WEBVTT 00:00.150 --> 00:07.470 Hello again! In this video, we are going to look at list operations. With C++ lists, we can do most of 00:07.470 --> 00:09.990 the operations that we can do on sequential containers. 00:10.530 --> 00:14.220 We can use push_back() and push_front() for adding elements to the container. 00:15.030 --> 00:19.350 We can use iterators to loop over some of the elements, or all the elements, in a list. 00:20.370 --> 00:24.540 One important difference is that lists do not support random access. 00:25.320 --> 00:26.460 With a vector or string, 00:26.460 --> 00:31.560 we can jump straight to the sixth element, for example. With a list we have to start at the beginning 00:31.860 --> 00:33.330 and iterate until we get there. 00:34.380 --> 00:40.020 So this means that the functions in the header, which require random access, are not supported. 00:40.560 --> 00:46.080 For example, if we try to call sort() with a list or a forward_list as argument, then that will not 00:46.080 --> 00:46.560 compile. 00:47.340 --> 00:54.300 Instead, this each member function we have to use, but that will work fine. And it is specialized to 00:54.300 --> 00:55.890 be efficient when sorting lists. 00:58.290 --> 01:02.790 Quite often, containers have member functions which have the same functionality as algorithms. 01:03.510 --> 01:09.390 In the case of list, these can sometimes be much more efficient than using the generic versions. For 01:09.390 --> 01:12.900 example, with remove(). We saw with the generic version with vector. 01:13.350 --> 01:17.610 It does not actually delete the elements from the container, it just moves them to the back 01:17.610 --> 01:25.020 of the container, and then you have to call erase(). The member function for list will actually delete the elements 01:25.020 --> 01:25.640 straightaway. 01:25.650 --> 01:30.970 So no messing around, and no call to erase(). And that just involves assigning a couple of pointers. 01:31.620 --> 01:36.210 So obviously, that is going to be much faster than calling the generic version and moving list 01:36.210 --> 01:36.690 elements arounf. 01:39.510 --> 01:44.040 So let's have a look at this remove() member function. In fact, first of all, let's check whether we 01:44.040 --> 01:45.630 can use the generic sort. 01:48.340 --> 01:51.550 And no, we get one of those horrible template errors. 01:54.220 --> 01:56.710 So let's go back to using the member function version. 01:57.430 --> 02:04.390 So here is our list. And then we are going to call remove(), using the member function. 02:04.840 --> 02:07.150 So this will remove the elements with value 3. 02:07.690 --> 02:09.010 It will delete it straightaway. 02:09.010 --> 02:10.750 So we do not need to call erase. 02:13.260 --> 02:19.350 So there is our list. There is the sorted version of the list, and there is the list after removing the 02:19.350 --> 02:20.610 element with value 3. 02:23.300 --> 02:28.910 So in general, if you're going to be moving elements around, it's much better to use the list member function 02:28.910 --> 02:30.260 than the generic algorithm. 02:30.740 --> 02:36.260 So that applies to things like reverse(), remove(), which we just saw, remove_if() and unique(). 02:39.440 --> 02:43.100 There are also some functions which are specific to lists. 02:44.360 --> 02:46.340 One of these is the merge() member function. 02:46.580 --> 02:52.100 So this takes another list as argument, and it will move all the elements from that argument list into 02:52.100 --> 02:53.870 the list that it was called on. 02:55.160 --> 02:59.930 So the result is going to be the combination of all the elements in the two lists, and the second 02:59.930 --> 03:01.070 list is going to be empty. 03:01.850 --> 03:06.530 If we sort both the lists before calling this, then the result will be sorted as well. 03:09.210 --> 03:11.310 So here we have two lists. 03:13.910 --> 03:19.400 We are going to sort them, using the member function, of course, and then we call merge() on "list1". 03:19.820 --> 03:23.720 So the elements from "list2" are going to be merged into "list1". 03:24.890 --> 03:28.500 So list1 is going to contain all the elements from both the lists, and list2 03:28.500 --> 03:29.660 is going to be empty. 03:33.750 --> 03:35.430 And that is what we get. 03:36.060 --> 03:39.960 So list1 has all the elements, and list2 is empty. 03:41.880 --> 03:44.610 Another member function is splice(). This time, 03:44.670 --> 03:49.260 we give it an iterator as the first arguments, so that is an iterator into the first list. 03:50.040 --> 03:54.510 And this will insert all the elements from the second list just before that iteration. 03:54.810 --> 03:56.610 So this is for the double linked list. 03:58.650 --> 04:01.530 We will see in a minute that the forward_list works slightly differently. 04:02.490 --> 04:07.940 And you can also provide a single iterator from the second list, which will just move one element. Or 04:07.950 --> 04:12.060 you can provide an iterator range, which will move some of the elements from the second list. 04:17.090 --> 04:19.360 So we have the same two lists again. 04:21.300 --> 04:24.980 We are going to an iterator to the second element of list1. 04:25.730 --> 04:31.080 Then we are going to pass that as the first argument to splice(), and then this will insert all the elements from 04:31.090 --> 04:34.670 list2 just before the second element of list1. 04:35.480 --> 04:39.500 So we expect to see 1, 9, 3, 14, 12 and so on. 04:43.070 --> 04:48.110 And there we are, the elements from list2 have been inserted just before the second element 04:48.110 --> 04:48.890 of list1. 04:52.290 --> 04:54.600 With forward_list, it works slightly differently. 04:54.630 --> 05:00.570 You will remember that, when we inserted into a forward_list, we had to use insert_after() instead of 05:00.570 --> 05:06.330 just insert(). And that would insert the new element after the operator, instead of before it, which 05:06.330 --> 05:07.380 all the other containers do. 05:07.920 --> 05:09.500 And the same thing works with splice(). 05:09.900 --> 05:13.890 splice() is really just inserting a whole list instead of a single element. 05:15.180 --> 05:22.260 So we have splice_after() instead of splice, and instead of inserting before an iterator, we insert after 05:22.260 --> 05:22.920 the iterator. 05:28.450 --> 05:31.870 So let's try this. So we have a forward_list with the same elements. 05:32.410 --> 05:36.460 And then we call splice_after(), with the an iterator to the first element of list1. 05:38.380 --> 05:40.030 And then we get the same results again. 05:40.420 --> 05:42.970 The elements are inserted after the first element. 05:43.900 --> 05:45.340 Okay, so that is it for this feature. 05:45.820 --> 05:46.630 I will see you next time. 05:46.630 --> 05:49.090 But until then, keep coding!