WEBVTT 00:00.080 --> 00:03.950 And let's now improve this node with object oriented programming. 00:03.950 --> 00:07.340 Just as for Python, we're going to improve this. 00:07.340 --> 00:12.380 And then that's going to be the C plus plus template you can use for any future node that you create. 00:12.380 --> 00:18.650 So instead of creating the node here using the node class directly from the main, I'm going to create 00:18.650 --> 00:24.230 my own class for the node that's going to inherit from our Clcp node. 00:24.230 --> 00:28.790 And then in this class I will be able to add as many functionalities as I want. 00:28.820 --> 00:31.370 That's going to make it much easier for the future. 00:31.370 --> 00:35.030 So let's create a C plus plus class class. 00:35.120 --> 00:41.510 Let's call it my node and then how to inherit from Clcp node. 00:41.510 --> 00:43.160 I'm going to do this public. 00:43.160 --> 00:48.920 So that's the public inheritance Clcp node. 00:49.370 --> 00:52.310 That's the declaration of the class. 00:52.310 --> 00:53.960 So I add curly brackets. 00:53.960 --> 01:00.290 And one very important thing is don't forget the semicolon at the end of this curly bracket here okay. 01:00.290 --> 01:05.650 And in this I will have public and then private in public. 01:05.650 --> 01:08.590 I'm going to add the class constructor. 01:08.590 --> 01:11.350 So my node like that. 01:11.350 --> 01:20.290 And we can directly use the node constructor here and pass the node name okay. 01:21.310 --> 01:26.080 So this syntax will if you don't know much about this syntax that's basically how to create a class 01:26.080 --> 01:26.530 in C plus. 01:26.530 --> 01:31.630 Plus you can find also other tutorials if you feel too lost about this. 01:31.630 --> 01:36.550 But be reassured that once we have finished this, we can use this as a template. 01:36.550 --> 01:39.700 And then well, after you get used to it, it's going to be much easier. 01:39.760 --> 01:44.290 So let's open the curly brackets for the function. 01:44.290 --> 01:50.740 And that's basically it for our first class, our first node class okay. 01:50.770 --> 01:53.950 So we need to inherit from our sleep node. 01:53.950 --> 01:57.010 And then we need to call the parent constructor. 01:57.040 --> 01:58.270 That's what we do here. 01:58.270 --> 02:03.750 So my node we call the parent constructor and we need to give it also the node name. 02:03.750 --> 02:05.970 That's basically what we've done here. 02:05.970 --> 02:09.570 Then if we want to add a functionality here, that's what we've done. 02:09.570 --> 02:12.030 We can use Lclc-rp info. 02:12.150 --> 02:16.110 So Lclc-rp info. 02:16.500 --> 02:23.520 And then as we add directly in the class that is a node because of the inheritance, we don't need to 02:23.550 --> 02:24.420 do node something. 02:24.420 --> 02:27.120 We can just do get logger. 02:27.420 --> 02:27.780 Okay. 02:27.810 --> 02:28.830 Just like that. 02:28.830 --> 02:36.000 And usually what I like to do when I use the functionalities from the class here from the node, just 02:36.000 --> 02:39.180 to make it explicit, I use the this keyword. 02:39.180 --> 02:45.840 So you don't need to do you don't need to write this okay, I'm going to use this here for this course, 02:45.870 --> 02:50.250 just so that when you see a function you know that it's coming actually from the node class, but it's 02:50.250 --> 02:52.140 not mandatory, all right? 02:52.170 --> 02:54.750 It's just a kind of a convention I will follow here. 02:54.750 --> 02:56.430 And then you can do whatever you want. 02:56.430 --> 03:05.650 So we first have the logger and then we have the string, which I'm going to just take from here, and 03:05.650 --> 03:07.210 that's basically the same thing. 03:07.510 --> 03:08.800 So we have a constructor. 03:08.800 --> 03:11.620 In the constructor we print something. 03:11.620 --> 03:14.770 So now what I can do I'm just going to remove that line. 03:15.040 --> 03:23.590 And I'm going to modify this line so that instead of creating just a clcp node I'm still going to do 03:23.620 --> 03:25.000 a shared pointer. 03:25.000 --> 03:29.800 But this time it's going to be my node okay. 03:29.830 --> 03:31.270 And open close parentheses. 03:31.300 --> 03:35.110 We don't have anything to pass here because we don't have any parameter. 