CAFAudioDescription成员类型和端序

CAFAudioDescription 的 mSampleRate 成员是 Float64 类型,但要给它赋值,比如44100.0,我需要先将它转换为big-endian。功能 CFConvertFloat64HostToSwapped 返回a CFSwappedFloat64 哪个是 uint64_t 不 浮动64 .

为什么它返回一个int类型?我甚至不能把它当作 浮动64 .

    // required file header
    CAFFileHeader fileHeader;
    fileHeader.mFileType = CFSwapInt32HostToBig('caff');
    fileHeader.mFileVersion = CFSwapInt16HostToBig(1);
    fileHeader.mFileFlags = CFSwapInt16HostToBig(0);

    // required chunk header for audio description chunk below
    CAFChunkHeader audioHeader;
    audioHeader.mChunkType = CFSwapInt32HostToBig('desc');
    audioHeader.mChunkSize = sizeof(CAFAudioDescription);

    // required first chunk
    CAFAudioDescription audioChunk;
    audioChunk.mSampleRate = CFConvertFloat64HostToSwapped(44100.0); // type mismatch