SerialPort.ReadLine Method

Definition

Namespace:

System.IO.Ports

Assembly:

System.IO.Ports.dll

Package:

System.IO.Ports v9.0.0-rc.2.24473.5

Reads up to the NewLine value in the input buffer.

public:
 System::String ^ ReadLine();

public string ReadLine ();

member this.ReadLine : unit -> string

Public Function ReadLine () As String

Returns

String

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

Exceptions

InvalidOperationException

The specified port is not open.

TimeoutException

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

-or-

No bytes were read.

Examples

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 = gcnew Thread(gcnew ThreadStart(PortChat::Read));

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

        _serialPort->Open();
        _continue = true;
        readThread->Start();

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

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

        while (_continue)
        {
            message = Console::ReadLine();

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

        readThread->Join();
        _serialPort->Close();
    }

    static void Read()
    {
        while (_continue)
        {
            try
            {
                String^ message = _serialPort->ReadLine();
                Console::WriteLine(message);
            }
            catch (TimeoutException ^) { }
        }
    }

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;

    _serialPort.Open();
    _continue = true;
    readThread.Start();

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

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

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

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

    readThread.Join();
    _serialPort.Close();
}

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

Public Shared Sub Main()
    Dim name As String
    Dim message As String
    Dim stringComparer__1 As StringComparer = StringComparer.OrdinalIgnoreCase
    Dim readThread As New Thread(AddressOf 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

    _serialPort.Open()
    _continue = True
    readThread.Start()

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

    Console.WriteLine("Type QUIT to exit")

    While _continue
        message = Console.ReadLine()

        If stringComparer__1.Equals("quit", message) Then
            _continue = False
        Else
            _serialPort.WriteLine([String].Format("<{0}>: {1}", name, message))
        End If
    End While

    readThread.Join()
    _serialPort.Close()
End Sub

Public Shared Sub Read()
    While _continue
        Try
            Dim message As String = _serialPort.ReadLine()
            Console.WriteLine(message)
        Catch generatedExceptionName As TimeoutException
        End Try
    End While
End Sub

Remarks

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.

Note

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.