fWritePtr
if (bytes > fSize - fWritePtr) {
size_t len = fSize - fWritePtr;
memcpy(fData + fWritePtr, dataPtr, len);
memcpy(fData + fWritePtr, dataPtr, bytes);
fWritePtr = (fWritePtr + bytes) % fSize;
fWritePtr = 0;
int fWritePtr;