Correct way to map C #define to version

[Sumit Raja]

Hi,

My first post here as a new D user. I am trying to interface with 
FFmpeg with D and need some guidance on how to replicate the 
version semantics in a C header. I'd like to open source the D 
modules files so I want to get this right.

FFMpeg defines a bunch of constants that are then used in the 
headers to include/exclude fields from structs.

e.g.

struct AVFilterBufferRefAudioProps {
     uint64_t channel_layout;    ///< channel layout of audio 
buffer
     int nb_samples;             ///< number of audio samples per 
channel
     int sample_rate;            ///< audio buffer sample rate
#if FF_API_PACKING
     int planar;                 ///< audio buffer - planar or 
packed
#endif
} AVFilterBufferRefAudioProps;

where FF_API_PACKING is defines as:

#define LIBAVFILTER_VERSION_MAJOR  2
#define LIBAVFILTER_VERSION_MINOR 77
#define LIBAVFILTER_VERSION_MICRO 100
.
.
.
#ifndef FF_API_PACKING
#define FF_API_PACKING                  
(LIBAVFILTER_VERSION_MAJOR < 3)
#endif

I tried to do the following:

version (V54_23_100) {
   version = FF_API_PACKING;
}

and then specify the version at the top of my D interface files:

version = V54_23_100

and define the struct as

struct AVFilterBufferRefAudioProps {
     uint64_t channel_layout;    ///< channel layout of audio 
buffer
     int nb_samples;             ///< number of audio samples per 
channel
     int sample_rate;            ///< audio buffer sample rate
version(FF_API_PACKING) {
     int planar;                  ///< audio buffer - planar or 
packed
}
}

but this resulted in the wrong size of struct when the C 
functions were called - the struct did not container the planer 
field.

Am I using version correctly? How is this done usually?

Thanks

Sumit