WEBVTT 00:01.500 --> 00:06.000 Hello again! In this video, we are going to look at stream manipulators and formatting. 00:08.500 --> 00:13.420 A manipulator is something that gets pushed onto a stream to affect the stream's behaviour. 00:14.050 --> 00:17.760 We have already met the flush and endl manipulators. 00:18.790 --> 00:23.740 These affect these stream's behaviour, by causing it to flush the buffer immediately, instead of waiting 00:23.740 --> 00:25.030 until the buffer is full. 00:26.620 --> 00:33.280 The C++ library defines a number of manipulators for streams, and these alter the way that the stream 00:33.280 --> 00:34.420 formats the output. 00:35.140 --> 00:41.470 Most of these are in the iostream header, but there are some which are in iomanip, and that is for manipulators 00:41.470 --> 00:42.730 which take an argument. 00:47.030 --> 00:52.750 If you have tried to print out a Boolean, you will have noticed that it prints out the number 1 or 00:52.790 --> 00:55.160 0, and not the words "true" or "false". 00:56.360 --> 00:58.460 There is a boolalpha manipulator. 00:59.060 --> 01:02.060 And if we push that on the stream, then the stream will 01:02.060 --> 01:04.310 actually start printing out the words "true" or "false". 01:05.000 --> 01:06.920 And then that will change the state of the stream. 01:06.920 --> 01:11.480 So any Boolean expression you give to it will be printed out as true or false. 01:15.700 --> 01:17.030 So let's try this out. 01:17.050 --> 01:21.790 So first of all, we are doing it the traditional way, without doing anything special. 01:22.330 --> 01:24.250 We have a Boolean expression. 01:24.940 --> 01:31.390 And then we print it out again, using boolalpha. And then we try printing out something, else just to 01:31.390 --> 01:33.190 show whether the stream still does it. 01:35.610 --> 01:38.580 And the answer is that it does. This will affect the behaviour of the stream. 01:38.850 --> 01:43.230 And if you want to turn it back to the default, then you have to push "noboolalpha". 01:44.010 --> 01:47.640 So that will go back to the default behaviour of printing 1's or 0's. 01:52.010 --> 01:54.920 So if we do nothing, we get the number zero, for false. 01:55.670 --> 01:58.100 And then with boolalpha, it will print false. 01:59.570 --> 02:03.470 And if we try it again, without putting boolalpha this time, it still does. 02:04.010 --> 02:04.360 True. 02:05.300 --> 02:08.570 And then with noboolalpha, it goes back to printing numbers. 02:11.820 --> 02:17.490 So, boolalpha will change the state of the stream and noboolalpha will change it back to the default. 02:18.360 --> 02:22.080 By default, output streams do not perform any formatting on the data. 02:22.560 --> 02:28.920 If you print, for example, two variables, then it will use just enough room for the data in the first 02:29.310 --> 02:32.010 argument and then just enough room for the second. 02:32.640 --> 02:37.260 So they're going to be displayed like this. And quite often that is good enough. 02:37.260 --> 02:39.660 But maybe we want to have these lined up. 02:39.660 --> 02:41.400 So the five is right above the two. 02:45.560 --> 02:51.050 For example, if we have some results and we want to present them in a table. So we need to make 02:51.050 --> 02:56.720 all the outputs line up, and that means we need to make each output field the same width as the 02:56.720 --> 02:58.010 one below it or above it. 03:01.390 --> 03:08.680 There is a setw manipulator. So we can tell the stream how wide we want a field to be. The argument 03:08.680 --> 03:16.010 to setw is the width of the field. And this will only affect the next data item on the stream. 03:16.070 --> 03:19.090 setw takes an argument, so it is defined in iomanip. 03:22.030 --> 03:23.260 So let's have a look at this. 03:23.720 --> 03:26.620 We are going to display our "Penguins" and "Polar Bears". 03:26.800 --> 03:32.320 (Perhaps it is the football results, I do not know!) And we are going to set the width of the field to 15. 03:32.830 --> 03:34.870 So this means that it is going to use 15 03:36.340 --> 03:40.180 characters to present the data in "Penguins" and 15 for "Polar Bears". 03:40.300 --> 03:45.190 What it will actually do is to add some space characters to make the field the required width. 