如何创建指向结构的指针并进行类型转换？

Question

can someone tell me where I'm going wrong here? I'm trying to create a pointer to the struct aqData that is passed in to the function, and type type cast it to a struct type of AQPlayerState.

I'm getting the errors - Use of undeclared identifier "AQPlayerState" and Expected expression

    @implementation AudioPlayer

#define kNumberBuffers 3

struct AQPlayerState {
    AudioStreamBasicDescription   mDataFormat;
    AudioQueueRef                 mQueue;
    AudioQueueBufferRef           mBuffers[kNumberBuffers];
    AudioFileID                   mAudioFile;
    UInt32                        bufferByteSize;
    SInt64                        mCurrentPacket;
    UInt32                        mNumPacketsToRead;
    AudioStreamPacketDescription  *mPacketDescs;
    bool                          mIsRunning;
};

static void HandleOutputBuffer (
                                void                *aqData,
                                AudioQueueRef       inAQ,
                                AudioQueueBufferRef inBuffer
                                ) {

    struct AQPlayerState *pAqData = (AQPlayerState *) aqData;

Thanks in advance for any help

Answer 1

I believe Objective-C behaves as C . If it doesn't this might not apply to Objective-C .

structs in C are recognized by their "full name". Try

  struct AQPlayerState *pAqData = (struct AQPlayerState *) aqData; 

or , even better , don't cast at all. The C compiler knows how to convert from void* to any other pointer to object

    struct AQPlayerState *pAqData = aqData;

• implicit conversion: good
• explicit conversion (cast): not so good