WEBVTT 00:00.050 --> 00:03.680 In this lesson you will write a C plus plus publisher. 00:03.680 --> 00:08.660 We will do the same thing as we did for the Python publisher, but just this time in C plus plus. 00:08.660 --> 00:13.940 So you will be able to compare the code for the same functionalities in the two languages. 00:13.940 --> 00:18.740 Let's go to our workspace again in the source repository. 00:18.740 --> 00:21.290 And then we have our two packages. 00:21.290 --> 00:23.990 I'm going to go to the C plus plus one this time. 00:24.440 --> 00:29.210 And I'm going to go to the source folder of the C plus plus package where we already have. 00:29.240 --> 00:33.560 You can see the first node and also the template for the node. 00:33.560 --> 00:42.590 Let's create a new file named Robot News Station dot CP, which is going to be the node where we have 00:42.590 --> 00:45.380 the publisher and nothing else to do here. 00:45.380 --> 00:51.590 I'm just going to open VSCode and here, so I'm going to close my Python package. 00:51.590 --> 00:53.090 I don't need that anymore. 00:53.090 --> 01:01.020 And let's go to the C plus plus package inside my so Robot news station dot CP I'm going to use the 01:01.020 --> 01:02.040 template. 01:02.610 --> 01:07.260 So I'm just going to take the code from the template and put it there. 01:07.440 --> 01:07.890 Okay. 01:07.920 --> 01:12.300 And as you can see you might have an error just because you need to save the file. 01:12.300 --> 01:13.650 So I'm saving the file. 01:13.650 --> 01:17.220 And after a few seconds you see. 01:17.220 --> 01:20.040 So I had to wait about five 10s. 01:20.490 --> 01:22.890 Then the include is working. 01:22.920 --> 01:23.100 Okay. 01:23.130 --> 01:25.230 So don't worry too much if you have an error. 01:25.260 --> 01:28.770 First save the file first and then let's rename that. 01:28.770 --> 01:34.680 So it's going to be Robot News Station node. 01:34.920 --> 01:35.130 Okay. 01:35.130 --> 01:38.640 So I'm just going to use the same names as I did for Python. 01:38.760 --> 01:42.840 And we also need to modify it here and there. 01:43.950 --> 01:44.160 Okay. 01:44.190 --> 01:48.180 So class name is going to be in three places. 01:48.180 --> 01:54.840 And the node name is going to be here Robot News Station I'm going to use the same. 01:54.840 --> 01:56.820 Let's remove those comments. 01:57.870 --> 02:00.210 And now the node is set up. 02:00.210 --> 02:02.770 So we have to include Lclc-rp. 02:02.920 --> 02:04.150 We create the node. 02:04.150 --> 02:06.850 We have the constructor where we initialize the node. 02:06.850 --> 02:10.330 And then in the main function we start Rosta communications. 02:10.330 --> 02:15.790 We create a shared pointer of the object for robot new station node. 02:15.790 --> 02:18.100 And then we make the node spin and we shut down. 02:18.100 --> 02:20.500 So let's create our publisher. 02:20.500 --> 02:26.800 And in Cplusplus, as you might already know, the syntax is going to be a bit more complicated than 02:26.800 --> 02:27.520 in Python. 02:27.520 --> 02:30.760 There's a bit more stuff to write, but that's just how it is. 02:30.760 --> 02:35.950 So the first thing actually I'm going to do is not to create the publisher, but is to import. 02:35.950 --> 02:38.710 So to include the interface, okay. 02:38.740 --> 02:42.040 And the interface, that's the same one we've used with Python. 02:42.040 --> 02:46.000 So I'm going to use include and I'm going to use the string. 02:46.510 --> 03:00.100 So if I go back here I can do Ros to interface show example interfaces MSG and string okay. 03:00.130 --> 03:03.370 That's the interface I'm going to use, and I can use this in Python. 03:03.370 --> 03:06.010 I can also use this in C plus plus. 03:06.010 --> 03:11.020 And you see this string message has a data field of type string. 03:11.740 --> 03:19.540 So how to include this in C plus plus you will start with example interfaces slash. 03:19.540 --> 03:24.040 And you can see we also have the Autocompletion MSG slash. 