Re: [boost] [gsoc] Boost.Process done

Subject: Re: [boost] [gsoc] Boost.Process done
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-09-13 07:28:49

Ilya Sokolov wrote:
> "Stewart, Robert" <Robert.Stewart_at_[hidden]> wrote:
> >
> > The problem with the suggested approach is that Windows winds up
> > with runtime errors if the child_fileno argument exceeds the
> > range.  It would be better to make that a compile time error.
> > The only way to do that is to use a template with the fileno
> > being a template argument.
>
> enum std_fileno { stdin, stdout, stderr }
> #ifdef _WIN32
>   typedef std_fileno fileno;
> #else
>   typedef int fileno;
> #endif
>
> void foo(fileno);
>
> foo(stdout) // ok
> foo(1) // ok on posix, compile error on windows

That's not bad, but it isn't sufficient.  The file number may be generated as a small non-negative integer from various sources, even if it is 0, 1, or 2.  The enumerators are initialized with the right values, but other values or integers (int or literals) cannot then be used.

A file_number class could be defined that converts from integer and throws an exception on negative or too-large values.  0, 1, and 2 could be guaranteed to not fail at runtime on POSIX and Windows, of course.  Static instances for stdin, stdout, and stderr could be provided to avoid the runtime range check, if they prove valuable.

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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