1 00:00:01,060 --> 00:00:04,930 OK, so welcome back to another lesson for object oriented programming. 2 00:00:06,040 --> 00:00:15,010 So in this lesson, we are going to talk about a few things you won't be as difficult as a lecture as 3 00:00:15,010 --> 00:00:15,690 previous ones. 4 00:00:15,700 --> 00:00:19,750 I'm not going to stuff as much information into it as previous lectures. 5 00:00:20,890 --> 00:00:28,660 So what we are going to go over is how to set up a kind of that object oriented programming multiple 6 00:00:28,660 --> 00:00:33,450 file situation here in Sea Lion. 7 00:00:34,750 --> 00:00:36,490 And then I'm going to. 8 00:00:37,830 --> 00:00:42,990 Show you a new concept called a decent destructor. 9 00:00:43,020 --> 00:00:46,470 It is similar to a constructor, but kind of the opposite thing. 10 00:00:46,950 --> 00:00:53,430 So rather than constructing an object, it will destroy an object and then we will finish up by looking 11 00:00:53,430 --> 00:00:59,490 at some pointers to objects just like we had pointers districts and we'll do dynamically allocated objects. 12 00:01:00,900 --> 00:01:02,340 So let's go ahead and get started. 13 00:01:03,150 --> 00:01:05,880 So right here, I just have made I've made a new project in here. 14 00:01:05,880 --> 00:01:09,660 I called it object oriented programming pointers to a folder. 15 00:01:10,260 --> 00:01:15,420 So I'm going to right click this folder and I'm going to say new and you notice that all this stuff 16 00:01:15,930 --> 00:01:16,440 pops up. 17 00:01:17,610 --> 00:01:26,100 Well, I'm actually going to say is, I'm going to say a C slash C++ header file, and I'm actually 18 00:01:26,100 --> 00:01:31,200 just going to call this car because I'm going to use the same car class. 19 00:01:32,100 --> 00:01:34,190 So I'm going to say a car. 20 00:01:34,200 --> 00:01:37,040 You can just leave this checked ad to targets. 21 00:01:37,050 --> 00:01:40,920 It doesn't really matter the targets as far as the compilation process, and we don't really need to 22 00:01:40,920 --> 00:01:45,570 compile the headers, but I'm just going to let it be added to the targets because it won't cause any 23 00:01:45,570 --> 00:01:46,260 problems right now. 24 00:01:48,390 --> 00:01:54,000 So I go ahead and add this, do you notice it nicely puts these macro guards here for us? 25 00:01:56,020 --> 00:02:00,280 So we get the macro guides here, and that even puts a little common here on that. 26 00:02:00,280 --> 00:02:04,330 And if so, all I do is copy paste some code here. 27 00:02:05,080 --> 00:02:09,310 So let me just go ahead and grab some code. 28 00:02:09,340 --> 00:02:14,800 I'm getting it from the window and I'm going to pay you the car class. 29 00:02:14,800 --> 00:02:17,350 So this is the definition. 30 00:02:18,440 --> 00:02:24,140 And then I'm actually going to show you how you can make some. 31 00:02:26,750 --> 00:02:33,110 A cool air and sea lion to deal with the implementation, so I'm actually getting it right, click this 32 00:02:33,110 --> 00:02:38,780 and say new, and this time I'm going to say C++ source file. 33 00:02:40,230 --> 00:02:43,920 So I will say, see slash C++ source file. 34 00:02:44,400 --> 00:02:50,850 We also could have done both of these by doing the C++ class, but I just am doing them separate. 35 00:02:52,090 --> 00:02:57,520 So this is going to be the class would have handled both of these at the same time, but now I'm actually 36 00:02:57,520 --> 00:03:03,400 saying explicitly, I'm going to make another source file, which this deep file. 37 00:03:06,610 --> 00:03:10,150 And then so what I can do is go in here and if I. 38 00:03:11,230 --> 00:03:16,450 If I do this, it can say generate definition for constructor car. 39 00:03:17,020 --> 00:03:23,110 So you notice I click that and what it does is it automatically created the constructor inside of this 40 00:03:23,110 --> 00:03:24,670 car that CBP file. 41 00:03:25,030 --> 00:03:32,230 It