{"id":2233,"date":"2025-02-06T23:51:44","date_gmt":"2025-02-06T23:51:44","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=2233"},"modified":"2025-02-07T22:13:46","modified_gmt":"2025-02-07T22:13:46","slug":"namespaces","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/namespaces\/","title":{"rendered":"Namespaces"},"content":{"rendered":"\n

<\/span>What’s the Problem?<\/span><\/h2>\n\n\n\n

Imagine that you’re working with two libraries provided by different organizations. Those two organizations don’t know anything about each other (or at least, are not making any assumptions), and they don’t know anything about your code, either.<\/p>\n\n\n\n

Each of those libraries contain a function with the same name – a name conflict. How can you work with those libraries and still call either of the specified functions? This is where namespaces<\/em> come in, in C++. If you’re familiar with Java, you’ll know about Java packages<\/em>, which solve the same problem for that language.<\/p>\n\n\n\n

<\/span>Example<\/span><\/h3>\n\n\n\n

Imagine that you’re supporting an application that needs to return information about a country:<\/p>\n\n\n\n

<\/div>\n\n\n\n
\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  Countries.hpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Countries_hpp<\/span><\/span>\n#define<\/span> Countries_hpp<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><string><\/span><\/span>\n<\/span>\nconst<\/span> <\/span>std<\/span>::<\/span>string<\/span>&<\/span> <\/span>getCountry<\/span>();<\/span><\/span>\nconst<\/span> <\/span>std<\/span>::<\/span>string<\/span>&<\/span> <\/span>getCapitalCity<\/span>();<\/span><\/span>\nconst<\/span> <\/span>std<\/span>::<\/span>string<\/span>&<\/span> <\/span>getCurrencySymbol<\/span>();<\/span><\/span>\n<\/span>\n#endif<\/span> \/* Countries_hpp *\/<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  Countries.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"Countries.hpp"<\/span><\/span>\n<\/span>\nconst<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCountry<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>country<\/span> = <\/span>"England"<\/span>;<\/span><\/span>\n  <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n}<\/span><\/span>\nconst<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCapitalCity<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>capital<\/span> = <\/span>"London"<\/span>;<\/span><\/span>\n  <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\nconst<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCurrencySymbol<\/span>()<\/span><\/span>\n{<\/span><\/span>\n  <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>symbol<\/span> = <\/span>"\u00a3"<\/span>;<\/span><\/span>\n  <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
Here’s a main program that uses the Countries code:<\/p>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <<\/span>iostream<\/span>><\/span><\/span>\n#<\/span>include<\/span> <\/span>"Countries.hpp"<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> * <\/span>argv<\/span>[]) <\/span><\/span>\n{<\/span><\/span>\n  std::<\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n            << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n            << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n  std::<\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n            << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n  <\/span><\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
It outputs the following:<\/p>\n\n\n\n
The capital of England is London
Its currency is \u00a3
Program ended with exit code: 0<\/p>\n<\/div>\n<\/div>\n\n\n\n
Now, what if you wanted to have the same functionality, but you’re obtaining your code from different countries, say, England and France?<\/p>\n\n\n\n
Let’s use namespaces to do this:<\/p>\n\n\n\n
\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  England.hpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> England_hpp<\/span><\/span>\n#define<\/span> England_hpp<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><string><\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>England<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>&<\/span> <\/span>getCountry<\/span>();<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>&<\/span> <\/span>getCapitalCity<\/span>();<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>&<\/span> <\/span>getCurrencySymbol<\/span>();<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n#endif<\/span> \/* England_hpp *\/<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  England.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"England.hpp"<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>England<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCountry<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>country<\/span> = <\/span>"England"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCapitalCity<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>capital<\/span> = <\/span>"London"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCurrencySymbol<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>symbol<\/span> = <\/span>"\u00a3"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  France.hpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>ifndef<\/span> <\/span>France_hpp<\/span><\/span>\n#<\/span>define<\/span> <\/span>France_hpp<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <<\/span>string<\/span>><\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>France<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCountry<\/span>();<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCapitalCity<\/span>();<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCurrencySymbol<\/span>();<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n#<\/span>endif<\/span> <\/span>\/* France_hpp *\/<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  France.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"France.hpp"<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>France<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCountry<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>country<\/span> = <\/span>"France"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCapitalCity<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>capital<\/span> = <\/span>"Paris"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span>& <\/span>getCurrencySymbol<\/span>()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>symbol<\/span> = <\/span>"\u20ac"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
