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In this lecture, you will learn about the using namespaces.

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So namespaces gives you a mechanism to modularized code.

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So a namespace allows you to label your types, functions and variables with unique name so that using

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the scope resolution operator, you can give a fully qualified name.

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So the advantage is that you know exactly which item will be called.

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And the disadvantage is that using a fully qualified name, you are in effect switching of C++ arguments,

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dependent lookup mechanism for overloaded functions where the compiler will choose the function that

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has the best fit according to the arguments priced to function.

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So defining namespace is simple.

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For example, let's define a namespace here.

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Namespace you use the namespace keyword.

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You declare the types, functions and global variables with the namespace keyword here and the name

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you give it to it.

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So let's create the utilities namespace.

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Here.

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And.

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Here.

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So let's create a function in this namespace pool pool data.

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Pull data.

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Here.

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Let's make this, for example, just the comment, the quote here, and then let's add another function

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here, integer.

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Get data.

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Get data.

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Let's add another comment here, because we will fill these courts in later lectures code.

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Here.

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So as you can see here, we create a code, for example.

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Example code two and example for example, code one.

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And then you don't use this semicolon after declaring and link namespaces here.

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So now you use these symbols here.

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For example, if if utilities namespace pool data returns true, then you will get the.

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Then you create the integer number.

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Utilities get data.

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And here, let's add an example.

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We will use e.

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Variable here.

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So then the namespace declaration may just declare the functions, so in which case the actual functions

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will have to be defined elsewhere.

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So and you will need to use the qualified name here.

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Let's.

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Make it here.

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You can do this like this.

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For example, namespace.

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My professional.

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Utilities.

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Usually it's not best practice to make your variable names that long, but it's okay.

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Is just an explanatory code here.

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Then.

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And then let's go declare the functions.

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Declaring the functions.

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Here, Bull.

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Pull data.

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For data.

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And integer.

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Get data.

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As you can see, we can declare the same function names.

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Because of that, these two utilities doesn't have to do with each other, so they are in the different

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namespace so you can declare the same named functions here.

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Because they are they they don't have to interact with each other.

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So.

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Then we can create a pool here.

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For example, let's define the pool.

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But here.

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Bull utilities or not your.

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You can define this called letters.

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Defining the functions later here, defining the functions here.

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So pool utilities, as you can see, we are here to double dots here and pool data.

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And then you can write the.

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Court that the person who returns a bull from this function.

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And we can create the data after that.

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As you can see here, this is the integer.

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So integer.

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Oops, We have a problem here.

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Let's see.

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What is this?

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Cannot define or declare pull data here because the name does not enclose namespace utilities.

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As you can see, we can now use the.

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Another.

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As you can see, there is a different namespace, so we need to add here my professional utilities.

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And as you can see here, error is gone.

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So let's add another bool here.

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Not this is an integer sorry integer OC.

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My professional utilities get data.

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And code that returns an integer or in this function.

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So one use of a namespace is to version your code.

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So the first version of your code may have a side effect that is not in your functional specification

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and is technically back.

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So about some colors will use it and depend on it.

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When you update your code to fix the bug, you may decide to love to allow your colors the option to

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use the old version so that their code does not break.

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So you can do this with the namespace.

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But before that.

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I want to hear.

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Let's use only my professional code.

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So I just commented this code and you can use later here.

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And.

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Let's go within our namespace version two here.

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OC namespace My profession Utilities.

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And then let's create a version to in this namespace.

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So.

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Namespace.

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Namespace.

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V two.

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And then you can declare your function again.

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And here.

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Pull data.

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And the integer get data.

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Here.

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Integer Neave Future new feature.

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Yes.

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So now here, now colors we want to specify.

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It's actually make our new weird aversion to program.

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So this callers who want to specify aversion can call the fully qualified names for example colors could

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use.

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Here my professional functions.

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We two and here pull data.

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As you can see here, there's no problem.

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So we can use this namespace inside the namespace.

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So to use the so we can use this and newer version and utilities pull data.

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My professional utilities pull data to use the older version so we can use this is the new version version

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of our namespace and we can use the professional my.

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Officer, we have to end quote here.

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My professional utility is just the first version.

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So as you can see, we are using pull data now and let's use the pool data.

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So there are different functions in the same namespace.

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So when an item in a specific namespace calls an item in the same namespace, it does not have to use

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qualified name.

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So if the new feature here we which are here functions calls get data, it will be here.

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My professional.

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My professional.

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Utilities here.

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V to.

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Need to get data.

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Get data.

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Yes.

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And that is the cult.

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So.

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So it's important to note that to declare a namespace, you have to do the nesting manually as shown

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here.

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So let's create that an example to write the first version of the code that will call it using the namespace

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utilities.

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So C++ 11 provides a facility called an inline namespace that allows you to define a nested namespace,

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but lost the compiler to treat the items as being in the parent namespace when it performs an argument

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dependent lookup.

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So let's create an inline namespace here.

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K inline namespace.

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We won.

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We Yes, we won.

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Verizon won.

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And.

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Here.

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Pull.

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Pull data.

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Pull data and integer.

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Get data here.

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And as you can see, we have namespace V.

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Also, let's actually add before we v two.

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So we can.

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It's more readable.

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So now to call the version of data here, as you can see, we got an error here.

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Is ambiguous.

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So not to call the first version of data you can use the utilities, get data or utilities.

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We want.

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Full data.

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As you can see here, it's fixed.

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We won.

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We want.

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Get data.

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And utilities.

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We want pool data so fully qualified names can make the record difficult to read, especially if your

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code will only use one namespace.

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So to help you here you have several options.

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You can place a using statement using statement to indicate the symbols declared in the specified namespace.

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Same space can be used without a fully qualified name.

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So for example, you can use the using a namespace utilities.

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My professional.

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My professional utilities and like that.