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In the terminals, so or command prompt, so it works easier for everybody.

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It's more accessible.

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So right now, I am actually in a folder that just has a little test file for for this.

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So I am actually going to.

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Hey, you can check it out if you would like it just as test us copy.

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So I just have like this really basic programming here where I have like a string says Hello world,

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I print out some stuff.

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And what we're going to do is just kind of step through this really basic program, and I'm just going

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to show you a few things on basic commands and GDB so you can start debugging that as well.

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And I might go ahead and change something in here and try and see if I can show you like an error that

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you might encounter, just like previously.

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So we we're out of here.

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And so you notice this isn't compiled yet.

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We just have this test does copy here.

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We don't have an executable in here yet.

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So I'm going to go ahead and compile a way to compile it.

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Because if you want to debug, what can you debug?

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Are you going to have to change the command for G Plus plus?

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We're going to just need to add something.

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So we're going do G Plus Plus and rather than just saying test, copy and dash.

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So we're actually going to add another kind of similar flag like Dash.

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Oh, it's a flag, right?

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It's a a thing that says we want to specify an output file.

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We're not actually going to add a dash and G.

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And what this stands for is to include something called a debug symbols.

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And that just makes it so we can actually kind of look at stuff inside of our program when we are using

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the new debugger.

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So we're going to do G Plus plus just gasbag test CP Dash O Test stuff out here right now, right?

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So went ahead and compiled that now if we do it, their command, we can see that there is a test study

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here.

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So what do we do now?

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Well, to invoke GDB?

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What we're going to do is just tap GDP and then do the executable, so test not exceed.

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So this brings up the GDP debugger here, so says the new GDP.

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Here's the version number, you know, talks a little bit about the licensing and stuff like that.

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It says this GDB was configured as many GW 30 to 32 bit.

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And here it has the website.

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If you would like to go check it out and this is for reporting bugs, but you shouldn't be too concerned

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about that right now.

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So how do we start using this?

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Well, it's just like the other debugger and we go ahead and maximize this now and.

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I think that hopefully this will be big enough for you to.

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To see everything.

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Wondering if I need to increase the.

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The size, I think it will be OK.

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So let's go ahead and you know what, I.

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Let me see.

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Properties.

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I'm actually going to try and increase the status a little bit about that.

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I think that's a little bit better.

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So we need to set some break points, right?

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So think back to the debugger we just looked at.

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We were setting some break points in there by clicking around the side and making a little red dot.

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This is a terminal based debugger, so it's not going to have that nice graphical nature where we can

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click on little drop down arrows and examine things.

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It's all going to be based in the command line with little like text commands.

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So what we're going to do to set a break point is you can say you can type out break or you can just

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say be for a shortcut.

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And I'm going to say I can actually just provide a breakpoint at a function.

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So I know there's a main function, right?

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So I can actually just say break main and it will set a breakpoint at main.

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What it says right here, though, is just a hex address.

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You notice this is hexadecimal right.

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So what it's really doing is is just setting a breakpoint at a specific memory address, you know?

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So we talked a little bit about sections of memory, right?

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There's like the the text segment.

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We have our code in memory and also, you know, we have the stack and all of that stuff.

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So this is just to address a memory where it's setting this breakpoint and it's going to stop there

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that address.

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But it just so happens to be main because we said, break me.

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So what we can do now is just type R to run the program and it will stop at our breakpoint.

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So you notice that says Breakpoint, one main at Tostart CP Line six.

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So this call six means Line six and you notice it shows us the line number and then it also says it's

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string as equals.

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Hello, world.

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So that was really the first line in our program.

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So if we want to kind of see more information about where we are, what zone we are in, we can actually

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type list and press enter and that will show us a little bit more.

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So you see the line numbers here.

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So Line six is where we're at, right?

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That's where we start.

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And then it shows this kind of a little bit of what comes after that.

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Right here on line seven, eight, nine and 10.

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So to move through the program like a step over command, what we're actually going to do is say next,

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or you can just type in.

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Sellers can type in and that will go to the next line.

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You notice we went from line six to line seven.

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We're now so see out s if I go.

