Write and Read Data over TCP/IP Interface

Write Data

The write function synchronously writes data to the remote host connected to the tcpclient object. First specify the data, then write the data. The function waits until the specified number of values is written to the remote host.

In this example, a tcpclient object t already exists.

% Create a variable called data
data = 1:10;

% Write the data to the object t
write(t, data)

Note

For any read or write operation, the data type is converted to uint8 for the data transfer. It is then converted back to the data type you set if you specified another data type.

Read Data

The read function synchronously reads data from the remote host connected to the tcpclient object and returns the data. There are three read options:

Read all bytes available (no arguments).
Optionally specify the number of bytes to read.
Optionally specify the data type.

If you do not specify a size, the default read uses the BytesAvailable property value, which is equal to the number of bytes available in the input buffer.

In these examples, a tcpclient object t already exists.

% Read all bytes available.
read(t)

% Specify the number of bytes to read, 5 in this case.
read(t,5)

% Specify the number of bytes to read, 10, and the data type, double.
read(t,10,"double")

Note

For any read or write operation, the data type is converted to uint8 for the data transfer. It is then converted back to the data type you set if you specified another data type.

Acquire Data from Weather Station Server

One of the primary uses of TCP/IP communication is to acquire data from a server. This example shows how to acquire and plot data from a remote weather station.

Note

The IP address in this example is not a working IP address. The example shows how to connect to a remote server. Substitute the address shown here with the IP address or host name of a server you want to communicate with.

Create the tcpclient object using the address shown here and port 1045.

t = tcpclient("172.28.154.231",1045)

t = 
  tcpclient with properties:

              Address: '172.28.154.231'
                 Port: 1045
    NumBytesAvailable: 0

  Show all properties, functions

Acquire data using the read function. Specify the number of bytes to read as 30, for 10 samples from three sensors (temperature, pressure, and humidity). Specify the data type as double.
```
data = read(t,30,"double");
```
Reshape the 1-by-30 data into 10-by-3 data to show one column each for temperature, pressure, and humidity.
```
data = reshape(data,[3,10]);
```
Plot the temperature.
```
subplot(311);
plot(data(:,1));
```
Plot the pressure.
```
subplot(312);
plot(data(:,2));
```
Plot the humidity.
```
subplot(313);
plot(data(:,3));
```
Close the connection between the TCP/IP client object and the remote host by clearing the object.
```
clear t
```

Read Page from Website

In this example, you read a page from the RFC Editor Web site using a TCP/IP object.

Create a TCP/IP object. Port 80 is the standard port for web servers.
```
t = tcpclient("www.rfc-editor.org",80);
```
Set the Terminator property of the TCP/IP object.
```
configureTerminator(t,"LF","CR/LF");
```
You can now communicate with the server using the writeline and readline functions.
To ask a web server to send a web page, use the GET command. You can ask for a text file from the RFC Editor Web site using 'GET (path/filename)'.
```
writeline(t,"GET /rfc/rfc793.txt");
```
The server receives the command and sends back the web page. You can see if any data was sent back by looking at the NumBytesAvailable property of the object.
```
t.NumBytesAvailable
```
Now you can start to read the web page data. By default, readline reads one line at a time. You can read lines of data until the NumBytesAvailable value is 0. Note that you do not see a rendered web page; the HTML file data scrolls by on the screen.
```
while (t.NumBytesAvailable > 0)
    A = readline(t)
end
```
If you want to do more communication, you can continue to read and write data. If you are done with the object, clear it.
```
clear t
```