SerialPort.Read Method (Char(), Int32, Int32)


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Reads a number of characters from the SerialPort input buffer and writes them into an array of characters at a given offset.

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

Public Function Read (
	buffer As Char(),
	offset As Integer,
	count As Integer
) As Integer


Type: System.Char()

The character array to write the input to.

Type: System.Int32

The offset in buffer at which to write the characters.

Type: System.Int32

The maximum number of characters to read. Fewer characters are read if count is greater than the number of characters in the input buffer.

Return Value

Type: System.Int32

The number of characters read.

Exception Condition

offset plus count is greater than the length of the buffer.

- or -

count is 1 and there is a surrogate character in the buffer.


The buffer passed is null.


The offset or count parameters are outside a valid region of the buffer being passed. Either offset or count is less than zero.


The specified port is not open.


No characters were available to read.

Use this method for reading characters from the serial 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 characters are available to read. The BytesToRead property can indicate that there are characters to read, but these characters might not be accessible to the stream contained in the BaseStream property because they have been buffered to the SerialPort class.

The Read method does not block other operations when the number of bytes read equals count but there are still unread bytes available on the serial port.

.NET Framework
Available since 2.0
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