WEBVTT 00:01.340 --> 00:04.660 Memory and the C plus plus standard library here. 00:04.670 --> 00:11.960 This C plus plus standard library provides various classes to allow you manipulate collection of objects. 00:11.990 --> 00:18.680 These classes called the STL Standard Template Library. 00:18.680 --> 00:26.990 So this provides a standard way to insert items into collection objects and ways to access the items 00:26.990 --> 00:29.720 and iterate through the entire collections. 00:29.720 --> 00:31.460 This is called the Iterators. 00:31.460 --> 00:41.090 Here, the STL defines collections classes that are implemented as stacks or as a vectors with a random 00:41.090 --> 00:41.540 access. 00:41.540 --> 00:45.560 Here, these classes will be covered in depth in the next lecture. 00:45.560 --> 00:53.780 So in this section we will limit the discussion to just two classes that behave like C plus plus built 00:53.780 --> 00:54.740 in arrays. 00:54.770 --> 00:58.850 The first, let's begin with the standard library arrays here. 00:58.880 --> 01:09.620 The standard library arrays provides two containers that given random access via an indexer to the data. 01:09.620 --> 01:17.000 So these two containers also allows you to access the underlying memory, since they guarantee to store 01:17.000 --> 01:20.420 the items sequentially and contiguous in memory. 01:20.420 --> 01:24.800 And they can be used when you are required to provide a pointer to a buffer. 01:24.800 --> 01:32.330 So these two types are both templates, which means that you can use them to hold built in in the custom 01:32.330 --> 01:32.810 types. 01:32.810 --> 01:39.650 So these two collection classes are array and vector here. 01:41.950 --> 01:42.250 Yeah. 01:42.520 --> 01:43.960 So these are. 01:45.090 --> 01:48.360 These are the Wilton standard. 01:49.270 --> 01:50.290 Library. 01:51.230 --> 01:51.860 All right. 01:52.340 --> 01:57.020 So we can also use the stack based array class in C plus plus. 01:57.140 --> 02:05.360 Here the array class is defined in the array here, like that array header file here. 02:05.780 --> 02:12.680 So the class allows you to create fixed size arrays on the stack and with the built in arrays, they 02:12.680 --> 02:16.940 cannot shrink or expand at runtime. 02:16.940 --> 02:23.720 So since they are allocated on the stack, they do not require a call to a memory allocator at runtime. 02:23.720 --> 02:27.260 But clearly they should be smaller than the stack frame size. 02:27.260 --> 02:35.510 So this means that an array is a good choice for small array of items, so the size of an array must 02:35.510 --> 02:43.040 be known at compile time and it is passed as a template parameter like that. 02:43.040 --> 02:47.600 Here, for example, let's include a include array here. 02:50.010 --> 02:53.460 Ouray and Ouray. 02:54.530 --> 02:55.210 Here. 02:55.220 --> 02:57.920 Integer four and here. 02:57.920 --> 02:59.780 One, two, three, four. 03:00.790 --> 03:08.530 So in this code, the first template parameter in the angled braces is a type of each item in the array. 03:08.530 --> 03:12.520 And the second parameter is the number of items. 03:12.520 --> 03:21.670 So here number of items and the type of the each item in the array here. 03:21.670 --> 03:28.990 So this code initializes the array with an initialized list, but note that you still have to provide 03:28.990 --> 03:36.280 the size of an array in the template here and this object will work like a built in array or indeed 03:36.280 --> 03:40.450 any of the standard library containers with the ranged loop here. 03:40.450 --> 03:42.490 So let's create a range loop here. 03:42.790 --> 03:47.470 Integer E and here we created the array here. 03:47.470 --> 03:49.150 Make it here. 03:52.640 --> 03:57.870 Right here and we're going to create an array integer. 04:08.210 --> 04:08.510 Here. 04:10.360 --> 04:13.430 Firstly, we're going to create the array like that. 04:19.000 --> 04:22.750 Here and we're going to pass iterate through this array here. 04:26.310 --> 04:31.410 And each time we're going to print this on the screen. 04:34.300 --> 04:38.410 We have to import and use the namespace here. 04:40.460 --> 04:42.830 And print it out. 04:43.810 --> 04:47.080 As you can see, we printed our variables here. 04:47.110 --> 04:53.800 The reason is that our array implements the begin and end function that are required for this syntax. 