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‫Hello and welcome this lecture.

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‫We're going to be looking at how we can write things to the output log and specifically how we can write

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‫the values of our variables into it that can help us debug our games.

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‫Let's dive in and see how this works.

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‫So in Blueprint we were able to write things to the screen when we wanted to quickly display some information

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‫or potentially to just debug something in the past.

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‫We have in C++ used a new property to do that, but we can actually do this using a log statement and

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‫it's a little bit complicated, unreal, which is why I've shied away from doing it until this point.

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‫So we're a bit more familiar with the C++ syntax before introducing it to you.

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‫Now, the way it works is if you've got the extension here, installed the unreal four snippets by caps

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‫and caps, this actually gets a little bit easier because you don't have to remember all of the complexity

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‫of the syntax.

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‫You just type, you log, and it will pop up with an IntelliSense dialog like this saying you log to

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‫help you write out the whole piece of code and you can hit, enter or select it with your mouse.

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‫And then what you're going to see is it's written out something that looks a bit like a function.

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‫It's not actually a function under the hood.

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‫It's got some a little bit of unreal magic going on here, but it's essentially a bit like a function.

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‫So what we're going to do here is we're passing in a couple of arguments to this function.

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‫The first one tells us what type of log category we are doing.

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‫The second one tells us the level of the log.

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‫So how urgent it is essentially.

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‫And then finally we have got this thing here, which is basically a function within a function which

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‫tells us the text that we need to print out.

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‫So how does this work?

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‫If we just leave this in our code, go over into unreal hit compile, we want to see where does it show

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‫up?

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‫Well, once the compilation has finished, we're going to go ahead and hit play.

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‫And what you're actually looking for is it's not going to be up on the screen here.

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‫It's going to be in the output.

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‫Log down here and you can see it just about here.

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‫It's saying, display your message and we've got how many messages?

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‫One, two, three, four, five.

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‫The reason for this is it's displaying the message for every single actor in our scene that is a moving

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‫platform.

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‫CP So that is why we're getting so many messages.

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‫And you can see we can change out the message to be whatever we wanted it to be here.

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‫And we could also put some more information into this message, such as the start location or the name

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‫of the actor, things like that.

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‫So here we go.

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‫So we've got an output log, we've got our message, and you can start to see what the categories I

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‫was talking about are.

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‫You can see we've got log temp here, but up above we've got log audio log audio mixer Log World.

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‫So there are different categories of logging that help us distinguish where is this message coming from?

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‫Which part of Unreal is this coming from?

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‫But log temp is mostly what we're going to use because it's just a temporary place for logging out debug

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‫messages and then there's display.

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‫This is the default level, log level, but we can have messages, be a bunch of different things.

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‫It can be display or any value from this table down here.

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‫So you see display here prints a message to the console and the log file.

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‫We've got the log down here which prints a message only to the log file and doesn't display it in the

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‫console.

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‫So this is for things where you don't really want it to show up so much, but might want to use it for

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‫debugging.

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‫If you're debugging someone's game and it ran on their machine, they're sending you a log file.

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‫Then you've got warning.

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‫This is for when things seem to be going wrong and it prints it to the log console and it is also in

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‫yellow.

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‫Then we've got error that prints it in red and then fatal, basically prints to the console and crashes

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‫the engine.

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‫So you kind of want to use this one as a last resort, but it does allow you to have different levels

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‫in the log file.

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‫And I'll just show you what it looks like if we put in different messages here.

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‫So I'm going to copy our line for logging and I'm going to make three of them.

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‫We're going to have a display, going to have a warning, and we're going to have an error.

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‫Now, these are typically the levels that we will use.

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‫So let's go ahead and have a look and see what they look like.

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‫Let's go into Unreal, hit the compile button and let's stop and restart play.

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‫And by the way, you can bring up the output log by hitting the tilde key twice.

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‫It brings up there you go, we've got our output log and you can see we've got three sets of message,

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‫the display which is just in the plain white warning, which is in yellow.

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‫So it stands out a little bit more, an error, obviously, which stands out a lot more.

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‫Now we can add data to our log messages.

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‫I'm just going to delete the warning and error lines of the log and we can add in some.

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‫Later into this string that's going to be printed out.

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‫The way we would do this is, for example, if I wanted to print out the move distance configured for

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‫a particular platform that's fairly straightforward to do, we can say configured move distance, and

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‫that's the text that's going to show up.

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‫I'm going to put a colon in here.

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‫And remember, this is all within the double quotes to make sure that we're including in the text.

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‫And then we can use a percent sign followed by the F character.

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‫And you see that gets highlighted differently because this is what is known as a format specified here.

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‫It's something that comes from C all the way back in history.

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‫And essentially usually you do a percentage sign and then some letter you can see the different letters

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‫down here.

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‫The F corresponds to a decimal floating point and you can see an example of what the output looks like

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‫over in the example column.

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‫And there's lots of other things down here we can represent with D or I a decimal integer like so.

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‫So we're using F because we've got a floating point number.

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‫And then what we have to do is add in another argument to the E log function.

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‫So make sure that you are doing this after you've closed the brackets for this text function and instead

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‫we're putting a comma after here.

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‫So between these two brackets, it should be inside of the outer set, but outside of the inner set,

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‫if that makes sense.

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‫And then what we can do is we can pass in the value of our variable so we can do the move distance variable

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‫like so let's go over into Unreal and see this in action.

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‫I hit the compile button, close down the compile window and hit play and then hit Tilde twice to bring

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‫up the log.

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‫And you can see our configured move distances showing up for the different platforms, 505 hundred for

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‫the two moving platforms and 1500 for the three pushes that we've got in the scene.

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‫So one piece of information that might be a little bit interesting or instructive is that we've previously

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‫talked about how we overshoot or we did overshoot the distance moved, and it would be interesting to

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‫know by what kind of levels that is happening.

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‫So what we could do is we could create a float variable inside the if statement.

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‫So we know that we've currently overshot.

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‫We can say overshoot a float variable called overshoot.

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‫We're going to set it equal to the distance moved minus the move distance.

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‫So that tells us how much the overshoot was.

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‫So I'd like you to have a go at logging the overshoot variable that we just created here.

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‫So use the Yule log function.

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‫Here it is for reference at least the kind of structure that you will probably be using.

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‫You can also practice using that you log autocomplete to put it in instead and then compile and test

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‫your code and see if it works.

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‫Pause the video and have a go.

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‫Okay.

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‫Welcome back.

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‫So we're going to use the autocomplete option here.

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‫I'm just going to close down my sidebar to have a little bit more space.

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‫And then inside this, if after we've created the variable, we are going to type you log and hit enter

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‫and then we're going to leave it at display.

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‫We're going to make the text platform overshot by and then we're going to use percent F and then between

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‫these two brackets, we're going to add a new argument for the overshoot variable like so now let's

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‫head back into Unreal.

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‫I hit the compile button, close down the live coding log, hit play and double tap that tilde key.

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‫And you can see that every time the platform is turning around, it is printing out a log message and

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‫saying how many units it overshot by.

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‫You can actually see the net.

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‫A lot of cases it's overshooting by quite a few, quite a noticeable amount of units, three units or

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‫0.5 units.

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‫That's basically 0.5% to three centimeters.

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‫It's enough that over the course of your game these platforms could have been drifting.

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‫And that's great that we've implemented a fix for that already.

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‫Great stuff.

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‫So hopefully now you've got another tool in your arsenal for trying to figure out what's going on inside

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‫your code.

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‫And later on when you are feeling more confident in making your own code, trying to figure out what's

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‫not working so well.

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‫Okay, I will see you in the next lecture.