[FFmpeg-devel] bprint.h can't be included in C++ code

[wm4]

On Fri, 21 Nov 2014 21:42:35 +0100
Nicolas George <george at nsup.org> wrote:

> Le primidi 1er frimaire, an CCXXIII, Vadim Kalinsky a écrit :
> > bprint.h can't be included in C++ code
> > C++ does not support anonymous struct.
> 
> Thanks for the patch.
> 
> Basically, bprint.h is not meant to be included in c++ code.
> 
> > From a45cc83a807e7eabf158ddff52751171e80874f8 Mon Sep 17 00:00:00 2001
> > From: Vadim Kalinsky <vkalinsky at Q.local>
> > Date: Fri, 21 Nov 2014 13:39:07 -0500
> > Subject: [PATCH] C++ compatible AVBPrint definition.
> > 
> > ---
> >  libavutil/bprint.h | 16 +++++++++-------
> >  1 file changed, 9 insertions(+), 7 deletions(-)
> > 
> > diff --git a/libavutil/bprint.h b/libavutil/bprint.h
> > index d1682fc..10e96d7 100644
> > --- a/libavutil/bprint.h
> > +++ b/libavutil/bprint.h
> > @@ -30,9 +30,12 @@
> >   * Define a structure with extra padding to a fixed size
> >   * This helps ensuring binary compatibility with future versions.
> >   */
> > -#define FF_PAD_STRUCTURE(size, ...) \
> > -    __VA_ARGS__ \
> > -    char reserved_padding[size - sizeof(struct { __VA_ARGS__ })];
> 
> > +#define FF_PAD_STRUCTURE(name,size, ...) \
> > +typedef struct __pad_structure_helper_##name { __VA_ARGS__ } __pad_structure_helper_##name; \
> > +typedef struct name { \
> > +__VA_ARGS__ \
> > +char reserved_padding[size - sizeof(__pad_structure_helper_##name)]; \
> > +} name;
> 
> Apart from the fact that it makes the macro hackery vastly less readable
> (maybe some indentation would help), identifiers starting with a double
> underscode are reserved for the implementation, and therefore can not be
> used.

Oh, seeing that this struct is to be allocated on the stack, my
suggestion of using flexible array members is not very helpful; but
that makes this macro-hackery look even more questionable. All you need
is a plain old static array.

> >  
> >  /**
> >   * Buffer to print data progressively
> > @@ -74,15 +77,14 @@
> >   * internal buffer is large enough to hold a reasonable paragraph of text,
> >   * such as the current paragraph.
> >   */
> > -typedef struct AVBPrint {
> > -    FF_PAD_STRUCTURE(1024,
> > +
> > +FF_PAD_STRUCTURE(AVBPrint, 1024,
> >      char *str;         /**< string so far */
> >      unsigned len;      /**< length so far */
> >      unsigned size;     /**< allocated memory */
> >      unsigned size_max; /**< maximum allocated memory */
> >      char reserved_internal_buffer[1];
> > -    )
> > -} AVBPrint;
> > +)
> >  
> >  /**
> >   * Convenience macros for special values for av_bprint_init() size_max
> 
> Regards,
>