04:53.800 --> 04:58.840 So you can also use this like that here, for example. 04:58.840 --> 05:16.450 INT for integer E zero oops, integer e equals zero, while e is less than r dot size here and plus 05:16.450 --> 05:20.900 plus E here and C out here. 05:21.220 --> 05:29.410 Our array here, our error E and n line here. 05:29.410 --> 05:32.230 We can write it also like that. 05:32.230 --> 05:33.940 It's the same output here. 05:33.970 --> 05:35.440 The size function here. 05:35.440 --> 05:41.740 As you can see here, we return the size of the array and the square braces. 05:41.740 --> 05:49.550 Indexer gives the random access to the members of the array so you can access the memory outside of 05:49.550 --> 05:51.220 the bounds of the array. 05:51.230 --> 06:00.170 So for the previously defined array that has four members you can access like this array r ten. 06:00.170 --> 06:05.360 So this may cause the unexpected behavior at runtime. 06:05.360 --> 06:06.410 Let's try it out. 06:07.300 --> 06:09.780 As you can see here, there's just a reprinted. 06:09.790 --> 06:11.260 There's a bunch of zeros. 06:12.060 --> 06:12.780 Here. 06:12.780 --> 06:19.720 So or this may cause unexpected behavior or even some kind of memory fault. 06:19.740 --> 06:27.960 So to guard against this, the class provides a function F which will perform, uh, perform a range 06:27.960 --> 06:28.340 check. 06:28.350 --> 06:37.830 And if the index is out of range, the class will throw the cplusplus exception, which, uh, here. 06:39.250 --> 06:39.580 Here. 06:40.920 --> 06:43.020 C plus plus exception named. 06:43.050 --> 06:45.390 Out of range here. 06:45.810 --> 06:49.020 So the main advantage of using an array. 06:49.410 --> 06:56.610 Array object is that you get compile time checks to see if you are inadvertently passing the object 06:56.610 --> 06:59.520 to a function as a dump pointer here. 06:59.910 --> 07:02.140 Let's make another example here. 07:02.160 --> 07:03.030 Void. 07:04.110 --> 07:04.500 Here. 07:05.960 --> 07:09.410 Void use an init. 07:10.180 --> 07:12.100 An integer pointer here. 07:12.400 --> 07:17.620 So at runtime the function does not know the size of the buffer passed to it. 07:17.620 --> 07:26.080 And in this case, the documentation says that you must pass a buffer with ten integer types variables. 07:26.080 --> 07:34.300 But as we see in C plus plus allows you allows a built in array to be used as a pointer. 07:34.300 --> 07:36.850 So we can do it like that. 07:37.210 --> 07:39.340 In practice use. 07:41.010 --> 07:41.730 Ten. 07:42.960 --> 07:43.830 Ah one. 07:43.830 --> 07:44.610 So. 07:45.510 --> 07:45.810 Oops. 07:49.500 --> 07:49.800 Here. 07:49.980 --> 07:55.410 Actually, let's create another array for this example and make comment out. 07:56.650 --> 07:58.540 Comment it in here. 07:59.440 --> 07:59.940 Okay. 07:59.950 --> 08:01.090 Integer array. 08:02.490 --> 08:02.880 Here. 08:02.880 --> 08:04.710 And one, two, three, four. 08:04.980 --> 08:07.650 This contains same variables as previous arrays. 08:08.040 --> 08:08.970 Here. 08:10.100 --> 08:17.050 And then this will read the past, the end of the buffer here. 08:17.060 --> 08:20.570 As you can see here, we got an exception. 08:20.570 --> 08:28.550 So this is no compiler checker nor any runtime check to um, catch this error. 08:28.760 --> 08:36.680 But there is the array class will not allow such an error to happen because there is no automatic conversion 08:36.680 --> 08:39.530 into a dump pointer here. 08:39.530 --> 08:48.320 So if you insist in obtaining a dump pointer, you can do this and be guaranteed to have access to data 08:48.860 --> 08:53.360 as a contiguous block of memory where the items stored sequentially. 08:53.720 --> 08:55.850 So you can do it like that. 08:59.460 --> 08:59.760 Here. 09:00.860 --> 09:01.880 Let's compile it. 09:04.250 --> 09:06.710 And, uh, here. 09:10.310 --> 09:14.690 We got Elder turned one Subcommand filed. 09:15.380 --> 09:20.750 That's why you don't have to do this like that with the dump pointers here. 09:20.960 --> 09:23.720 And we can. 09:25.780 --> 09:27.620 To test it like that here. 09:28.820 --> 09:30.500 Books are one. 09:31.860 --> 09:33.960 And data here. 09:38.330 --> 09:43.280 And as you can see here, this won't compile either. 09:43.280 --> 09:48.860 So this is not the correct, correct coding style here. 09:48.860 --> 09:56.030 And you will learn more about and how to correct this syntax in next lecture.