03:35.110 --> 03:42.190 So what we do is we create a shared pointer of a new object from my node that inherits from node. 03:42.190 --> 03:44.770 And then we can just spin the node. 03:44.770 --> 03:46.630 You can see the auto here. 03:46.660 --> 03:48.910 It's a shared pointer to my node. 03:48.910 --> 03:51.280 And my node is an lltp node. 03:51.280 --> 03:52.330 So that's the same thing. 03:52.330 --> 03:52.750 Great. 03:52.750 --> 03:54.490 And that is basically the template. 03:54.520 --> 03:58.000 So the template you don't need this line here. 03:58.030 --> 04:00.420 That's the template I'm going to give to you. 04:00.420 --> 04:03.660 So those 20 lines here, you include the lcbp. 04:03.690 --> 04:08.370 You create the class and then you have the main where you initialize the rows to communication. 04:08.370 --> 04:11.400 You create a node, you make the node spin and then you shut down. 04:11.430 --> 04:11.910 Okay. 04:11.940 --> 04:15.300 Now let's come back to this code. 04:15.300 --> 04:20.700 And I'm just going to add like I did with Python, I'm going to add one more functionality which is 04:20.700 --> 04:21.840 a timer okay. 04:21.870 --> 04:27.990 Because the timer is going to be super useful if you want to have a node that repeats an action, let's 04:27.990 --> 04:30.780 say ten times per second or 20 times per second. 04:30.780 --> 04:35.400 So it could be a sensor reading some data, it could be a controller or it could be anything. 04:35.400 --> 04:39.840 And that's very frequent to use this kind of structure in robotics. 04:39.840 --> 04:43.200 So we're going to see how to create a timer. 04:43.200 --> 04:48.900 And the syntax of course with C plus plus is always a bit more complicated than Python. 04:48.900 --> 04:55.530 So first of all I will create here an so private attribute or clcp. 04:56.430 --> 05:00.170 And we have Timer base. 05:00.290 --> 05:01.610 That's going to be a timer. 05:01.610 --> 05:06.650 And as I told you, everything we're going to do will use shared pointers. 05:06.650 --> 05:15.020 So we have another thing that is called shared as you can see shared Peter okay. 05:15.050 --> 05:16.610 That's kind of a helper. 05:16.640 --> 05:20.690 You see that's so here it's written a shared pointer. 05:20.690 --> 05:26.690 Basically it's going to create an STD shared pointer of this class here of this object okay. 05:26.690 --> 05:31.460 So that's a helper that you can use instead of writing STD shared pointer. 05:31.460 --> 05:37.490 So we create a timer here timer as a private attribute. 05:37.490 --> 05:42.500 And then okay before I create the timer I'm going to create the callback. 05:42.830 --> 05:50.180 So let's do void timer callback I just create a function here a method. 05:50.180 --> 05:59.380 And let's just do Lclc-rp info with this gets longer. 05:59.560 --> 06:02.470 You can see how Autocompletion is very useful. 06:02.500 --> 06:03.610 And then. 06:03.670 --> 06:04.450 Hello. 06:04.540 --> 06:06.580 Okay, so code is valid. 06:06.580 --> 06:08.500 And in the constructor. 06:08.500 --> 06:12.820 So after I create the log I'm also going to create a timer. 06:12.820 --> 06:18.640 So I'm going to use this timer and say that the timer is equal to. 06:18.670 --> 06:22.690 And we have a function inside node that is. 06:22.690 --> 06:24.100 So I'm going to use the this keyword. 06:24.100 --> 06:27.220 Once again you don't have to okay. 06:27.250 --> 06:32.140 It's just for me to make it super explicit that when I use this it's about the node class. 06:32.620 --> 06:36.670 Create wall timer okay. 06:36.700 --> 06:38.950 And you can see it is recognized. 06:39.190 --> 06:41.140 So you can use the Autocompletion. 06:41.140 --> 06:46.630 And so here we need you see we need to give a STD chrono duration. 06:46.630 --> 06:51.550 So for example I'm going to use STD and then Chrono. 06:52.180 --> 06:59.070 And then I can use seconds because I just want one second which is going to be an integer here. 06:59.100 --> 06:59.550 Okay. 06:59.580 --> 07:02.190 So first that's going to be the period. 07:02.190 --> 07:07.380 So every one second and then I need to give the callback. 07:07.680 --> 07:13.140 I'm going to go back to a new line here and align that here. 07:13.950 --> 07:14.580 Okay. 07:14.580 --> 07:17.640 And how to link the callback. 07:17.670 --> 07:21.870 Well we need to use the std bind function. 07:21.870 --> 07:24.390 What do we need to do inside the Stdbind function. 