fact
/home/team02, but in most places I've worked, my own account
would have a separate mount.)

James Kanze (GABI Software)
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