also went ahead and included Carnot CP for us, which is pretty cool. 42 00:03:34,840 --> 00:03:40,390 So we can do that for actually all of these, so I can just hover over this, I can say generally definition 43 00:03:40,390 --> 00:03:41,020 for that. 44 00:03:41,740 --> 00:03:46,260 Go back here, I could say generate definition for this and you can just keep going and it does all 45 00:03:46,280 --> 00:03:46,930 this code for you. 46 00:03:46,930 --> 00:03:53,050 It sets up the member function implementations for you in this implementation file card. 47 00:03:54,580 --> 00:03:56,680 So pretty nice thing for sure. 48 00:04:04,480 --> 00:04:07,180 Yeah, but you replace this. 49 00:04:08,780 --> 00:04:14,860 But yeah, I can go ahead and I'm going to finish just copying the rest because I don't really want 50 00:04:14,860 --> 00:04:22,870 to have to deal deal with all that, so I'm going to go ahead and grab it from afar right now. 51 00:04:25,560 --> 00:04:31,710 This is just a little too rough for me to type right now, so that's why I'm going to just kind of replace 52 00:04:31,710 --> 00:04:33,540 all this stuff here. 53 00:04:33,630 --> 00:04:40,260 Copy and paste, OK, so copy paste in all the stuff that we had previously in the implementation file 54 00:04:40,260 --> 00:04:41,250 of our car class. 55 00:04:42,540 --> 00:04:51,360 And then so now what I want to do is talk about this first new topic, which is the destructor. 56 00:04:51,660 --> 00:04:59,010 So the destructor is something that's very similar to the constructor, but it kind of cleans up the 57 00:04:59,010 --> 00:05:01,020 object in memory. 58 00:05:01,030 --> 00:05:04,920 So here is where we initialize that object, right? 59 00:05:05,550 --> 00:05:10,680 So what we're going to do to make it destructor is have something that looks a lot like a constructor, 60 00:05:11,370 --> 00:05:17,280 but the only difference is that it's going to have a tilde in front of it. 61 00:05:17,280 --> 00:05:24,720 So I'm going to say, tell the car and this one, I don't need to put anything inside of. 62 00:05:25,720 --> 00:05:31,870 These parentheses here, because I'm not it's not like we're passing explicit things to it. 63 00:05:32,680 --> 00:05:36,850 You know, you can also have a default constructor here, too. 64 00:05:37,330 --> 00:05:41,560 You notice that this right here is like a parameter based constructor. 65 00:05:42,070 --> 00:05:48,010 So we have our constructor accepting a bunch of parameters that the user sets, but we do not have like 66 00:05:48,010 --> 00:05:51,630 a basic variable default constructor, so we could put that as well. 67 00:05:51,630 --> 00:05:52,870 And you notice that highlights. 68 00:05:55,500 --> 00:05:59,310 So, you know, you could generate a definition for this, but C++. 69 00:05:59,880 --> 00:06:06,180 Well, go ahead and just have a default constructor for you as well, kind of automatically so you don't 70 00:06:06,180 --> 00:06:10,860 have to do that, but we do want to generate destructor just to have it in there. 71 00:06:10,870 --> 00:06:12,480 So I'll go ahead and click that. 72 00:06:12,480 --> 00:06:14,970 And now it makes a nice destructor for us here. 73 00:06:16,130 --> 00:06:17,900 In our implementation file. 74 00:06:19,100 --> 00:06:27,440 And so the thing about the destructor is it's kind of just called automatically when objects go out 75 00:06:27,440 --> 00:06:34,520 of scope and when I say that, I mean, like stack allocated objects, not dynamically allocated objects. 76 00:06:34,530 --> 00:06:37,970 So let's go ahead and make an example here. 77 00:06:38,030 --> 00:06:39,860 So I'm just going to put some code in here. 78 00:06:39,870 --> 00:06:43,970 Actually, I think I'll need to include 79 00:06:46,730 --> 00:06:47,660 extreme. 80 00:06:49,890 --> 00:06:55,560 And then one of my do is down here, I'm just going to print out a little message here, so I'm just 81 00:06:55,560 --> 00:07:06,210 going to say see out and inside the structure, cleaning up object. 