WEBVTT 00:00.080 --> 00:05.840 And now that we have a Cplusplus publisher, let's write a Cplusplus subscriber. 00:05.840 --> 00:10.520 We are going to write a node for our smartphone like also we did with Python. 00:10.520 --> 00:15.710 And in this node we're going to create a subscriber for the topic we have just published to in the last 00:15.710 --> 00:16.280 lesson. 00:16.280 --> 00:24.470 So let's go again to our C plus plus package inside the source folder. 00:24.470 --> 00:30.410 And let's create a new file smartphone dot cp okay then. 00:30.410 --> 00:31.490 So I have this file. 00:31.490 --> 00:37.430 I'm going to open VSCode again from the source folder of the workspace. 00:37.550 --> 00:42.290 And well I've already had those robot new station here. 00:42.290 --> 00:44.390 And I have my smartphone CP. 00:44.690 --> 00:47.990 So I will once again start with the template. 00:47.990 --> 00:58.100 I will take the code from the template and put it here in the smartphone that CP, I will just do smartphone 00:58.100 --> 01:03.090 node and replace here. 01:03.120 --> 01:07.350 Plus, change the node name to smartphone. 01:07.500 --> 01:09.360 Okay, let's keep things simple. 01:09.360 --> 01:13.080 And once again I use the same name for the file name and the node name. 01:13.200 --> 01:15.600 Let's remove those comments. 01:16.680 --> 01:20.010 And I'm going to save as well. 01:20.490 --> 01:20.760 Okay. 01:20.790 --> 01:25.320 So we can have the dependency here that's found. 01:25.800 --> 01:26.160 Okay. 01:26.160 --> 01:28.290 So the node is initialized. 01:28.290 --> 01:30.510 You can see now it's going very quick. 01:30.510 --> 01:32.520 And let's create a subscriber. 01:32.520 --> 01:37.290 And actually before we create the subscriber I'm going to include the interface. 01:37.290 --> 01:38.910 So what interface. 01:38.910 --> 01:44.160 Well in this case if you have a subscriber and you already know that you have a publisher to a topic, 01:44.190 --> 01:46.350 then you need to make sure you use the same interface. 01:46.350 --> 01:47.940 So we don't even have a choice. 01:47.940 --> 01:52.800 We're going to use this example interfaces msg string. 01:53.100 --> 02:00.810 So we include it here include example Interfaces. 02:01.170 --> 02:04.770 MSG string dot http. 02:05.340 --> 02:09.510 Exact same thing and I save the file. 02:09.660 --> 02:11.310 Wait a few seconds. 02:12.090 --> 02:12.540 Okay. 02:12.570 --> 02:18.150 And then as we add these example interfaces, we should also make sure that it's in the package dot 02:18.150 --> 02:18.810 XML. 02:18.930 --> 02:23.760 It's already here and in the cmakelists.txt it's already there. 02:23.760 --> 02:26.280 So nothing else to do. 02:26.310 --> 02:28.410 Now for the subscriber. 02:28.410 --> 02:30.360 So we're going to create a subscriber. 02:30.360 --> 02:34.380 We're going to declare it here in as a private attribute. 02:34.380 --> 02:37.020 Then we're going to initialize it in the constructor. 02:37.020 --> 02:41.610 And then we're going to create a callback so that we can receive the messages. 02:41.640 --> 02:44.010 And actually I'm just going to start with the callback. 02:44.040 --> 02:44.520 Okay. 02:44.520 --> 02:50.130 So in private I'm going to use the callback because this is something that's only going to be called 02:50.190 --> 02:52.110 by the node itself. 02:52.110 --> 02:52.800 When we spin. 02:52.800 --> 02:55.410 We don't really want to call that from the outside. 02:55.410 --> 02:57.810 So that's going to be in private. 02:57.870 --> 02:59.230 It's going to be void. 02:59.260 --> 03:00.910 It's not returning anything. 