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So when I'm on this line that says See out, outguess.

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It hasn't yet executed this line.

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It has stopped right before executing it.

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So another interesting thing that I can do is if I press enter, it will run the last command and I

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ran, which was in right, which was next.

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So I don't have to type in again.

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I can just press enter and it will do the same command that I did last.

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And you'll notice that when I do next, it will then print out as it will then print out this line because

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it hasn't executed it.

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Like I said, it stopped right before execution.

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So when I press the next, it will execute Line seven and then go to the next line.

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So you see that at what it did.

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Is it printed out, right?

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Printing it to the console console out, as is Hello world.

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So that's why we see Hello World print here before it now telling us that we've moved from line seven

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to line eight.

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Right.

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So another interesting thing, if you want to examine something that's in the program, you can actually

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say use the Pekerman for print.

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You can say print as well, but you can shortcut it with P.

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And so what if I want to say P and then s?

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So it tells me, like this huge thing?

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It's like, Oh, this is like some huge, huge string, you know, it's like this allocator you notice

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here it says, Hello, world here.

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But it's going to show you like a lot of stuff to do with the object in memory, so no strings.

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I don't know if I mentioned that much, but strings are objects, something that we might have not talked

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about yet in the course.

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But since it's an object, it's something that a little more complicated than just a basic data type

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is going to show all kinds of stuff here.

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But you can also see the Helloworld world right here, so you can try printing out different things.

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You might be able to print out something like this, you know, like s one, it says that it can't find

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this operator.

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So there's some things you can do, some things you can't do in GDP.

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You can kind of just experiment to see what you can do.

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We can also print out something else if I go to the next line.

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I have this into a equals four plus seven.

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So let me go to the next line, and it looks like it actually went and printed out this, either there,

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in fact.

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So I said print as sub one, it's taken off by an operator.

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But then I went to next and it actually printed out the E and Hello world.

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So if I go next again.

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No, I'm on line 10, so a has been set, so what I could do is they print a and it actually shows you

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that it's 11, right?

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Seven plus four is 11.

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So I'm able to print out a is a primitive type.

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So it didn't show like all of this information here, that it had with the string.

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So pretty cool if you want to step into something, I don't really have a function call here, but if

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you want to step into something rather than standing in for next, it's actually s first step.

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And you can, I think you can just say step as well, but it's easier to just put it in.

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So if you want to step into a function, call it just like we did in the other debugger.

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You can use the S command once you're on that line.

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So if you have stopped on a line as a function call, this is not a function call, of course.

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But if you are out of line, that's a function call.

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You could just type as to step into that function.

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So pretty cool.

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You know, there's a lot more you can do in GDB, you can actually set watch points, just like I said

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in the other debugger and.

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You know, you can reference things like pointers and all that, so it's really powerful, and if you

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would like to know more about it, just like I said with the other debugger and sea lion, I would go

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ahead and look up some documentation on GDP.

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Just scour the internet to look for some things.

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It's good practice because most of the time in your program, you're going to need to look stuff up,

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right?

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If you don't know how to do something, you'll have to look at the syntax, look up the command, et

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cetera.

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So I think it would be a good idea for you to look more into the GDP documentation to see how you can

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do some other things.

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I'm going to show you, or at least try to show you one more thing in GDP.

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So one one kind of intermediate thing is if you want to quit out and grab you, press Q and then it

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asks you if you're sure and you'll say Yes, OK, I've jumped over to bash to show you one last thing

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to do with that has to do with GDP.

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So this is basically on how to debug a segmentation fault.

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So I was just doing it in the command prompt, but.

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I was actually having a hard time creating segmentation fault, believe it or not, some of the compilers

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kind of handle things a certain way, so it's kind of sometimes hard to guarantee a segmentation fault.

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So what do we have here is a modified the test CPA file a little bit.

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You notice here I create a pointer to be and pointer.

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Important to tap into and I make it zero, so it's basically a null pointer, and then here I try and

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reference a null pointer, which is a problem.

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So that will lead to a segmentation fault.

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So if we go ahead and clear this, I have already compiled it with debug symbols.

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So I ran a command that was like this to compile it and then I'm going to run.

