Number of bytes available in the input buffer
BytesAvailable indicates the number of bytes currently available to be read from the input buffer. The property value is continuously updated as the input buffer is filled, and is set to 0 after the fopen function is issued.
You can make use of BytesAvailable only when reading data asynchronously. This is because when reading data synchronously, control is returned to the MATLAB® command line only after the input buffer is empty. Therefore, the BytesAvailable value is always 0. To learn how to read data asynchronously, see Reading Text Data.
The BytesAvailable value can range from zero to the size of the input buffer. Use the InputBufferSize property to specify the size of the input buffer. Use the ValuesReceived property to return the total number of values read.