82 00:07:08,770 --> 00:07:09,250 Cool. 83 00:07:09,490 --> 00:07:17,380 So I'm going to have to do this, so I'm not using namespace nastily, so Anderson here, just so you 84 00:07:17,380 --> 00:07:19,810 can see when the destructor is getting cold. 85 00:07:19,810 --> 00:07:25,030 So let's head over to main and I'm actually just going to copy paste some code here in Maine as well 86 00:07:25,040 --> 00:07:25,930 that we have before. 87 00:07:27,100 --> 00:07:33,700 So this is just making our car and car two objects, all that good stuff. 88 00:07:34,450 --> 00:07:37,720 So go ahead and paste that code here. 89 00:07:38,080 --> 00:07:44,380 I'm actually going to need to include a card h. 90 00:07:46,200 --> 00:07:50,010 So let me go ahead and paste this in here. 91 00:07:51,810 --> 00:08:00,780 So now I make a couple cars and we print out all of the information and stuff that we were before. 92 00:08:01,440 --> 00:08:06,420 Let's go ahead and try and compile and run this to see what prints out, and then we can see where the 93 00:08:06,420 --> 00:08:08,970 destructor is actually being called. 94 00:08:09,150 --> 00:08:12,450 So, you know, here is our here's our destructor. 95 00:08:12,450 --> 00:08:15,350 So we will see whenever we see this message print out. 96 00:08:15,360 --> 00:08:22,410 We know that in comparison to win this other stuff prints out, we can tell that once the objects are 97 00:08:22,410 --> 00:08:29,490 kind of out of scope, which means they're out of Maine's stack frame, then the structure will be called 98 00:08:29,490 --> 00:08:30,330 to clean that up. 99 00:08:31,400 --> 00:08:36,740 And just in a moment, we will be looking at a dynamically allocated objects using pointers and stuff, 100 00:08:36,740 --> 00:08:43,430 and we'll notice that the destructor can actually help us clean that up to accept that we have to explicitly 101 00:08:43,430 --> 00:08:46,340 delete dynamically allocated memory, remember? 102 00:08:46,880 --> 00:08:51,740 So let's go ahead and run this and see what we get. 103 00:08:54,440 --> 00:08:58,610 Cool, so you notice here that it printed out twice at the end of everything. 104 00:08:59,330 --> 00:09:00,470 So I'm going to try. 105 00:09:00,530 --> 00:09:01,060 Oh, cool. 106 00:09:01,070 --> 00:09:04,670 I can zoom in on the output as well, so hopefully that's easier for you to see. 107 00:09:05,390 --> 00:09:09,050 So this is all the standard stuff that we've seen print out before, right? 108 00:09:09,230 --> 00:09:17,180 We got these car miles like the initialized miles here that were sent to that constructor to add parameters. 109 00:09:17,960 --> 00:09:20,360 And then we see 12 blue, three seven black. 110 00:09:20,360 --> 00:09:23,760 This is all just from this code right here that we've seen before. 111 00:09:23,760 --> 00:09:25,160 It makes sense that it's printed out. 112 00:09:26,280 --> 00:09:29,360 You know, this is the last card I get Andy Card. 113 00:09:29,360 --> 00:09:32,000 I get paint right here on these two lines. 114 00:09:32,390 --> 00:09:39,400 And then once we leave the scope here, we notice that the destructor is called not once, but twice. 115 00:09:39,410 --> 00:09:40,740 And why is it called twice? 116 00:09:40,760 --> 00:09:44,750 Well, it's called for each object, and we made two objects. 117 00:09:45,230 --> 00:09:48,680 You can think of this class. 118 00:09:49,050 --> 00:09:55,760 Each object is a instance of all of this, you know, all of this file and all of this file. 119 00:09:56,660 --> 00:10:03,040 If you can think of it as a copy of this, like we have, you know, car is a copy of all of this and 120 00:10:03,040 --> 00:10:07,870 all of this together, and then Car two is a copy of all of this file and all of this file together. 121 00:10:08,890 --> 00:10:14,290 And so that's why when we made those two objects in Maine, once we leave the scope of Maine, it's 122 00:10:14,290 --> 00:10:16,630 time to clean up the destructing. 