07:24.390 --> 07:29.310 We need to give the reference to the callback with this symbol. 07:29.490 --> 07:33.090 So the ampersand and then my node. 07:33.090 --> 07:39.270 That's the class name plus timer callback. 07:39.270 --> 07:43.050 That's the name of the function without the parentheses. 07:43.080 --> 07:47.490 Okay, we are not calling the function, we are just referencing it. 07:47.490 --> 07:48.990 So I need to do this. 07:48.990 --> 07:51.120 And then I need to bind with this. 07:51.120 --> 07:55.710 So this is this class this object that I'm binding to. 07:55.740 --> 07:56.340 Okay. 07:56.430 --> 07:58.820 And let's not forget the semicolon. 07:59.120 --> 08:03.980 So this stdbind, I know the first time that you use that, it's a bit confusing. 08:03.980 --> 08:08.510 Everything you need to write inside, but well, once again, as you get used to it, it's always the 08:08.510 --> 08:09.290 same thing. 08:09.290 --> 08:13.490 And to complete this example, right now I'm just going to create a counter here. 08:13.490 --> 08:17.030 So let's do encounter same thing. 08:17.030 --> 08:20.960 I use a trailing underscore when I create an attribute in a class. 08:21.110 --> 08:22.970 It's just a convention that I follow. 08:23.120 --> 08:24.650 So I create a counter. 08:24.650 --> 08:29.570 I initialize it here to zero. 08:30.410 --> 08:33.920 And then I can use it in this method. 08:33.920 --> 08:35.060 So hello. 08:35.060 --> 08:39.890 And then percentage D counter. 08:40.010 --> 08:45.500 So you see we just create a string like you would do with printf or something like that. 08:45.500 --> 08:54.320 So percentage d and then colon and you put the variable and let's not forget to do counter plus plus 08:54.320 --> 08:56.420 to add one to the counter every time. 08:56.440 --> 08:57.850 And that looks good. 08:57.850 --> 08:59.560 So let's do a quick recap. 08:59.560 --> 09:02.800 We have created our class here okay. 09:02.920 --> 09:06.370 So when we start our program what's going to happen. 09:06.370 --> 09:09.220 First we're going to initialize Ros2 communications. 09:09.250 --> 09:09.940 Great. 09:09.970 --> 09:14.260 Then we are going to create a shared pointer to my node. 09:14.260 --> 09:18.430 So we're going to create an object my node of the minute class. 09:18.430 --> 09:22.000 When we create the object the constructor is going to be called. 09:22.000 --> 09:23.740 So we call the parent constructor. 09:23.740 --> 09:25.570 We initialize the node with a name. 09:25.660 --> 09:27.670 And then we print hello world. 09:27.670 --> 09:32.590 And we register the timer callback here with a world timer. 09:32.590 --> 09:33.700 So we create a timer. 09:33.700 --> 09:38.260 And the timer says that we need to call this function every one second. 09:38.260 --> 09:41.020 So still nothing is happening with this timer. 09:41.050 --> 09:44.380 Then we exit from the constructor. 09:44.380 --> 09:47.050 We go to this line and we make the node spin. 09:47.050 --> 09:49.180 When the node spins it's going to be. 09:49.180 --> 09:50.680 So the execution is going to be stopped. 09:50.680 --> 09:53.050 Here the node will be kept alive. 09:53.050 --> 09:57.650 And all the callbacks that have been registered can now be called. 09:57.680 --> 09:59.540 And because we have created a timer. 09:59.570 --> 10:03.740 The timer says every one second we need to call the timer callback. 10:03.770 --> 10:09.830 So while the node is spinning, this timer callback will be called every one second. 10:09.860 --> 10:13.190 Then when we press Ctrl C that's going to stop the spinning. 10:13.190 --> 10:14.030 And then we shut down. 10:14.060 --> 10:16.040 We exit and that's it. 10:16.220 --> 10:18.470 So let's save this file. 10:18.500 --> 10:20.720 Make sure that you save this file. 10:20.720 --> 10:23.000 There is nothing else to do in the cmakelists.txt. 10:23.030 --> 10:23.210 Okay. 10:23.240 --> 10:25.520 It's already been done previously. 10:25.520 --> 10:30.350 And let's go back to the terminal and let's do again build. 10:32.870 --> 10:37.640 And then source and then run. 10:37.910 --> 10:45.920 And you see we have hello 01234 etc. and I press Ctrl C and that's it. 10:45.950 --> 10:46.430 Great. 10:46.430 --> 10:51.890 So you have successfully created a C plus plus node with object oriented programming. 10:51.890 --> 10:56.720 And you also have seen how to create your first timer with a callback.