[FFmpeg-devel] [PATCH] avutil/channel_layout: make pre-defined channel layouts C++ friendly

[James Almer]

On 8/16/2023 12:44 PM, Zhao Zhili wrote:
> From: Zhao Zhili <zhilizhao at tencent.com>
> 
> C++ doesn't support designated initializers until C++20. We have
> a bunch of pre-defined channel layouts, the gains to make them
> usable in C++ exceed the losses.
> 
> Signed-off-by: Zhao Zhili <zhilizhao at tencent.com>
> ---
>   libavutil/channel_layout.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
> index f345415c55..817a5ad370 100644
> --- a/libavutil/channel_layout.h
> +++ b/libavutil/channel_layout.h
> @@ -359,7 +359,7 @@ typedef struct AVChannelLayout {
>   } AVChannelLayout;
>   
>   #define AV_CHANNEL_LAYOUT_MASK(nb, m) \
> -    { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = (nb), .u = { .mask = (m) }}
> +    { AV_CHANNEL_ORDER_NATIVE, (nb), { m }, NULL }

Comment out the field names instead of removing them altogether, and add 
a comment about how this is done for the sake of c++ projects including 
this header.

>   
>   /**
>    * @name Common pre-defined channel layouts
> @@ -397,7 +397,7 @@ typedef struct AVChannelLayout {
>   #define AV_CHANNEL_LAYOUT_STEREO_DOWNMIX    AV_CHANNEL_LAYOUT_MASK(2,  AV_CH_LAYOUT_STEREO_DOWNMIX)
>   #define AV_CHANNEL_LAYOUT_22POINT2          AV_CHANNEL_LAYOUT_MASK(24, AV_CH_LAYOUT_22POINT2)
>   #define AV_CHANNEL_LAYOUT_AMBISONIC_FIRST_ORDER \
> -    { .order = AV_CHANNEL_ORDER_AMBISONIC, .nb_channels = 4, .u = { .mask = 0 }}
> +    { AV_CHANNEL_ORDER_AMBISONIC, 4, { 0 }, NULL }
>   /** @} */
>   
>   struct AVBPrint;

This needs a minor bump IMO. Something said c++ projects can look for 
before using these defines.