WEBVTT 00:00.080 --> 00:03.680 Let's now see how to use parameters in your Cplusplus nodes. 00:03.680 --> 00:09.020 So I encourage you to first watch the previous lesson on Python where I detailed everything. 00:09.020 --> 00:09.290 Here. 00:09.290 --> 00:14.330 I'm going to focus more on the syntax because in the end the parameters will are going to work exactly 00:14.330 --> 00:17.090 the same between Python and Cplusplus. 00:17.090 --> 00:19.070 So I'm going to go back to the code. 00:19.070 --> 00:24.290 Well here we have the Python code and the cplusplus code. 00:24.290 --> 00:27.230 I'm going to add it into the number publishers cpp. 00:27.230 --> 00:33.140 So once again this is the code we have written for an activity with the topics section. 00:33.140 --> 00:34.490 And here what do we have. 00:34.490 --> 00:39.470 Well very simply we have a publisher a timer and we publish a number here. 00:39.470 --> 00:45.200 We publish the number two in this method that we call every one second with this timer. 00:45.200 --> 00:51.500 So now let's use parameters for those values so that we can provide a different value at runtime if 00:51.500 --> 00:51.980 we want. 00:52.160 --> 00:55.790 And there are two things you need to do for each parameter. 00:55.790 --> 01:02.840 You need to first declare it just to say that it exists within the node, and also set a default value. 01:02.840 --> 01:06.110 And then you need to get its value so that you can use it. 01:06.110 --> 01:07.520 And we're going to do that. 01:07.550 --> 01:10.580 What I'm going to do that directly inside the constructor. 01:10.610 --> 01:15.620 Usually I declare the parameters and I get them before I do everything else. 01:15.650 --> 01:17.270 How to declare a parameter. 01:17.300 --> 01:19.100 Well I'm going to use this. 01:19.100 --> 01:21.080 So this is not mandatory. 01:21.080 --> 01:24.650 But again it's to make it explicit that it's from the node class. 01:24.650 --> 01:29.810 And you have a declare parameter method. 01:29.810 --> 01:33.980 Here from the Clcp node class you need to give first a name. 01:33.980 --> 01:35.720 So that's going to be number. 01:35.720 --> 01:39.980 And then you can give a default value let's say two. 01:40.730 --> 01:41.480 All right. 01:41.480 --> 01:44.360 And you have declared one parameter in C plus plus. 01:44.360 --> 01:47.270 So after this line the number parameter will exist. 01:47.300 --> 01:48.800 The default value is two. 01:48.800 --> 01:55.130 And because the default value is two like this that's also going to set the data type for the parameter. 01:55.130 --> 01:57.620 And the parameter is going to be an integer. 01:57.680 --> 01:59.660 Let's declare a second one. 02:00.440 --> 02:02.090 Declare parameter. 02:02.120 --> 02:04.250 Let's call it timer period. 02:05.240 --> 02:08.900 And this one is going to be 1.0. 02:10.130 --> 02:10.460 All right. 02:10.490 --> 02:13.940 And after this those two parameters are declared. 02:13.940 --> 02:18.440 But if we just keep the code like this, well nothing is going to happen because the parameters will 02:18.440 --> 02:22.700 exist kind of within the node, but we don't use them within the code. 02:22.700 --> 02:28.190 So for example, instead of initializing the number here, I'm not going to do that. 02:28.190 --> 02:30.920 I'm going to say number. 02:31.610 --> 02:38.990 So that's the private attribute we have here that we're going to use to publish is equal to this get 02:39.020 --> 02:40.160 parameter. 02:40.490 --> 02:41.990 I need to provide the name. 02:41.990 --> 02:43.280 That's number. 02:43.400 --> 02:47.240 And this will give us a parameter object. 02:47.360 --> 02:49.610 You see an Clcp parameter. 02:49.610 --> 02:52.130 From this we can do dot. 02:52.130 --> 02:55.700 And then you can see in C plus plus it's a bit different than in Python. 02:55.700 --> 03:01.040 In C plus plus we have to do as and then the data type that we want. 03:01.040 --> 03:07.280 So this is an integer we do as int and that's a function. 03:07.280 --> 03:09.110 So we use the parentheses. 03:09.140 --> 03:09.710 All right. 03:09.710 --> 03:12.560 So that's going to get the parameter value as an integer. 03:12.560 --> 03:16.610 And then we set that inside the number which is an integer here. 03:16.610 --> 03:22.160 Then I'm going to do the same for the time period I could create a class attribute. 03:22.160 --> 03:30.590 But I'm just going to create a simple variable here double time period. 03:31.760 --> 03:36.350 And that's going to be this get parameter. 03:37.400 --> 03:39.140 We provide the name. 03:39.140 --> 03:44.150 So that's going to be the same as what we've declared here. 03:44.330 --> 03:49.550 And then we do as double because it's a double number. 03:49.580 --> 03:49.940 All right. 