03:24.040 --> 03:26.230 And that's going to be string. 03:26.230 --> 03:28.810 So here the string is lowercase okay. 03:28.840 --> 03:32.110 Quite important dot h p p. 03:32.500 --> 03:34.750 We're going to try to import HTTP files. 03:34.750 --> 03:38.440 If you have an error like this you just save the file. 03:39.790 --> 03:42.100 And after a few seconds it's going to be found. 03:42.130 --> 03:45.460 Now because we are using you see we are using our clcp. 03:45.880 --> 03:47.590 So that's one package. 03:47.590 --> 03:50.140 But we are also using example interfaces. 03:50.140 --> 03:52.210 That's a second package. 03:52.210 --> 03:59.890 So we will need to add the dependencies here in the my CPP package I go to the package dot XML. 03:59.890 --> 04:02.650 You see we have a deep end tag with Lclc-rp. 04:02.980 --> 04:07.690 I'm going to add another one depend example. 04:09.700 --> 04:13.960 Interfaces and I close the depend tag. 04:13.990 --> 04:14.380 All right. 04:14.380 --> 04:16.960 So that's the same thing as we did for Python. 04:16.960 --> 04:22.750 But now in Cplusplus there is an additional thing you need to do because you're going to compile the 04:22.750 --> 04:23.740 file okay. 04:23.770 --> 04:25.390 And you need the dependency. 04:25.390 --> 04:28.390 When you compile you need to link the dependencies. 04:28.390 --> 04:31.540 So we need to add something in the CMake list.txt. 04:31.570 --> 04:33.040 Here we find the dependencies. 04:33.040 --> 04:37.000 You see we have first element cmake and we have lclc-rp. 04:37.180 --> 04:46.630 You're going to add another find package with example interfaces. 04:46.630 --> 04:50.710 And we've also required okay. 04:50.740 --> 04:57.340 And then we're going to use that also when we link the dependencies here with the executable. 04:57.370 --> 04:57.700 All right. 04:57.700 --> 05:04.740 So if you add a new package cage inside the file, you add it to the package dot XML and also to the 05:04.740 --> 05:06.420 Cmakelists.txt. 05:07.260 --> 05:07.560 Great. 05:07.590 --> 05:10.500 Now we have included the interface. 05:10.500 --> 05:12.450 Let's create the publisher. 05:12.450 --> 05:15.330 We are going to create a private attribute. 05:15.330 --> 05:17.490 So we have the public and the private. 05:17.490 --> 05:23.790 In the private attribute I'm going to create a publisher and the publisher is going to be RCL, cpp 05:24.960 --> 05:30.630 and inside RCL cpp we have a publisher class okay. 05:30.660 --> 05:33.510 And this publisher class we need to give. 05:33.510 --> 05:35.850 So this is going to be a template. 05:35.850 --> 05:38.520 We need to give the interface. 05:38.520 --> 05:48.900 So the interface is example interfaces and then MSG and then string just like that okay. 05:48.930 --> 05:54.240 So when you create a publisher here when you declare a publisher you have to provide also the type in 05:54.240 --> 05:56.790 C plus plus here using those brackets. 05:56.790 --> 05:57.900 So that's a template. 05:57.900 --> 06:04.920 And we are not actually going to create just a publisher, we are going to create a shared pointer to 06:04.950 --> 06:05.820 a publisher. 06:05.850 --> 06:06.120 Okay. 06:06.150 --> 06:11.520 So once again we use shared pointer for everything in C plus plus in rust. 06:11.520 --> 06:14.460 And this shared pointer here this sharedptr. 06:14.490 --> 06:19.680 As you can see this is going to create an STD shared pointer here. 06:19.710 --> 06:19.980 Okay. 06:20.010 --> 06:23.400 So that's something you can use to simplify your code. 06:23.460 --> 06:26.640 And let's call it publisher. 06:27.720 --> 06:27.900 Okay. 06:27.930 --> 06:34.410 So that's the name we give it with an underscore here just to say that that's an attribute of the class. 06:34.440 --> 06:34.860 Great. 06:34.860 --> 06:40.110 So now that I have declared it here I can initialize it in my constructor. 