1 00:00:00,240 --> 00:00:05,580 OK, everybody, so this is going to be an extra lecture here on smart pointers. 2 00:00:06,450 --> 00:00:11,550 In the last lecture, we went over a smart pointer called Unique Pointer, but there was some feedback 3 00:00:11,550 --> 00:00:15,400 on the course that people really want to know about the other smart pointers. 4 00:00:15,420 --> 00:00:20,010 I wasn't going to include them because I thought it was just something more specific to learning C++ 5 00:00:20,010 --> 00:00:20,460 itself. 6 00:00:21,800 --> 00:00:23,300 Less of a general programming thing. 7 00:00:23,930 --> 00:00:29,570 But I will go ahead and go over it because it seems like, you know, it might be useful and there's 8 00:00:29,570 --> 00:00:33,890 interest in it, so I'm going to go over to other pointers, one called shared pointer and one called 9 00:00:33,890 --> 00:00:34,460 weak pointers. 10 00:00:34,460 --> 00:00:36,950 So those are the two other pointers. 11 00:00:36,950 --> 00:00:40,790 There's three in total unique shared and weak smart pointers. 12 00:00:40,790 --> 00:00:42,920 So I've made a little program here. 13 00:00:43,040 --> 00:00:47,300 It's called Speed CBP and I've put some stuff in here. 14 00:00:47,300 --> 00:00:49,610 We have a class that's just called something. 15 00:00:49,610 --> 00:00:58,220 You notice that it has a public constructor and destructor, as well as a little method or member function 16 00:00:58,220 --> 00:01:02,420 here called Get Thing, which just prints out this one private data member, right? 17 00:01:02,960 --> 00:01:11,900 So what we've done so far is just make a unique pointer like this right and type something, and we 18 00:01:11,900 --> 00:01:15,860 can just call this, you know, like you P1 and we've done something like this. 19 00:01:18,320 --> 00:01:21,330 So this will just make a unique pointer, right? 20 00:01:21,380 --> 00:01:25,220 And if I go, what I can do 21 00:01:28,970 --> 00:01:32,480 is like, let's say I make two of these right like you P1 and you P2. 22 00:01:32,480 --> 00:01:37,730 And what we talked about was when this when these pointers go out of scope, which is here in the function, 23 00:01:37,730 --> 00:01:37,940 right? 24 00:01:37,940 --> 00:01:40,910 Once it gets past this bracket returns zero and goes past year. 25 00:01:41,180 --> 00:01:46,100 That's when these two go out of scope and they automatically will d allocate themselves. 26 00:01:46,430 --> 00:01:48,560 They will automatically call the destructor right. 27 00:01:49,010 --> 00:01:52,160 And here is the destructor, and it prints out the allocated something. 28 00:01:52,160 --> 00:01:54,170 So we should see this printout twice, right? 29 00:01:54,770 --> 00:02:02,060 So if I go back here, I compile this and it's just going to be out, I noticed this SD allocated something 30 00:02:02,060 --> 00:02:03,020 twice, right? 31 00:02:04,490 --> 00:02:07,250 So that's what we've been doing so far. 32 00:02:07,730 --> 00:02:16,110 So another thing that I'd like to point out is that there is another way to make these pointers first. 33 00:02:16,130 --> 00:02:20,960 So what you can actually do is you don't have to use this syntax right here. 34 00:02:21,530 --> 00:02:27,920 What you can instead do is like you P2 equals and then this is a special kind of constructor constructor 35 00:02:27,920 --> 00:02:28,190 here. 36 00:02:28,730 --> 00:02:36,400 It's actually called make unique and you just say type something right here and you can put some little 37 00:02:36,410 --> 00:02:37,490 parentheses like that. 38 00:02:37,880 --> 00:02:40,280 This is kind of a preferred way to do it. 39 00:02:41,510 --> 00:02:42,680 These will both work. 40 00:02:42,800 --> 00:02:52,520 The only thing is that when you use this special kind of way of allocating the memory for a unique pointer, 41 00:02:52,520 --> 00:02:58,690 it actually uses something out of this code base here, and it can deal with exceptions. 42 00:02:58,700 --> 00:03:01,580 So we've in this course, we talk a little bit about exceptions. 