03:45.880 --> 03:46.900 So let's try that out. 03:49.980 --> 03:56.010 Well, we have got the "5" and the "2" matching up, but it is not quite what we wanted. The "Penguins" 03:56.010 --> 03:57.820 and the "Polar bears" are over here. 03:58.200 --> 03:59.670 We expected they would be over there. 04:00.330 --> 04:04.980 The reason for this is that by default, the space characters are added at the left. 04:05.490 --> 04:07.350 So the output lines up on the right. 04:07.770 --> 04:10.500 So this is what is known as "right-justified" output. 04:14.910 --> 04:19.050 There is another manipulator we can use to make the output "left-justified". 04:19.110 --> 04:25.710 So the "Penguins" and "Polar Bears" are going to be at the left of the field and this manipulation is called 04:25.710 --> 04:26.130 "left". 04:28.980 --> 04:35.790 So setw() will only affect the next output field, so "5" would have the normal width, but the "left" 04:35.790 --> 04:37.860 manipulator permanently changes the stream. 04:38.340 --> 04:40.650 That is what is known as a "sticky" manipulator. 04:41.160 --> 04:45.420 So when you make a change, it "sticks". Until you change it back. 04:46.380 --> 04:51.840 And if we want to go back to using the default, right-justified, then there is a "right" manipulator, 04:51.840 --> 04:52.620 which will do that. 04:55.160 --> 04:56.720 So let's try adding that... 05:00.220 --> 05:00.880 To our code... 05:03.520 --> 05:07.600 And then there we are, we get the "Penguins" and "Polar Bears" lined up at the left of the field. 05:15.370 --> 05:20.500 So a manipulator is said to be "sticky" if it permanently changes the state of the stream. 05:21.010 --> 05:23.710 And in fact, that applies to most of the manipulators. 05:24.250 --> 05:29.710 So the stream will remain in the same state, until we push another manipulator, which has the opposite 05:29.710 --> 05:30.130 effect. 05:30.520 --> 05:37.210 So if we push "left" to make the output left-justified, its will remain left-justified until we push "right" 05:37.630 --> 05:39.400 to change it back to the default. 05:41.840 --> 05:46.100 If a manipulation is not sticky, it will only affect the next output operation. 05:46.820 --> 05:51.200 So this applies to setw(). And, in fact, setw() is the only one which is not "sticky". 05:51.770 --> 05:53.450 So this is typical C++! 05:53.450 --> 05:56.810 There's always one exceptional case, one which does not follow the rules. 06:01.250 --> 06:05.930 And then finally, if you do not want to have spaces as the padding character, you can change it to something 06:05.930 --> 06:06.230 else. 06:06.710 --> 06:11.270 So setfill(), and then that will make the argument the padding character. 06:14.680 --> 06:19.570 Again, this is a sticky manipulator, and you need to set it back to the default after you have used 06:19.570 --> 06:19.810 it. 06:21.430 --> 06:26.380 So there we are. The same code that we had before, but actually without the "left". So let's put that back 06:26.380 --> 06:26.650 in. 06:32.980 --> 06:40.420 And then we set the defaults back to right-justified as well. It is always a good idea to set the defaults 06:40.420 --> 06:40.930 back again. 06:41.470 --> 06:46.000 If you are working with other people and you change the defaults to something they are not expecting, 06:46.360 --> 06:47.850 then you are probably going to annoy them. 06:47.890 --> 06:50.860 So we want to avoid annoying other people. 06:51.700 --> 06:56.330 If you're working in industry, then programming is all about teamwork. And part of teamwork is not 06:56.330 --> 06:56.920 annoying people! 07:00.110 --> 07:04.760 So there we are, instead of the space padding we have the has padding. And actually we still have one 07:04.940 --> 07:10.280 space character, because that was in the original expression. So perhaps we should remove that... 07:13.110 --> 07:14.670 To make things less confusing. 07:16.870 --> 07:21.190 So there we are, the padding character is now the hash symbol... 07:32.530 --> 07:35.830 And just to prove that things are back to normal - I do not know. 07:44.300 --> 07:45.770 Let's have 11 hippopotamuses. 07:49.230 --> 07:51.360 So you see, we've gone back to right justification. 07:51.810 --> 07:56.760 And incidentally, I think there is more than 15 characters in "hippopotamuses", so it has just spilt over. 07:59.230 --> 08:00.850 OK, so that is it for this video. 08:01.300 --> 08:04.090 I will see you next time, but meanwhile, keep coding!