WEBVTT 00:01.050 --> 00:05.440 In this lecture I want to broadly go over how our programs get built. 00:05.450 --> 00:08.370 So are able to run. 00:08.410 --> 00:12.780 So there are three main steps that have to happen. 00:13.670 --> 00:17.060 The first step is the preprocessing step. 00:17.060 --> 00:27.240 The next is the compilation and the last step is the what's called blinking so the preprocessor effectively 00:27.510 --> 00:35.790 replaces all the preprocessor Duret preprocessor directives in the program and paste the relevant info 00:35.850 --> 00:37.590 into the files themselves. 00:37.590 --> 00:45.890 So for example we have the line that I didn't cover before which says include IO stream. 00:46.320 --> 00:56.790 So the hash include is actually a directive preprocessor directive that says make sure that IO stream 00:56.790 --> 01:06.070 which is a part of the standard library has all the input and output it'll paste the entirety of IO 01:06.070 --> 01:09.510 stream into our our program. 01:09.550 --> 01:17.650 So that's why we're able to use things like C in and C out and actually output things and get things 01:17.650 --> 01:21.050 from the console. 01:21.070 --> 01:30.090 So after this is done the output of the preprocessor will be C++ files with absolutely no directives 01:30.090 --> 01:34.520 so they'll be here C++ files. 01:34.690 --> 01:43.960 And that goes into the next stage which is the compilation stage and the compilation stage will take 01:44.140 --> 01:54.950 all of the C++ files as input and then turns them into assembly code and then machine code and place 01:54.950 --> 02:03.410 them into these stored object files and U-Mass Why does it need to do this well. 02:03.710 --> 02:12.410 The machine can't actually run C++ machine can only run machine code which is actually the native language 02:12.440 --> 02:14.470 of the machine. 02:14.930 --> 02:22.730 So that's why everything has to be compiled down even further from C++ into something that the machine 02:23.450 --> 02:24.440 can understand. 02:24.440 --> 02:31.130 Remember I said computers are kind of dumb so they don't really know many languages and only really 02:31.130 --> 02:32.510 understand one. 02:32.600 --> 02:43.620 And this is machine language and here's a picture of kind of how the compiler works it'll take all our 02:43.620 --> 02:45.060 C++ files. 02:45.060 --> 02:55.450 In this case not c files and all these other assembly files and put them into these object files these 02:55.830 --> 02:57.810 relocatable object files 03:01.060 --> 03:07.340 and those object files will be input into the linker. 03:07.360 --> 03:14.610 We're not going to go over too much of the linker in this course but the linker takes all the object 03:14.620 --> 03:19.230 files as input and really kind of bundles everything together. 03:20.120 --> 03:26.900 Into our executable program it will take more than just our object files that take other things that 03:27.620 --> 03:28.660 we're not going to go over. 03:28.680 --> 03:31.500 But the idea is it will it. 03:31.560 --> 03:37.740 It does the assembling and creates the real program. 03:37.780 --> 03:42.130 Here's another diagram that sort of shows how this works. 03:43.140 --> 03:50.550 So there's one other line in our program that we still don't understand which is the using namespace 03:50.620 --> 03:51.980 SDD. 03:52.290 --> 03:58.800 And this has kind of nothing to do with the compiler or linker but I thought I'd throw this in here 03:58.800 --> 04:03.510 just to just for the sake of completeness really. 04:03.540 --> 04:12.430 So this namespace SDD is a way of organizing code. 04:12.510 --> 04:19.470 In fact just the namespace part of it and we use it because all of the identifiers which have all the 04:19.470 --> 04:31.720 names of things in our IO stream library like scene and C out they all exist in the standard namespace 04:31.740 --> 04:34.710 which is the standard library names. 04:34.710 --> 04:43.380 So if we didn't write the using namespace SDD we'd actually have to write SDD colon colon C out in the 04:43.760 --> 04:56.380 open colon C in so that Koehne colon is really says hey this object C Ouch belongs to this standard 04:56.380 --> 05:04.080 namespace so hopefully that clears up a little bit of those two lines. 05:04.090 --> 05:11.490 I want to sort of demystify them a little bit so that we can continue on and start learning about constants 05:11.500 --> 05:12.250 next time.