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SerialPort.ReadLine Method ()


Reads up to the NewLine value in the input buffer.

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

public string ReadLine()

Return Value

Type: System.String

The contents of the input buffer up to the first occurrence of a NewLine value.

Exception Condition

The specified port is not open.


The operation did not complete before the time-out period ended.

- or -

No bytes were read.

Note that while this method does not return the NewLine value, the NewLine value is removed from the input buffer.

By default, the ReadLine method will block until a line is received. If this behavior is undesirable, set the ReadTimeout property to any non-zero value to force the ReadLine method to throw a TimeoutException if a line is not available on the port.

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.


Because the SerialPort class buffers data, and the stream contained in the BaseStream property does not, the two might conflict about how many bytes are available to read. The BytesToRead property can indicate that there are bytes to read, but these bytes might not be accessible to the stream contained in the BaseStream property because they have been buffered to the SerialPort class.

The following code example demonstrates the use of the SerialPort class to allow two users to chat from two separate computers connected by a null modem cable. This code example is part of a larger code example provided for the SerialPort class.

public static void Main()
    string name;
    string message;
    StringComparer stringComparer = StringComparer.OrdinalIgnoreCase;
    Thread readThread = new Thread(Read);

    // Create a new SerialPort object with default settings.
    _serialPort = new SerialPort();

    // Allow the user to set the appropriate properties.
    _serialPort.PortName = SetPortName(_serialPort.PortName);
    _serialPort.BaudRate = SetPortBaudRate(_serialPort.BaudRate);
    _serialPort.Parity = SetPortParity(_serialPort.Parity);
    _serialPort.DataBits = SetPortDataBits(_serialPort.DataBits);
    _serialPort.StopBits = SetPortStopBits(_serialPort.StopBits);
    _serialPort.Handshake = SetPortHandshake(_serialPort.Handshake);

    // Set the read/write timeouts
    _serialPort.ReadTimeout = 500;
    _serialPort.WriteTimeout = 500;

    _continue = true;

    Console.Write("Name: ");
    name = Console.ReadLine();

    Console.WriteLine("Type QUIT to exit");

    while (_continue)
        message = Console.ReadLine();

        if (stringComparer.Equals("quit", message))
            _continue = false;
                String.Format("<{0}>: {1}", name, message));


public static void Read()
    while (_continue)
            string message = _serialPort.ReadLine();
        catch (TimeoutException) { }

.NET Framework
Available since 2.0
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