SerialPort.ReadExisting Method ()


The .NET API Reference documentation has a new home. Visit the .NET API Browser on to see the new experience.

Reads all immediately available bytes, based on the encoding, in both the stream and the input buffer of the SerialPort object.

Namespace:   System.IO.Ports
Assembly:  System (in System.dll)

public string ReadExisting()

Return Value

Type: System.String

The contents of the stream and the input buffer of the SerialPort object.

Exception Condition

The specified port is not open.

This method returns the contents of the stream and internal buffer of the SerialPort object as a string. This method does not use a time-out. Note that this method can leave trailing lead bytes in the internal buffer, which makes the BytesToRead value greater than zero.

If it is necessary to switch between reading text and reading binary data from the stream, select a protocol that carefully defines the boundary between text and binary data, such as manually reading bytes and decoding the data.


The SerialPort class buffers data, but the stream object contained in the SerialPort.BaseStream property does not. Therefore, the SerialPort object and the stream object might differ on the number of bytes that are available to read. When bytes are buffered to the SerialPort object, the BytesToRead property includes these bytes in its value; however, these bytes might not be accessible to the stream contained in the BaseStream property.

.NET Framework
Available since 2.0
Return to top