WEBVTT 00:00.060 --> 00:05.610 Hello again! In this video, we are going to look at copying algorithms. A copying algorithm 00:05.610 --> 00:06.720 does what you might expect. 00:07.050 --> 00:10.320 It will copy elements from one iterator range into another one. 00:11.070 --> 00:14.550 The main use for this is for populating sequential containers. 00:15.000 --> 00:20.610 So we have one container with some data in it, and we can use that data to populate an empty container. 00:22.230 --> 00:24.420 The basic algorithm is called copy(). 00:24.900 --> 00:25.260 We give 00:25.260 --> 00:28.800 it the iterator range of the container that we are copying from. 00:29.250 --> 00:33.330 And then an iterator range in the container where we want to copy the data to. 00:34.140 --> 00:38.600 This assumes that the vector is the right size, or that you are using an insert 00:38.640 --> 00:39.240 iterator. 00:42.480 --> 00:44.640 So here is some code for printing that out. 00:46.080 --> 00:51.960 We have a vector that we are going to copy, and then we have our call to copy(). 00:52.710 --> 00:55.290 So the first version with a vector of the correct size. 00:56.070 --> 00:59.430 Then we have another attempt with a insert iterator. 01:00.120 --> 01:02.460 And then finally, we use a handwritten loop. 01:03.090 --> 01:04.740 So these should all give the same answers. 01:05.850 --> 01:06.300 Okay. 01:08.870 --> 01:14.630 There's also a copy_n() algorithm, which will copy the first "n" elements from the range. 01:15.290 --> 01:19.310 So we can have copy_n(), the start of the iterator range, 01:19.580 --> 01:21.980 and then the number of elements that we want to copy. 01:22.670 --> 01:26.900 So that is equivalent to just leaping over the first two elements of the vector. 01:29.530 --> 01:36.610 And then, using the same vector again, we call copy_n() to copy two elements, and 01:36.610 --> 01:38.380 we also have the handwritten equivalent. 01:40.540 --> 01:41.110 So there we are. 01:41.350 --> 01:48.080 We only get the first two elements of the vector copied. And the final algorithm is 01:48.140 --> 01:54.940 copy_if(). So, this is a version of copy(), which will only do the copy if a predicate returns true. 01:55.810 --> 01:58.900 So we call this with the same arguments and a callable object. 01:59.490 --> 02:04.720 We are going to use our favourite lambda expression, which returns true for odd numbers and false for 02:04.720 --> 02:05.470 even numbers. 02:06.100 --> 02:11.830 And this will only copy the odd numbers from "vec" into "vec2". The even numbers will be ignored. 02:15.030 --> 02:22.650 And there is our call to copy_if(). And if we were doing this by hand, then we would have an if statement 02:22.920 --> 02:23.880 which does the same thing. 02:26.160 --> 02:30.480 So we get the odd numbers copied, but the even number is ignored. 02:32.430 --> 02:36.480 So you can think of copy_if() as acting as a kind of filter between the two vectors. 02:37.350 --> 02:45.180 So we have the data in "vec" and it gets passed into "vec2", but only if it meets this criterion. 02:45.780 --> 02:48.000 If it does not meet the criterion, it gets filtered out. 02:48.690 --> 02:53.570 So here, we are filtering out the even numbers, but you could do anything you want to really. So 02:53.570 --> 02:57.000 you can apply whatever filter is needed for your problem. 02:58.200 --> 02:59.760 Okay, so that is it for this video. 03:00.180 --> 03:03.060 I'll see you next time, but until then, keep coding!