03:00.910 --> 03:05.410 And let's name it Callback Robot news. 03:05.410 --> 03:12.850 So once again, I like to use the callback name to start the function with callback, and then put the 03:12.850 --> 03:14.080 name of the topic. 03:14.080 --> 03:16.480 And what do we receive here? 03:16.480 --> 03:21.100 We're going to receive the message, but actually we are not going to receive the message. 03:21.100 --> 03:27.610 We are going to receive a shared pointer to the message and even better, a const shared pointer. 03:27.610 --> 03:28.900 So that's going to be const. 03:28.900 --> 03:30.130 And then the type. 03:30.130 --> 03:36.850 So example interfaces msg string. 03:36.850 --> 03:38.620 Here we string with uppercase. 03:38.920 --> 03:41.380 And then we have also shared pointer. 03:41.380 --> 03:49.540 So for all the interfaces in Ros2 you can also use this Sharedptr to make it a shared pointer. 03:49.720 --> 03:51.520 And let's call it msg. 03:51.880 --> 03:53.710 That's the message we receive. 03:54.820 --> 03:55.180 All right. 03:55.180 --> 04:01.480 So you see const the type with a short pointer and then the name that you that you choose, and then 04:01.480 --> 04:02.830 you can do whatever you want. 04:02.860 --> 04:08.260 So here we are just going to print it as Clcp info. 04:08.290 --> 04:16.030 With this get logger and let's do that. 04:16.030 --> 04:18.610 Let's print a string. 04:18.790 --> 04:20.590 And what do we print. 04:20.620 --> 04:22.060 Not just the message. 04:22.060 --> 04:23.830 The message is an object. 04:23.830 --> 04:25.540 So we're going to use. 04:25.570 --> 04:29.710 And we're going to use an arrow because it's a shared pointer to the object. 04:29.710 --> 04:34.420 So message arrow data we want to print the data. 04:34.420 --> 04:37.600 And data is an STD string. 04:37.600 --> 04:44.890 So to make it work with Lclc-rp info we're going to cast it to a C string. 04:44.890 --> 04:52.930 So you can just do dot c str with the parentheses to make it work with this percentage s. 04:52.960 --> 04:53.470 All right. 04:53.470 --> 04:54.460 And we have the callback. 04:54.460 --> 05:01.700 So now that we have the callback let's create the subscriber I'm going to add here as a private attribute. 05:01.730 --> 05:06.080 I'll Klccp subscriber. 05:06.080 --> 05:09.350 So it's not subscriber it's subscription. 05:09.350 --> 05:12.350 So we have a subscription object we need to provide. 05:12.350 --> 05:16.820 So as we did here you see with the publisher we also need to provide. 05:16.820 --> 05:17.840 So that's going to be a template. 05:17.840 --> 05:21.110 And we need to provide the interface. 05:21.110 --> 05:28.310 So I'm going to write the interface example interfaces MSG string. 05:28.670 --> 05:34.250 And of course maybe you have already guessed it's not just going to be a subscription object, it's 05:34.250 --> 05:38.330 going to be a shared pointer to the subscription object. 05:38.330 --> 05:43.490 And let's name it subscriber subscriber. 05:44.540 --> 05:47.060 So you could call it subscription subscriber. 05:47.090 --> 05:49.220 It doesn't really matter. 05:49.220 --> 05:54.320 Usually we talk about publishers and subscribers, but in the code it's subscription. 05:54.320 --> 05:57.140 So we have that declaration here. 05:57.140 --> 05:58.670 Let's initialize. 05:58.700 --> 06:08.960 Subscriber is equal to and I'm using this just to explicitly say we're using the Clcp node class and 06:08.960 --> 06:12.350 create subscription. 06:12.350 --> 06:21.500 We need to pass again the type for example interfaces msg string. 06:21.500 --> 06:23.420 And then I'm going to open the parentheses. 06:23.420 --> 06:25.580 And what do we need to provide. 