06:40.110 --> 06:46.200 So publisher publisher like that is equal to. 06:46.320 --> 06:48.390 And then I'm going to use this. 06:48.420 --> 06:48.570 Okay. 06:48.600 --> 06:55.230 It's not mandatory but it's just to explicitly say that I'm using the node functionality. 06:55.230 --> 06:56.220 So you don't need to do that. 06:56.220 --> 07:02.670 But as I told you before, I'm going to do this in this course and create a publisher. 07:02.670 --> 07:06.990 So you have a create publisher method here to create a publisher. 07:07.020 --> 07:09.840 And that's going to return a shared pointer to a publisher. 07:09.840 --> 07:12.540 You need to give the interface once again. 07:12.540 --> 07:18.960 So example interfaces msg and then string. 07:18.960 --> 07:21.120 And then you're going to open the parentheses. 07:21.120 --> 07:25.140 And you need to give the name of the topic. 07:25.140 --> 07:27.480 So we've already provided the interface. 07:27.480 --> 07:29.820 So the data type like this. 07:29.820 --> 07:31.290 Then we need to give the name. 07:31.290 --> 07:35.220 Let's also name it Robot News okay. 07:35.220 --> 07:41.280 And also in those parentheses we are going to provide the queue size of ten okay. 07:41.280 --> 07:47.970 So this I already explained with Python it's just a buffer in case you have too many messages are too 07:47.970 --> 07:54.600 big or it's a lossy network, then that's going to add messages to a buffer up to ten messages okay. 07:54.630 --> 07:56.580 And with that we have created the publisher. 07:56.610 --> 07:59.850 Now let's create a method to publish. 07:59.870 --> 08:04.070 So I'm going to add a method in private here void. 08:04.070 --> 08:05.780 We don't return anything. 08:05.780 --> 08:08.090 Publish news okay. 08:08.090 --> 08:09.530 Let's call it publish news. 08:10.040 --> 08:12.800 And I'm going to put this function as private. 08:12.800 --> 08:15.920 Because this is not something we call from outside of the class. 08:15.920 --> 08:18.590 We're just going to use it from a timer okay. 08:18.620 --> 08:20.150 And the timer is inside the class. 08:20.150 --> 08:22.490 So that's why I put it here in private. 08:22.490 --> 08:23.480 And let's create. 08:23.510 --> 08:27.590 We need to create a message I'm going to use the auto type. 08:27.710 --> 08:35.270 So auto MSG and the message is example interfaces msg string. 08:35.270 --> 08:41.270 You can really see here the powerfulness of the auto completion okay I really don't recommend you to 08:41.300 --> 08:45.260 write C plus plus code for Ros2 without auto completion okay. 08:45.290 --> 08:47.210 Because that's going to become a nightmare. 08:47.300 --> 08:50.780 So you create here a string object. 08:50.780 --> 08:52.940 And actually here is kind of an exception. 08:52.940 --> 08:54.770 It's not going to be a shared pointer. 08:54.770 --> 08:57.860 It's just going to be the object directly okay. 08:57.860 --> 09:00.470 So then we can do MSG dot. 09:00.470 --> 09:05.630 And here we have a field named data that can be high. 09:05.930 --> 09:08.360 This is okay. 09:08.360 --> 09:11.630 And let's directly do the string construction. 09:11.660 --> 09:14.210 Let's create a robot name. 09:14.210 --> 09:25.280 So I'm going to do this here STD string robot name like that. 09:25.640 --> 09:28.880 And let's initialize the robot name here. 09:30.020 --> 09:36.710 Robot name to um, let's name it this time R2d2. 09:37.190 --> 09:38.000 All right. 09:38.000 --> 09:41.720 And I'm going to concatenate that robot name. 09:41.720 --> 09:45.020 And actually just in case we get some errors. 09:45.020 --> 09:49.130 So this is an STD string that is not an STD string. 09:49.130 --> 10:01.190 So I'm going to do STD string of this text plus this string plus. 10:01.310 --> 10:05.480 STD string of that text. 10:05.480 --> 10:13.310 So hi, this is robot name from the robot news station. 10:14.270 --> 10:15.650 Um, STD here. 10:16.820 --> 10:20.930 Okay, so we create the object for the message. 10:20.930 --> 10:25.790 We here we add a data field because we have a data inside the interface. 10:25.790 --> 10:27.260 And then we just need to publish. 