Re: Colored output

[Bruno Haible]

Hi Akim,

> There's something which is not quite clear to me: is it supported to mix
> the ostream based interface with the regular FILE* one?

If you have an ostream_t and a FILE* and they have different destinations
(for example, one writes to stdout and the other one to a file), there is
no problem: you can use them simultaneously.

If you have an ostream_t and a FILE* that have the same destination and
you want to use them simultaneously, then there are two problems:
  1) The ostream_t is buffered, and the FILE* stream as well. To avoid
     that the output mixed up in ugly ways, you would need to
       - flush the ostream_t and its underlying stream, if any (e.g. for
         a file_ostream_t, call fflush() on the underlying FILE* stream),
       - flush the FILE* stream, through fflush().
  2) The term_ostream_t outputs escape sequences for text attributes.
     Currently the only ways to force it to go back to the initial state
     are: the output of a newline, and ostream_free().
     Therefore, in order to avoid that the FILE* stream output gets shown
     in an undesired color, you'll need to either output a newline or
     close/free the term_ostream_t first, then do the output through the
     FILE* stream.

> My initial motivation is to support colored diagnostics, which are built
> by tons of fprintf to stderr.  Currently libtextstyle does not support
> formatting primitives, and also, I don't plan to require libtextstyle.
> So I would prefer to stick to fprintf, and which a few well placed
> invocations to libtextstyle.
> 
> Is this a supported use case?  Or must (or should) everything be moved
> on top of ostreams?

If you are lucky and all your diagnostics end in a newline, you can mix
libtextstyle-enabled diagnostics with fprintf diagnostics without problem.
If you are unlucky, you need to ostream_free() the stream at the end of
every libtextstyle-enabled diagnostic.

> I don't plan to require libtextstyle.

stderr is a global variable. Similarly you may have a global variable,
guarded through #if HAVE_LIBTEXTSTYLE:

#if HAVE_LIBTEXTSTYLE
styled_ostream_t diag_stream;
#endif

and have each of your diagnostic routines be a varargs function that
initially essentially looks like this:

  #if HAVE_LIBTEXTSTYLE
  char *str = [v]asprintf (...);
  styled_stream_write_str (diag_stream, str);
  free (str);
  #else
  [v]fprintf (stderr,...);
  #endif

But now, you need to add the CSS classes somewhere. Which means that
you probably need to take that format string apart instead of doing
an asprintf().

Bruno