Start ROS master.

rosinit

Launching ROS Core...
...................Done in 1.3354 seconds.
Initializing ROS master on http://192.168.0.10:52176.
Initializing global node /matlab_global_node_99818 with NodeURI http://bat6315glnxa64:45829/

Create publisher for the '/chatter' topic with the 'std_msgs/String' message type.

chatpub = rospublisher('/chatter','std_msgs/String');

Create a message to send. Specify the Data property.

msg = rosmessage(chatpub);
msg.Data = 'test phrase';

Send the message via the publisher.

send(chatpub,msg);

Shut down the ROS network.

rosshutdown

Shutting down global node /matlab_global_node_99818 with NodeURI http://bat6315glnxa64:45829/
Shutting down ROS master on http://192.168.0.10:52176.
....

You can create an object array to store multiple messages. The array is indexable, similar to any other array. You can modify properties of each object or access specific properties from each element using dot notation.

Create a two - message object array.

msgArray = [rosmessage('std_msgs/String') rosmessage('std_msgs/String')]

msgArray = 
  1x2 ROS String message array with properties:

    MessageType
    Data

Assign data to individual object elements of the array.

msgArray(1).Data = 'Some string'; 
msgArray(2).Data = 'Other string';

Read all the Data properties from the message objects into a cell array.

allData = {msgArray.Data}

allData = 1x2 cell
    {'Some string'}    {'Other string'}

To preallocate an array using ROS messages, use the arrayfun or cellfun functions instead of repmat. These functions properly create object or cell arrays for handle classes.

Preallocate an object array of ROS messages.

msgArray = arrayfun(@(~) rosmessage('std_msgs/String'),zeros(1,50));

Preallocate a cell array of ROS messages.

msgCell = cellfun(@(~) rosmessage('std_msgs/String'),cell(1,50),'UniformOutput',false);