10:27.260 --> 10:28.430 So we have the publisher. 10:28.430 --> 10:30.320 We do simply publisher. 10:31.160 --> 10:34.670 So publisher the publisher is a shared pointer. 10:34.670 --> 10:38.240 So that's an arrow publish. 10:38.420 --> 10:39.710 And what do we publish. 10:39.710 --> 10:43.970 We publish the message as simple as that. 10:43.970 --> 10:50.330 And now that we have a publisher and a method to publish, well we need to actually call that method. 10:50.330 --> 10:52.520 And we want to publish twice per second. 10:52.520 --> 10:54.710 So I'm going to add a timer. 10:54.710 --> 10:56.360 So I'm going to create a timer here. 10:56.360 --> 11:03.070 For example here our Clcp Timer base. 11:03.700 --> 11:08.350 And also no surprise, still a shared pointer. 11:09.430 --> 11:13.690 Okay, so this we've done it already in the section on nodes for this course. 11:13.690 --> 11:17.530 And after the publisher I'm going to initialize my timer. 11:18.820 --> 11:21.670 Timer is equal to this. 11:22.240 --> 11:30.250 So once again this is not mandatory just for me to explicitly say I'm using the node class create wall 11:30.280 --> 11:30.790 timer. 11:30.790 --> 11:33.100 So in C plus plus it's called wall timer. 11:33.100 --> 11:35.830 And we need to give a duration. 11:35.830 --> 11:43.300 So what I'm going to do here instead of doing STD Chrono and duration I'm gonna make things a bit simpler. 11:43.300 --> 11:52.150 I'm going to do using namespace std chrono literals. 11:52.150 --> 11:58.480 So by doing using namespace std chrono literals at the beginning, then I can just give a literal for 11:58.480 --> 12:03.730 example 0.5 s for second and that's going to be recognized. 12:03.760 --> 12:03.970 Okay. 12:04.000 --> 12:07.720 We don't need to write the whole STD, Chrono etc.. 12:07.750 --> 12:12.400 So I have first the period in in second here. 12:12.400 --> 12:14.860 And then I need to provide the callback. 12:14.860 --> 12:19.120 So to provide the callback I need to do std bind. 12:19.420 --> 12:24.580 And we will first provide the reference to. 12:24.670 --> 12:28.750 So to this which is robot new station publish news. 12:28.750 --> 12:38.020 So robot news station node publish news with no parentheses. 12:38.020 --> 12:48.400 And then comma this specify that is this object we are binding to and a semicolon here. 12:48.430 --> 12:49.060 All right. 12:49.060 --> 12:54.220 So if this syntax is still complicated for you well don't worry because as I told you before it's always 12:54.220 --> 12:55.150 going to be the same thing. 12:55.150 --> 12:58.030 So after a few repetitions you will get used to it. 12:58.390 --> 12:59.500 And that's going to be it. 12:59.500 --> 13:05.060 I'm going to add a log here just to finish the constructor as Clcp info. 13:05.090 --> 13:09.650 With this get logger. 13:10.640 --> 13:18.950 And just to say the robot news station has been started. 13:19.130 --> 13:19.340 Okay. 13:19.340 --> 13:23.210 Just a log to finish the constructor. 13:23.240 --> 13:24.020 Okay. 13:24.020 --> 13:26.930 And now we can so we can save the file. 13:26.960 --> 13:28.370 Make sure you save the file. 13:28.370 --> 13:32.690 And let's go to the Cmakelists.txt to create an executable. 13:32.720 --> 13:34.460 We have the first one here. 13:34.460 --> 13:36.890 So let's add a new line here. 13:36.890 --> 13:39.500 Add executable. 13:39.650 --> 13:40.970 What's going to be the name. 13:40.970 --> 13:44.900 Let's name it Robot News Station. 13:44.900 --> 13:52.220 So once again I use the same name for the executable for the file name and for the node name. 13:53.360 --> 13:56.570 So robot new station where is the file. 13:56.570 --> 14:02.970 The file is in src Slash and then robot news station WKRP. 14:03.000 --> 14:06.330 Robot news station dot CPP. 14:07.170 --> 14:09.180 After that, I will do payment. 14:09.720 --> 14:17.190 Target dependencies I will first provide the name of the executable, which is Robot News Station. 