06:25.610 --> 06:28.790 We need to provide first the name. 06:28.790 --> 06:30.740 So we've already provided the type. 06:30.980 --> 06:32.930 So no need to provide inside the parentheses. 06:32.930 --> 06:33.980 It's already here. 06:34.010 --> 06:35.480 The name is going to be. 06:35.510 --> 06:36.860 And that's very important. 06:36.860 --> 06:41.660 If we want the publisher and the subscriber to communicate we need to use the same name. 06:41.660 --> 06:45.290 So robot news just like that. 06:45.290 --> 06:46.790 Then we have the queue size. 06:46.790 --> 06:48.650 So I'm just going to use ten. 06:48.650 --> 06:52.310 And just after the queue size we have the callback. 06:52.310 --> 06:55.040 So maybe I'm going to go back to a new line here. 06:55.470 --> 06:58.350 and also here because it's going to be quite long. 06:58.350 --> 07:05.490 So to provide the callback we use once again std bind with first the reference. 07:05.490 --> 07:13.080 So that's going to be smartphone node callback robot news okay. 07:13.110 --> 07:17.910 So reference to the method without parentheses. 07:18.240 --> 07:21.540 Then we have a comma. 07:21.930 --> 07:26.370 It's going to be this to say that we bind to this node. 07:26.370 --> 07:28.560 And then that's not it. 07:28.680 --> 07:29.580 Why is that. 07:29.580 --> 07:32.010 Because we have here a parameter. 07:32.010 --> 07:35.940 So if you just try to run it like this and compile, it's not going to work. 07:35.970 --> 07:40.320 You need to add an what's called an STD placeholder. 07:40.320 --> 07:44.250 So STD placeholders. 07:45.000 --> 07:52.470 So it's just something you need to write and then underscore one because you have one argument okay. 07:52.500 --> 08:02.250 If you had two arguments you will need to add another one std placeholder with so STD placeholders underscore 08:02.280 --> 08:04.350 two and then three, etc.. 08:04.380 --> 08:09.690 Okay, to make things a bit simpler here, I'm going to sew at the top. 08:09.690 --> 08:16.110 I'm going to do using namespace std placeholders. 08:16.140 --> 08:16.650 Okay. 08:16.650 --> 08:20.670 So then I can just write underscore one here. 08:20.670 --> 08:23.520 And let's not forget the semicolon at the end. 08:23.550 --> 08:23.790 Okay. 08:23.820 --> 08:26.460 So to recap here you do create subscription. 08:26.460 --> 08:29.790 You provide the interface here between brackets. 08:29.790 --> 08:31.350 Then you open the parentheses. 08:31.350 --> 08:37.830 You put first argument is the name, then queue size and then stdbind with first the reference to the 08:37.830 --> 08:39.270 function this. 08:39.270 --> 08:42.840 So the keyword this and then a placeholder. 08:42.840 --> 08:47.730 That's going to be for that argument that we have in the function. 08:47.730 --> 08:50.730 And let's finish with our clcp. 08:50.730 --> 08:53.400 So now that's done let's finish the constructor. 08:54.190 --> 09:06.070 our club info this get logger and let's just say smartphone has been studied. 09:06.430 --> 09:07.240 Okay. 09:07.240 --> 09:13.630 Just so we have something that's printed on the screen and that's it for the subscriber code. 09:13.660 --> 09:13.810 Okay. 09:13.840 --> 09:19.240 So you create a shared pointer here, you declare it, you create it here in the constructor. 09:19.240 --> 09:22.600 And then you have a callback better as a private method here. 09:22.600 --> 09:25.330 And you receive the message as a shared pointer. 09:25.330 --> 09:27.190 And then you can just do whatever you want. 09:27.190 --> 09:28.420 Here we just print it. 09:28.420 --> 09:31.240 So let's you make sure you save everything. 09:31.240 --> 09:36.010 Now you go back to the Cmakelists.txt and we are going to add a new executable. 