123 00:10:16,630 --> 00:10:19,510 It's called not once, but twice because we have two objects. 124 00:10:21,910 --> 00:10:24,700 So that's kind of just what the destructor does. 125 00:10:24,850 --> 00:10:26,890 It's not, you know. 126 00:10:27,810 --> 00:10:34,020 Incredibly interesting right now, maybe, but it is very important because we don't want memory leaks, 127 00:10:34,020 --> 00:10:34,380 right? 128 00:10:34,770 --> 00:10:36,420 We talked about memory leaks. 129 00:10:38,510 --> 00:10:46,040 With not cleaning up dynamically allocated objects, and, you know, this is something that is important 130 00:10:46,040 --> 00:10:52,430 just to clean up the object and its most common use case is that it will be called to clean up objects. 131 00:10:53,360 --> 00:10:59,270 If that is the case, something that you'll see later on is that if we have a class, there might be 132 00:10:59,270 --> 00:11:03,470 more code in here if we have a class that, let's say, 133 00:11:06,200 --> 00:11:09,050 has dynamically allocated. 134 00:11:10,830 --> 00:11:17,280 Members or something like that, one need to clean those up, like if we have some sort of container 135 00:11:17,490 --> 00:11:25,350 or data structure, something like that that is dynamically allocated and that is one of the data members, 136 00:11:25,380 --> 00:11:30,120 the like, you know, private or public, but most likely private data members. 137 00:11:30,510 --> 00:11:35,610 We all have to handle deleting that in this destructor. 138 00:11:35,610 --> 00:11:41,880 So we might have to like, iterate over certain containers that contain dynamically allocated objects 139 00:11:41,880 --> 00:11:45,060 and, you know, get rid of all the stuff in there. 140 00:11:45,060 --> 00:11:48,150 So if we had some sort of let's say we have like a vector. 141 00:11:49,500 --> 00:11:54,770 Of this class that was like right here, we had some vector in it, held a bunch of dynamically allocated 142 00:11:55,100 --> 00:11:57,650 memory like pointers to dynamically allocated memory. 143 00:11:57,830 --> 00:12:02,870 You might want to handle cleaning that up in the destructor of the class. 144 00:12:03,800 --> 00:12:08,270 So just kind of, you know, a little foreshadow of some stuff we might need to do in the future of 145 00:12:08,270 --> 00:12:08,870 this course. 146 00:12:09,260 --> 00:12:13,790 Most likely more towards the data structures and algorithms portion. 147 00:12:13,790 --> 00:12:18,620 But you never know we might encounter it in this first half of the course as well. 148 00:12:20,080 --> 00:12:24,970 So that shows where the instructors call, let's look at making some dynamically allocated objects here, 149 00:12:24,970 --> 00:12:32,440 so I'm going back to Maine, so I can say, I'm just say car. 150 00:12:37,490 --> 00:12:46,490 Same car cleaner car equals new car. 151 00:12:47,890 --> 00:12:52,270 So what I'm doing right now is I'm using this constructor. 152 00:12:53,320 --> 00:12:56,650 That has the perimeter as a surprise constructor. 153 00:12:56,710 --> 00:13:00,640 It's the one that takes parameters, not the default constructor, but. 154 00:13:02,980 --> 00:13:07,120 What I'm doing here, let me explain this line, so this is the data type right here. 155 00:13:07,150 --> 00:13:10,630 This is saying that the type of this data is car. 156 00:13:11,470 --> 00:13:17,590 This right here is, of course, saying, OK, well, it's going to be a pointer. 157 00:13:17,740 --> 00:13:21,610 You know, this is really actually going to be a pointer to a card data type. 158 00:13:21,610 --> 00:13:25,540 And the variable of this point is going to be called car. 159 00:13:26,410 --> 00:13:31,330 And then right here on the other side of the equals where of course, using the new keyword to dynamically 160 00:13:31,330 --> 00:13:34,540 allocate memory and create a new car object. 