\n
\n
Here’s a main program that uses the above code:<\/p>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <<\/span>iostream<\/span>><\/span><\/span>\n#<\/span>include<\/span> <\/span>"England.hpp"<\/span><\/span>\n#<\/span>include<\/span> <\/span>"France.hpp"<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> * <\/span>argv<\/span>[])<\/span><\/span>\n{<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>using<\/span> <\/span>namespace<\/span> England;<\/span><\/span>\n    <\/span><\/span>\n    std::<\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n              << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n              << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    std::<\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n              << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  {<\/span><\/span>\n    <\/span>using<\/span> <\/span>namespace<\/span> France;<\/span><\/span>\n    <\/span><\/span>\n    std::<\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n              << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n              << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    std::<\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n              << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
It outputs the following:<\/p>\n\n\n\n
The capital of England is London
Its currency is \u00a3
The capital of France is Paris
Its currency is \u20ac
Program ended with exit code: 0<\/p>\n<\/div>\n<\/div>\n\n\n\n
<\/span>Defining a Namespace<\/span><\/h3>\n\n\n\n
You define a namespace using the following syntax:<\/p>\n\n\n\n
namespace namespace_name<\/em> \n{\n  \/\/ code declarations\n  \/\/ methods\/functions\n  \/\/ classes\n}<\/strong> \/\/ Note: no semicolon<\/code><\/pre>\n\n\n\n
(See examples in the code above.)<\/p>\n\n\n\n
<\/span>Specifying the Use of a Namespace<\/span><\/h3>\n\n\n\n
You can specify that you are referring to an entity defined within a namespace by prefixing that entity name as follows:<\/p>\n\n\n\n
namespace_name<\/em>::entity_name<\/em><\/strong><\/code><\/pre>\n\n\n\n
For example, in the above code, std::cout<\/strong> and std::string<\/strong> indicate that cout<\/strong> and string<\/strong> are defined in the std<\/strong> namespace used in the C++ Standard Library (see later for more details).<\/p>\n\n\n\n
<\/span>Using Directive<\/span><\/h3>\n\n\n\n
It is usually more convenient to use a using directive to specify that a whole scope of code is subject to the use of a namespace:<\/p>\n\n\n\n
using namespace namespace_name<\/em>;<\/strong><\/code><\/pre>\n\n\n\n
(See examples in the code above.)<\/p>\n\n\n\n
Names introduced in a using directive obey normal scope rules. The name is visible from the point of the using directive to the end of the scope in which the directive is found. Entities with the same name defined in an outer scope are hidden.<\/p>\n\n\n\n
<\/span>Having Multiple Namespaces in Scope Simultaneously<\/span><\/h3>\n\n\n\n
It is possible — probably a common occurrence — to have more than one namespace currently in scope.<\/p>\n\n\n\n
Let’s change the above code to show how that can be done. I’ve removed all the explicit std::<\/strong> prefixes from the above code, and instead use suitably located using namespace declarations:<\/p>\n\n\n\n
\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  England.hpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> England_hpp<\/span><\/span>\n#define<\/span> England_hpp<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><string><\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> <\/span>std<\/span>;<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>England<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>&<\/span> <\/span>getCountry<\/span>();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>&<\/span> <\/span>getCapitalCity<\/span>();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>&<\/span> <\/span>getCurrencySymbol<\/span>();<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n#endif<\/span> \/* England_hpp *\/<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  England.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"England.hpp"<\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> std;<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>England<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCountry()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span>& country = <\/span>"England"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> capital = <\/span>"London"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> symbol = <\/span>"\u00a3"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  France.hpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>ifndef<\/span> <\/span>France_hpp<\/span><\/span>\n#<\/span>define<\/span> <\/span>France_hpp<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <<\/span>string<\/span>><\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> std;<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>France<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCountry();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol();<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n#<\/span>endif<\/span> <\/span>\/* France_hpp *\/<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  France.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"France.hpp"<\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> std;<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>France<\/span><\/span>\n{<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCountry()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span>& country = <\/span>"France"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> capital = <\/span>"Paris"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol()<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> symbol = <\/span>"\u20ac"<\/span>;<\/span><\/span>\n    <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
\n
\n