09:36.040 --> 09:37.990 Add executable. 09:37.990 --> 09:40.870 Let's call it smartphone. 09:40.900 --> 09:43.000 It's going to be the name of the executable. 09:43.000 --> 09:44.560 Where is the file. 09:44.740 --> 09:58.600 The file is in source smartphone dot CVP smartphone dot cpp Then payment target dependencies with the 09:58.600 --> 10:00.040 executable name. 10:00.040 --> 10:02.050 Smart phone. 10:02.080 --> 10:04.360 What do we need to link? 10:04.660 --> 10:09.580 We need to link our Clcp and example interfaces. 10:09.610 --> 10:12.550 If you are not sure you go back you see what do we include? 10:12.730 --> 10:15.730 We include that one and we include that one. 10:16.420 --> 10:18.100 That's it for the executable. 10:18.190 --> 10:22.390 We just add the executable to the targets to install. 10:23.140 --> 10:28.330 So that's going to be smart phone and that's it. 10:28.330 --> 10:30.310 So one executable per line. 10:30.310 --> 10:32.830 And you don't add any comma or anything here. 10:32.860 --> 10:33.400 Okay. 10:33.400 --> 10:34.510 Let's save. 10:34.510 --> 10:39.940 And then we can go back and let's just go to our roster workspace. 10:39.940 --> 10:50.680 And let's do a call on build with packages select and my CP package. 10:53.450 --> 10:56.420 Okay, so you can see it took 19 seconds for me. 10:56.750 --> 10:59.060 Um, let's open a new terminal. 10:59.060 --> 11:00.920 Just so we have everything sourced. 11:00.920 --> 11:04.730 I'm going to also split it in two and we can start. 11:04.730 --> 11:06.950 I'm going to start it here plus two. 11:06.980 --> 11:11.960 Run my CP pkg and that's going to be smart. 11:11.990 --> 11:14.270 Should be found smart phone. 11:14.750 --> 11:15.920 Let's press enter. 11:15.920 --> 11:23.000 And you see smartphone has been started I can do Ros two node list okay. 11:23.030 --> 11:28.580 Smart phone I can do Ros two node info with a smart phone. 11:29.510 --> 11:31.670 You can see that in the. 11:31.700 --> 11:35.150 So this time in the subscribers we have robot news okay. 11:35.180 --> 11:38.570 So for the publishers it was in the in the publishers here. 11:38.720 --> 11:40.490 Here we have a subscriber. 11:40.490 --> 11:43.490 So the smartphone is a subscriber to the Robot News. 11:43.490 --> 11:45.980 And let's test the full communication. 11:45.980 --> 11:53.090 So Ros to run my CP pkg with We've robot news station. 11:54.020 --> 11:54.590 You see that? 11:54.590 --> 11:56.120 We received the messages. 11:56.600 --> 11:58.520 Now I'm going to stop that one. 11:58.520 --> 12:03.440 And let's start to run my pi pg. 12:04.580 --> 12:06.110 Let's start the Python one. 12:07.670 --> 12:09.830 And you can see that we also receive. 12:09.860 --> 12:11.360 And the message is different. 12:11.360 --> 12:12.890 You see the robot name is different. 12:12.890 --> 12:14.210 So I'm going to stop that one. 12:14.420 --> 12:17.480 You see the the robot name is different. 12:17.510 --> 12:20.750 We receive messages from two different publishers. 12:20.750 --> 12:22.340 But because both publishers. 12:22.340 --> 12:27.290 So the C plus Plus one and the Python one were publishing to the same topic with the same data type, 12:27.290 --> 12:30.260 then we receive all the messages in the subscriber. 12:30.260 --> 12:33.170 We don't even know from who we receive the messages. 12:33.170 --> 12:34.970 It doesn't matter at all, okay? 12:35.000 --> 12:41.090 We just receive messages that correspond to the string data type on the robot news topic. 12:41.090 --> 12:47.750 So now what you can try is you can run any combination of Python or C plus plus publisher with any other 12:47.750 --> 12:51.200 combination of Python or C plus plus subscriber.