161 00:13:35,050 --> 00:13:41,230 So kind of similar to how he did structs, but what we're doing right now is we're doing we're using 162 00:13:41,230 --> 00:13:46,300 the parameter rise constructor of car, which is, you know, in the header. 163 00:13:46,630 --> 00:13:47,350 It is this. 164 00:13:47,950 --> 00:13:51,130 And in the implementation, of course it is this at the top. 165 00:13:51,760 --> 00:13:56,380 This is what we're calling when we're making this dynamically allocated object and we're creating a 166 00:13:56,380 --> 00:13:57,130 pointer to it. 167 00:13:57,470 --> 00:14:02,260 Of course, you notice these all turn red right now, and that's because we need to use an arrow, an 168 00:14:02,260 --> 00:14:02,650 arrow. 169 00:14:02,660 --> 00:14:08,290 You can see that it suggests that we can use the arrow so we can go ahead and click that, and it will 170 00:14:08,290 --> 00:14:13,180 change it automatically for us here as well so I can go through, hover and click. 171 00:14:14,280 --> 00:14:18,330 We're over this and click and just do that and all of this, which is kind of nice, honestly, because 172 00:14:18,330 --> 00:14:22,170 my wrist is a little bit hurt, so. 173 00:14:24,330 --> 00:14:30,600 And then you noticed that these are all just for car, but of course, we have car too is not being 174 00:14:30,600 --> 00:14:36,270 asked to be changed because we have not changed that to a dynamically allocated object. 175 00:14:37,500 --> 00:14:45,700 So since we dynamically allocate this, we're going to need to handle its deletion. 176 00:14:45,720 --> 00:14:48,120 So right now, we would have a memory leak. 177 00:14:48,360 --> 00:14:49,920 Let's go ahead and run the program. 178 00:14:52,740 --> 00:14:59,580 You notice that it only calls the destructor once now, and that's because the destructor got automatically 179 00:14:59,580 --> 00:15:06,150 called when this was a stack allocated object, which is like car to car to is the one that is responsible 180 00:15:06,150 --> 00:15:09,030 for this printing out right here, the destructor clean of the object. 181 00:15:09,030 --> 00:15:16,350 But since we have not explicitly called the delete key word on this dynamically allocated object, it's 182 00:15:16,350 --> 00:15:19,140 not deleting it and therefore it becomes a memory leak. 183 00:15:19,770 --> 00:15:20,680 So that's not good. 184 00:15:20,700 --> 00:15:22,860 So let's go ahead and handle the deletion of this. 185 00:15:22,860 --> 00:15:31,920 So down here I will say if you delete car and let's see what happens when I do that. 186 00:15:35,690 --> 00:15:42,800 So now you notice that, in fact, cause the destructor twice because it knows we wanted to delete that 187 00:15:42,800 --> 00:15:49,760 car object, it deletes not only car two this time, but it also first deletes car the original car, 188 00:15:49,760 --> 00:15:53,510 not car one, but this right here, which we had a point or two. 189 00:15:55,190 --> 00:15:58,550 So I'm just kind of kind of leave it at that. 190 00:15:59,030 --> 00:16:04,280 I think in the next lecture, I'm going to go over kind of an interesting concept. 191 00:16:04,280 --> 00:16:10,610 I wasn't going to do this at this point in time, but I think that it might be good to go over. 192 00:16:12,900 --> 00:16:20,610 Type of pointer that cleans itself up where you don't have to use the delete key word, so I might be 193 00:16:20,610 --> 00:16:26,880 going over that because I think that could be kind of useful, although I might not always use it in 194 00:16:26,880 --> 00:16:28,830 the in the course. 195 00:16:29,040 --> 00:16:34,770 But it is a really good thing to know because in modern C++, a lot of people are trying to use these 196 00:16:34,770 --> 00:16:40,710 things called smart pointers, where it's a little bit safer and you don't have to delete that, it'll 197 00:16:40,710 --> 00:16:41,670 clean up itself. 198 00:16:42,510 --> 00:16:48,540 So with that, I am going to finish up this lecture and I will see you in the next lecture.