Question

There is a section of code from a learning resource that I am studying. I’ve come across a good bit of syntax pertaining to arrays and I would be grateful if somebody could explain them to me.

1)

AudioBufferList *bufferList;

        bufferList = (AudioBufferList *) malloc (
                                                 sizeof (AudioBufferList) + sizeof (AudioBuffer) * (channelCount - 1)
                                                 );

Line 1 here I understand. What I don’t understand is everything from sizeof on. The only value that I know for sure what it is here is channelcount. What is sizeof doing here and what size values could AudioBufferList and AudioBuffer be passing to it? Are there constant values or something?

2)


 bufferList->mNumberBuffers = channelCount;

        // initialize the mBuffers member to 0
        AudioBuffer emptyBuffer = {0};
        size_t arrayIndex;
        for (arrayIndex = 0; arrayIndex < channelCount; arrayIndex++) {
            bufferList->mBuffers[arrayIndex] = emptyBuffer;
        }

        // set up the AudioBuffer structs in the buffer list
        bufferList->mBuffers[0].mNumberChannels  = 1;
        bufferList->mBuffers[0].mDataByteSize    = totalFramesInFile * sizeof (AudioUnitSampleType);
        bufferList->mBuffers[0].mData            = soundStructArray[audioFile].audioDataLeft;

        if (2 == channelCount) {
            bufferList->mBuffers[1].mNumberChannels  = 1;
            bufferList->mBuffers[1].mDataByteSize    = totalFramesInFile * sizeof (AudioUnitSampleType);
            bufferList->mBuffers[1].mData            = soundStructArray[audioFile].audioDataRight;
        }

What does -> do?

What does size_t mean?

Also is mBuffers some sort of system constant?

Answer 1

It is not objectiveC but just C

sizeof return the size of the datatype (static by the compilator)

wikipedia reference:

• sizeof
• size_t
• pointer (->)