03:49.940 --> 03:52.700 So make sure that you match the type here. 03:52.700 --> 03:59.270 And then well once we have declared the parameters and once we have the values in the code we can use 03:59.270 --> 03:59.480 them. 03:59.480 --> 04:01.940 So number is already used here. 04:01.940 --> 04:03.620 And in the timer here. 04:03.620 --> 04:05.240 Instead of doing that. 04:05.240 --> 04:15.110 I'm gonna want a different ways to write that, but I'm going to do STD Chrono duration and use this 04:15.110 --> 04:18.530 syntax with double type. 04:18.860 --> 04:19.250 Okay. 04:19.280 --> 04:25.970 And I'm going to provide the timer period like that. 04:26.360 --> 04:26.600 Right. 04:26.600 --> 04:31.700 So I create a duration with the timer period that I got as a double from the parameters. 04:31.700 --> 04:32.810 And that's it for the code. 04:32.810 --> 04:37.730 So you see you're going to have a bunch of lines to declare and get the parameters at the beginning 04:37.760 --> 04:39.530 of your node constructor. 04:39.560 --> 04:44.390 Then you just use those values just like normal variables and attributes. 04:44.450 --> 04:46.070 Let's save. 04:46.070 --> 04:48.680 And we're going to go back to the terminal. 04:49.040 --> 04:53.930 Let's build in the raster workspace packages. 04:53.930 --> 04:59.720 Select my CP package. 05:02.420 --> 05:03.050 All right. 05:03.050 --> 05:17.060 And let's source here Source bash RC and let's do a Ros to run my Python package and number publisher. 05:17.570 --> 05:24.890 Actually, if I do the C plus plus code, better to launch the C plus plus code. 05:24.890 --> 05:30.800 So I have just run the number publisher from the C plus plus package, and we can see if I do Ros two 05:30.830 --> 05:34.880 topic equal with the number topic. 05:37.400 --> 05:44.510 We have two published every one second, simply because I haven't provided any value for the parameters 05:44.510 --> 05:47.450 so that the default value is going to be used. 05:47.480 --> 05:48.050 Okay. 05:48.080 --> 05:52.640 So once again when you declare a parameter the parameter just exists. 05:52.640 --> 05:59.210 So it means that when you do Ros two param list you will find the parameter here. 05:59.780 --> 06:01.460 Now you see we have more stuff here. 06:01.460 --> 06:04.280 But you can see we have the number and the timer period. 06:04.280 --> 06:07.670 So they exist and they have a default value. 06:07.790 --> 06:09.320 And then you can get them. 06:09.320 --> 06:13.820 And if you don't provide them at runtime the default value is going to be used. 06:13.850 --> 06:15.800 So now I can do that. 06:15.800 --> 06:16.880 And I can do. 06:16.910 --> 06:27.110 So actually let's clear and then Ross args dash p number let's say 20. 06:27.110 --> 06:37.160 And then another dash p time period which is going to be let's say 3.4 because that's the float number. 06:38.450 --> 06:44.120 And you can see for example here I have an error because I have forgotten a colon here. 06:44.330 --> 06:44.990 Okay. 06:46.070 --> 06:47.660 And now it's working. 06:47.660 --> 06:54.350 If I do Rostopic echo it's going to publish the number 20 every 3.4 seconds. 06:54.350 --> 06:56.960 And you can see we have the number here. 06:57.020 --> 06:58.160 So it's working. 06:58.160 --> 07:02.810 And one more thing we can test is what if you provide a parameter that doesn't exist. 07:02.840 --> 07:07.370 So let's say you have a typo or maybe you provide a parameter that. 07:07.370 --> 07:13.550 So this param doesn't exist with a value? 07:13.580 --> 07:14.030 I don't know. 07:14.060 --> 07:14.720 Three. 07:14.750 --> 07:16.580 Let's say you want to provide a string. 07:17.000 --> 07:19.430 So that's also not a type. 07:19.730 --> 07:21.020 What's going to happen. 07:21.260 --> 07:24.470 You see that it's still working. 07:24.500 --> 07:30.770 And if I do Rosetta param list, the parameter that we have provided here doesn't appear. 07:30.800 --> 07:31.340 Okay. 07:31.340 --> 07:37.940 So basically you can provide any parameter that you want even if it's not declared in this case it's 07:37.940 --> 07:39.320 just going to be ignored. 07:39.350 --> 07:39.890 Okay. 07:39.920 --> 07:45.590 If the parameter is not declared in the code and if you don't provide the exact same value, then you 07:45.590 --> 07:48.920 see it's not taken into account anyway. 07:48.920 --> 07:51.710 It doesn't appear in the parameter list. 07:51.740 --> 07:52.130 All right. 07:52.130 --> 07:59.870 So make sure also that when you provide the parameter name and value that this is exactly the same name 07:59.870 --> 08:03.590 that you have set here when you declare the parameter. 08:04.250 --> 08:04.640 All right. 08:04.640 --> 08:07.310 And that's it for parameters for C plus plus. 08:07.310 --> 08:09.710 So now you know how to use them in your nodes.