43 00:03:02,330 --> 00:03:07,940 If you do it like this, you may run into some issues if you are dealing, with some exceptions to do 44 00:03:07,940 --> 00:03:08,480 with the pointer. 45 00:03:08,750 --> 00:03:15,410 So this is kind of known as a better syntax to use to make it, although this is totally acceptable 46 00:03:15,410 --> 00:03:17,060 most of the time too as well. 47 00:03:18,140 --> 00:03:22,430 So I just want to point that out, and we will be needing to use this style of syntax for the other 48 00:03:23,030 --> 00:03:23,660 smart pointer. 49 00:03:23,670 --> 00:03:27,250 So let's get into the next type of smart pointer. 50 00:03:27,260 --> 00:03:32,210 So the thing about the unique pointer that we mainly talked about is it just goes out of scope and it's 51 00:03:32,210 --> 00:03:33,260 basically done right. 52 00:03:33,260 --> 00:03:35,390 It makes a new piece of memory. 53 00:03:35,750 --> 00:03:38,840 And then once it goes out of scope, it's totally done. 54 00:03:38,850 --> 00:03:43,210 So a question that would lead us to talk about the next type of smart pointers. 55 00:03:43,220 --> 00:03:45,260 What if we wanted to do something like this? 56 00:03:45,980 --> 00:03:47,920 We just wanted to make another pointer, right? 57 00:03:48,260 --> 00:03:53,720 Well, like, hey, we have a smart pointer that's pointing to, you know, up one right? 58 00:03:53,720 --> 00:03:55,510 Or it's pointing to a new something. 59 00:03:55,670 --> 00:03:56,600 Let's call up one. 60 00:03:56,600 --> 00:03:58,670 And what if I just want to make another pointer, right? 61 00:03:59,540 --> 00:04:04,940 Well, this is pointing to the same piece of memory once this goes out of scope, basically, you know, 62 00:04:04,940 --> 00:04:07,370 this one is automatically deleted. 63 00:04:07,940 --> 00:04:10,430 So and you don't actually, this is going to be a problem. 64 00:04:10,430 --> 00:04:14,900 You won't be able to actually do this even right here because it's not really meant for this type of 65 00:04:14,900 --> 00:04:15,200 thing. 66 00:04:15,200 --> 00:04:20,210 It's only meant to be like a unique standalone point of view, hence why it's called unique pointer. 67 00:04:20,220 --> 00:04:22,130 So what if I try and compile this right here? 68 00:04:24,110 --> 00:04:29,420 So it actually says no, it has an error and it says like use of deleted function. 69 00:04:29,630 --> 00:04:34,730 And that's because if you look at the code base of unique pointer where it's written and implemented, 70 00:04:34,730 --> 00:04:39,710 it actually does, you know, just delete it so you can't actually use this anymore. 71 00:04:39,740 --> 00:04:40,580 It's just done. 72 00:04:40,940 --> 00:04:45,170 So you cannot make a copy with the assignment operator right here. 73 00:04:46,630 --> 00:04:47,140 So. 74 00:04:48,400 --> 00:04:53,230 What do we do if we want to do something like this, we are not going to use a unique pointer, but 75 00:04:53,230 --> 00:04:57,730 what we are going to use is something called a shared a pointer because we're going to share the same 76 00:04:57,730 --> 00:04:59,140 region of memory, right? 77 00:04:59,950 --> 00:05:04,250 So we can make a shared pointer call up to equals update one. 78 00:05:04,270 --> 00:05:11,650 So what we really should do is instead, I make like a shared pointer right here. 79 00:05:11,650 --> 00:05:20,250 But what I'm going to do is I'm going to instead make make it using that different style, right? 80 00:05:20,650 --> 00:05:22,810 That different style of allocating. 81 00:05:23,050 --> 00:05:31,300 So I'm going to say, firstly, make shared instead of make unique and I'm going to say something just 82 00:05:31,300 --> 00:05:31,840 like that. 83 00:05:32,410 --> 00:05:37,330 And what I can do is I'll just say ESP two equals ESP one. 84 00:05:37,330 --> 00:05:42,640 So this is the type of thing I would want to do if I want to make like another pointer pointing to the 85 00:05:42,640 --> 00:05:44,020 same piece of memory. 86 00:05:45,030 --> 00:05:50,490 And this is how I would want to initialize it in the beginning, right, if I make the initial shared 87 00:05:50,730 --> 00:05:58,920 or one, I would want to use this special part of coming from the memory code base there and say, make 88 00:05:58,920 --> 00:05:59,370 shared. 