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It just called out and you notice it says segmentation fault.

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So segmentation fault.

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You probably already encountered some honestly yourself, but they're kind of one of the most annoying

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things because if it just if you run your program and it just says cauda, you know, horse segmentation,

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fault or whatever bad access, something like that.

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It's pretty hard, it seems pretty ambiguous for you to figure out like what's going on.

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Of course, you can go that primitive method and just put a bunch of see out statements to see how far

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your program actually makes it when it runs before it crashes.

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But there is a kind of more straightforward way of solving these problems, and that is using GDP.

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So we'll use GDP again with this eight out sound of GDP eight, out nine and bash.

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So I'll go ahead and run this.

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And then what I'm going to do is just straight up press run our four run.

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And you notice it says program received Signal Sigue SAG, which is a segmentation fault that says here

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and it says where it actually received the signal is said B equals seven.

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You're like, huh?

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OK.

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You know, that's interesting, I wonder what's going on with this of tell you the line, this problem,

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and then you can kind of go back and look at the code and see where B is coming from.

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You know, what is B?

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Why is it not OK to D reference B and have it be seven?

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You also can use a need function called backtrace, which you can actually type out the word backtrace,

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or you can just put b t and that will show you where it came from.

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But all we came from as far as a function call was made.

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So we don't really have functions to back trace into, but we could make an example of that.

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So let's go ahead and let's go ahead and see.

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See what happens when we only do that, so I'm going to go ahead and go into here.

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I can make another function.

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We also can change this to, you know, explicitly.

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So I'll just put some other function here.

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Just call try something like that and I'll just say,

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see out.

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00:15:02,250 --> 00:15:05,490
Well, let's actually just put this stuff in here, so I'll say.

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We made this point, right?

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There's no point here, so let's go ahead and make it into winter here, so to say endpoint.

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And he and we'll just say people seven and do that, so I'll get rid of this line and then down here,

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I'll just say that we call my.

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So it's hard to say so.

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Just save my funk and we'll pass, be here.

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And then, yeah, let's just let's just save that, so I'm going to clear this and then.

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We'll go ahead and run this command again to compile it.

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And then we can do the TV out, or actually let's go ahead and just run again, just to be sure that

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it safe.

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So now it prints Hello World any, and then it's also like, Oh gosh, where's the snowfall coming from?

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So we can run TV out and we will run it again, and it will segue fault here.

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And so shows us what the signal is on.

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But we're kind of like, Oh, why is this a problem?

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You know what if we list like, Oh, here's our function here, and it just so happens that we can see

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what he was set to right now because the list just happened to get this last line in here.

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But you might not have seen this if it was far further down in the code.

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Maybe you wouldn't see and be in star vehicles, you know?

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And so what you could do is just say backtrace.

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So we've backtrace here and it shows us that we came from Maine and it just tells us exactly where we

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came from in the main function that got us to where we were here.

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So the call from my phone specifically, so it says where we last came from was in Maine, the main

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function at Test IACP and 15.

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So if I actually list right here, I mean, this is not something that you might normally do to see

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this line, but I'm just going to list because it's right there.

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But you can see blatantly why I'm here on Line 15 that I closed my phone and that was the call that

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led us to jump into my thumb.

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So you can actually, you know, back Trace is tracing back in the code to see where you came from,

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so you can figure out what the problem was.

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And of course, you know, we have this null pointer as got passed here and went up to there.

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But then that kind of helps you to, you know, if you know where you came from, you can just trace

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back and you can keep kind of running it and checking it again and testing out the values and seeing

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what the problem is.

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All right, so that's actually all I really have for debugging, so hopefully this was enough to get

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you going and help you get through some of the errors that you might have had.

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I felt like this was an important video to show because it's not immediately obvious how to debug things

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from now on, and you have a couple of tools to be able to debug.

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And of course, there are others, you know, I'm not going to show debug your have all the IDs, but

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you might be using another idea that has a nice built-in debugger.

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So of course, you know, I would implore you to look at the documentation for that specific debugger

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that your specific ID that you're using.

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All right, cool.

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So with that, I'll see you in the next lecture.