14:17.190 --> 14:19.410 That's the name here I've provided here. 14:19.440 --> 14:25.260 You see, this is where you should start not to make confusions because that's the name of the executable. 14:25.290 --> 14:28.860 Here was obvious cpp node was that name. 14:28.860 --> 14:32.370 It's not the name of the file, it's not the name of the node inside the file. 14:32.370 --> 14:35.940 This is the name of the executable you write here. 14:35.970 --> 14:38.100 Okay so not to be confused. 14:38.130 --> 14:41.130 And then we need to provide all the dependencies. 14:41.130 --> 14:42.750 We need to link to that. 14:42.750 --> 14:45.240 So we have our clcp of course. 14:46.620 --> 14:49.200 But then if we look at the file we have our clcp. 14:49.200 --> 14:52.680 And we also have example interfaces. 14:52.680 --> 15:02.430 So I'm going to write example interfaces that we have also Uh, added here we find package. 15:02.460 --> 15:02.970 Okay. 15:03.000 --> 15:06.900 So important that you add this line and that you add the dependency here. 15:06.990 --> 15:09.540 Then this is going to create an executable. 15:09.540 --> 15:11.460 But we also need to install it. 15:11.460 --> 15:14.880 So I'm going to add simply one more line here. 15:15.210 --> 15:17.370 Robot news station. 15:17.790 --> 15:18.060 Okay. 15:18.090 --> 15:20.100 So one executable per line. 15:20.100 --> 15:22.080 And you don't need to change this structure. 15:22.080 --> 15:22.860 And that's it. 15:22.860 --> 15:28.770 So you can see after you've created your first executable adding another one is not going to take that 15:28.770 --> 15:29.460 much time. 15:29.460 --> 15:34.110 Let's save the file and we should be able to compile. 15:34.110 --> 15:40.650 So let's go back to the terminal I go to my roster workspace and I do call on build. 15:41.820 --> 15:44.460 I'm just going to build the package. 15:44.460 --> 15:48.960 So the C plus plus one with packages select. 15:50.760 --> 15:53.130 So my CP pkg. 15:56.400 --> 15:56.940 Okay. 15:56.940 --> 16:05.490 So it has been built and now I could so I could source, install, setup bash, run it from here. 16:05.670 --> 16:09.960 I can also just open a new terminal is going to be the same. 16:10.200 --> 16:17.790 So let's do that and let's run Ros to run my CP pg with. 16:17.820 --> 16:19.920 So just in case I press tab twice. 16:20.040 --> 16:23.160 And you see I have my new executable here. 16:23.190 --> 16:25.440 Robot news station. 16:26.790 --> 16:29.100 And we have the robot new station has been started. 16:29.100 --> 16:30.240 So we have the log. 16:30.630 --> 16:32.730 And you see the node is hanging. 16:32.730 --> 16:34.710 So the node is spinning. 16:34.710 --> 16:39.150 And we can also do Ros to node list. 16:39.720 --> 16:40.350 Okay. 16:40.380 --> 16:45.000 Ros to node info with that name. 16:46.530 --> 16:46.830 Okay. 16:46.860 --> 16:54.060 We see we have a publisher which is Robot News and the type is string from example interfaces package. 16:54.060 --> 16:56.610 So we can find all this information again. 16:56.610 --> 17:02.300 And we can also do Ros two to topic eco robot news. 17:06.470 --> 17:10.940 And you see how this is out to the two from the robot news station. 17:10.940 --> 17:18.200 And this is actually something else we can do is we can start the subscriber node from. 17:18.200 --> 17:24.830 So Rostron my Python package with a smartphone okay. 17:24.860 --> 17:27.680 So we are running the C plus plus publisher. 17:27.680 --> 17:33.320 And here I'm going to try to run the subscriber I have created with Python for the exact same topic. 17:33.320 --> 17:36.770 So with the same name and same data type let's see what happens. 17:38.540 --> 17:40.100 And it correctly works. 17:40.100 --> 17:45.980 You see we receive the data from the C plus plus publisher. 17:45.980 --> 17:51.050 And so with this example you can clearly see that Ros two is language agnostic. 17:51.080 --> 17:55.520 You can create one node in C plus plus and one other node in Python. 17:55.520 --> 17:59.990 And both nodes can communicate using for example, topics.