89 00:06:00,030 --> 00:06:03,960 So what's cool about this, though? 90 00:06:03,960 --> 00:06:05,320 Like what's the why would we use this? 91 00:06:05,340 --> 00:06:11,940 Well, of course we talked about this, but another really cool thing is that once this shared pointer 92 00:06:12,120 --> 00:06:14,550 SP1 one goes out of scope. 93 00:06:15,500 --> 00:06:19,310 It doesn't necessarily allocate the object. 94 00:06:20,680 --> 00:06:20,990 Right. 95 00:06:21,020 --> 00:06:25,420 So let me just let me show you kind of like what's going on here. 96 00:06:25,420 --> 00:06:31,740 So this only makes one piece of memory, right? 97 00:06:31,750 --> 00:06:34,510 So if I go ahead and run this right now? 98 00:06:36,240 --> 00:06:37,590 Compile it and run it. 99 00:06:38,580 --> 00:06:40,710 It only says the allocated something once. 100 00:06:41,220 --> 00:06:44,800 And that's because this is the only real allocated memory. 101 00:06:44,820 --> 00:06:48,180 This is just another pointer pointing to the same memory. 102 00:06:48,600 --> 00:06:56,580 The really cool thing, though, is that once SP1 goes out of scope, it doesn't delete it right then. 103 00:06:58,410 --> 00:06:58,740 Right. 104 00:06:59,190 --> 00:07:04,080 So if I weren't right here, I'm just going to put some sort of like, you know, scope block. 105 00:07:04,800 --> 00:07:16,890 So if I put something in here, let's just say I make another thing here, so we'll have a shared pointer 106 00:07:17,040 --> 00:07:18,320 SP1 here. 107 00:07:18,330 --> 00:07:21,690 Actually, I'm going to put this in here. 108 00:07:23,190 --> 00:07:25,500 I'm going to have another thing up here. 109 00:07:25,800 --> 00:07:32,340 So if I say shared pointer something and I'll just call this like s 110 00:07:36,090 --> 00:07:43,680 and what I will do is, I will say s equals one. 111 00:07:47,500 --> 00:07:51,940 Right here, so I'm declaring one up here, right, and then I make one here and I'm pointing this, 112 00:07:52,420 --> 00:07:56,080 I'm basically copying like, I'm making another pointer. 113 00:07:56,080 --> 00:08:00,070 This and this is right here is pointing to the same region of memory as this right here. 114 00:08:00,070 --> 00:08:01,330 This spun right. 115 00:08:01,690 --> 00:08:03,280 So shared another shared pointer. 116 00:08:05,010 --> 00:08:12,330 This shared pointer, they all share this one like control block is what it is like a one piece of memory, 117 00:08:12,340 --> 00:08:12,600 right? 118 00:08:12,600 --> 00:08:17,280 And it keeps track of how many pointers you have pointing to that memory. 119 00:08:17,550 --> 00:08:21,030 It's like special in that sense that it keeps track of all the references. 120 00:08:21,030 --> 00:08:22,110 It has a reference count. 121 00:08:22,110 --> 00:08:25,710 How many pointers are referring to this one control block of memory? 122 00:08:26,820 --> 00:08:29,130 In this case, there's two, right. 123 00:08:29,130 --> 00:08:34,020 We have one right here pointing to it, and then we have this one pointing to the same block of memory, 124 00:08:34,020 --> 00:08:34,290 right? 125 00:08:35,250 --> 00:08:40,410 This is the really cool thing is that this was created in this scope of this. 126 00:08:40,410 --> 00:08:46,320 If, right, once this goes out of scope, you would think if it was like unique pointer, it would 127 00:08:46,320 --> 00:08:50,070 delete it and we would no longer have access to that region of memory. 128 00:08:50,070 --> 00:08:57,090 So we wouldn't be able to do something, for example, like s get thing right. 129 00:08:58,590 --> 00:09:01,530 So what if I wanted to, you know, that's going to print out the thing. 130 00:09:01,530 --> 00:09:02,070 So. 131 00:09:04,140 --> 00:09:07,470 You would think that I wouldn't be able to do this right because this memory would be gone. 132 00:09:08,700 --> 00:09:10,530 Well, it's actually totally fine. 133 00:09:11,190 --> 00:09:15,030 So I'll show you it'll go ahead and print it out. 134 00:09:15,600 --> 00:09:20,880 So if I compile this and I run it, you know, there was no compiler errors there and noticed that it 135 00:09:20,880 --> 00:09:23,260 printed it out and then it dislocated it, right? 