Re: Dangerous glibc byte/wide stream interactions

[Bruno Haible <haible at ilog dot fr>]

Markus Kuhn writes:

> I admit that this behaviour does not strictly violate the letter of the
> ISO C99 standard, which says in section 7.19.2
> 
> ---------------------------------------------------------------------
>        [#4]  Each  stream  has  an  orientation.  After a stream is
>        associated with an external file, but before any  operations
>        are  performed  on  it,  the  stream is without orientation.
>        Once a wide character input/output function has been applied
>        to  a stream without orientation, the stream becomes a wide-
>        oriented  stream.  Similarly,  once  a   byte   input/output
>        function  has  been applied to a stream without orientation,
>        the stream becomes a byte-oriented stream. Only  a  call  to
>        the  freopen  function  or  the fwide function can otherwise
>        alter the orientation of a stream.  (A  successful  call  to
>        freopen removes any orientation.)224)
> 
>        [#5] Byte input/output functions shall not be applied  to  a
>        wide-oriented   stream   and   wide  character  input/output
>        functions shall not be applied to  a  byte-oriented  stream.
> ---------------------------------------------------------------------
> 
> and which also requires neither the fwide() function nor the freopen
> function to be successful.

Right. This is also the reason why the fwide(3) manual page says:

       Once a stream has an orientation, it cannot be changed and
       persists until the stream is closed.

> However, I strongly argue that this behaviour makes the entire wide
> I/O system practically completely useless

It is not as useless as you might have hoped. I find fprintf with the
%lc (for a wint_t) and %ls (for a wchar_t*) directives more useful
than using fwprintf.

Some small programs can make use of wprintf, though; 'col' and 'ul',
contained in the util-linux, are examples.

> A typical program contains library modules from various sources, some of
> which will use byte-output (printf) and others will use wide-output
> (wprintf). It is *essential* that all modules can independently and
> reliably access stderr in order to issue diagnostic, warning and error
> messages.

Then they should all agree on one. Mixing printf and wprintf for the
same stream is unportable.

Bruno