136 00:09:23,280 --> 00:09:30,960 And so what it was really doing is it waited until this one went out of scope, right? 137 00:09:30,980 --> 00:09:34,190 This is the last reference pointing to that region of memory. 138 00:09:34,200 --> 00:09:37,230 So it waited for us to go out of scope here. 139 00:09:37,560 --> 00:09:42,510 That's why we saw this thing is zero originally right? 140 00:09:42,510 --> 00:09:43,710 And it printed out here. 141 00:09:43,710 --> 00:09:48,420 So we saw it print out here before the allocated it right was the allocated. 142 00:09:48,420 --> 00:09:49,890 Something happened after that. 143 00:09:51,270 --> 00:09:56,010 You know, if we go here, you notice that zero printed out and then reallocated something printed out. 144 00:09:57,120 --> 00:10:01,830 So that means that the SE did not get the allocated until down here. 145 00:10:02,010 --> 00:10:07,860 So what it does is that the shared pointer keeps track of all of the references and the reference count, 146 00:10:08,310 --> 00:10:13,080 and it's not going to delete the region of memory. 147 00:10:13,080 --> 00:10:19,350 It's not going to allocate it until all of the reference cat like the very last pointer pointing to 148 00:10:19,350 --> 00:10:20,580 it goes out of scope. 149 00:10:20,760 --> 00:10:22,470 That's when it's going to be allocated. 150 00:10:22,860 --> 00:10:24,300 So that's what's cool about the SharePoint. 151 00:10:24,420 --> 00:10:29,310 Like, we can make a lot of things pointing to the same region of memory, and we don't have to like, 152 00:10:29,310 --> 00:10:36,150 rely on being in the same scope and having that memory like it deleted, you know, like a unique pointer 153 00:10:36,150 --> 00:10:37,640 would have totally gone out of there. 154 00:10:37,650 --> 00:10:42,390 The problem is we can't we weren't even able to assign, you know, another thing to the unique pointer. 155 00:10:43,540 --> 00:10:47,980 So we couldn't even test that out if I wanted to do the same thing with unique pointer because I cannot 156 00:10:47,980 --> 00:10:53,200 like make something else pointing to the same region of memory since it's unique. 157 00:10:54,160 --> 00:11:00,640 So that is a really cool thing about the shared pointer, and I can make as many references as I want 158 00:11:00,640 --> 00:11:06,910 to to this one region of memory that was originally, you know, SP1 was pointing to it originally. 159 00:11:07,120 --> 00:11:10,900 I can make a bunch more shared pointers pointing to the same thing, and they could all be at their 160 00:11:10,900 --> 00:11:12,160 own levels of scope. 161 00:11:12,610 --> 00:11:21,610 And I wouldn't have to worry about the, you know, memory going being allocated before these other 162 00:11:21,610 --> 00:11:24,320 pointers that I made going or going out of scope. 163 00:11:24,350 --> 00:11:26,200 You know, if I want to still access them. 164 00:11:27,700 --> 00:11:35,290 So there is one more type of pointer and that is a weak pointer. 165 00:11:35,590 --> 00:11:44,020 So the weak pointer is similar to the shared pointer, except it doesn't add another reference count 166 00:11:44,110 --> 00:11:49,660 like noticed that this thing added another reference count to the shared pointer, right? 167 00:11:49,710 --> 00:11:52,870 It has this control block, and it's keeping track of all the references. 168 00:11:53,110 --> 00:11:54,490 How many references are there? 169 00:11:54,850 --> 00:11:59,650 A weak pointer would be something that I guess you would only want to use temporarily because it wouldn't 170 00:11:59,650 --> 00:12:04,240 be considered, as you know, an extra reference count. 171 00:12:04,240 --> 00:12:16,140 So if I made this like a weak pointer, so I make this weak point s, then it's not going to be considered 172 00:12:16,150 --> 00:12:16,870 reference count. 173 00:12:16,900 --> 00:12:20,380 So when this goes out of scope, it'll totally be out of scope.