Here’s the modified main program that uses the above code:<\/p>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <<\/span>iostream<\/span>><\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> std;<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"England.hpp"<\/span><\/span>\n#<\/span>include<\/span> <\/span>"France.hpp"<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> * <\/span>argv<\/span>[])<\/span><\/span>\n{<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>using<\/span> <\/span>namespace<\/span> England;<\/span><\/span>\n    <\/span><\/span>\n    <\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n              << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n              << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    <\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n              << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  {<\/span><\/span>\n    <\/span>using<\/span> <\/span>namespace<\/span> France;<\/span><\/span>\n    <\/span><\/span>\n    <\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n         << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n         << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    <\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n         << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
Its output is the same as before:<\/p>\n\n\n\n
The capital of England is London
Its currency is \u00a3
The capital of France is Paris
Its currency is \u20ac
Program ended with exit code: 0<\/p>\n<\/div>\n<\/div>\n\n\n\n
<\/span>Nested Namespaces<\/span><\/h3>\n\n\n\n
Namespaces may be nested:<\/p>\n\n\n\n
\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  UK.hpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>ifndef<\/span> <\/span>UK_hpp<\/span><\/span>\n#<\/span>define<\/span> <\/span>UK_hpp<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <<\/span>string<\/span>><\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> std;<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>UK<\/span><\/span>\n{<\/span><\/span>\n  <\/span>namespace<\/span> <\/span>England<\/span><\/span>\n  {<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCountry();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol();<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>namespace<\/span> <\/span>Scotland<\/span><\/span>\n  {<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCountry();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol();<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>namespace<\/span> <\/span>Wales<\/span><\/span>\n  {<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCountry();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol();<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>namespace<\/span> <\/span>NorthernIreland<\/span><\/span>\n  {<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCountry();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity();<\/span><\/span>\n  <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol();<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n#<\/span>endif<\/span> <\/span>\/* UK_hpp *\/<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  UK.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"UK.hpp"<\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> std;<\/span><\/span>\n<\/span>\nnamespace<\/span> <\/span>UK<\/span><\/span>\n{<\/span><\/span>\n  <\/span>namespace<\/span> <\/span>England<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCountry()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span>& country = <\/span>"England"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> capital = <\/span>"London"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n<\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> symbol = <\/span>"\u00a3"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>namespace<\/span> <\/span>Scotland<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCountry()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span>& country = <\/span>"Scotland"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> capital = <\/span>"Edinburgh"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n<\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> symbol = <\/span>"\u00a3"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>namespace<\/span> <\/span>Wales<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCountry()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span>& country = <\/span>"Wales"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> capital = <\/span>"Cardiff"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n<\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> symbol = <\/span>"\u00a3"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>namespace<\/span> <\/span>NorthernIreland<\/span><\/span>\n  {<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCountry()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span>& country = <\/span>"Northern Ireland"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>country<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCapitalCity()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> capital = <\/span>"Belfast"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>capital<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span><\/span>\n    <\/span>const<\/span> <\/span>string<\/span>& getCurrencySymbol()<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>static<\/span> <\/span>const<\/span> <\/span>string<\/span> symbol = <\/span>"\u00a3"<\/span>;<\/span><\/span>\n      <\/span>return<\/span> <\/span>symbol<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
And here’s a main program that uses the above code:<\/p>\n\n\n\n
\n
\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  Namespaces<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 2\/7\/25.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <<\/span>iostream<\/span>><\/span><\/span>\n<\/span>\nusing<\/span> <\/span>namespace<\/span> std;<\/span><\/span>\n<\/span>\n#<\/span>include<\/span> <\/span>"UK.hpp"<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> * <\/span>argv<\/span>[])<\/span><\/span>\n{<\/span><\/span>\n  <\/span>using<\/span> <\/span>namespace<\/span> UK;<\/span><\/span>\n  {<\/span><\/span>\n    {<\/span><\/span>\n      <\/span>using<\/span> <\/span>namespace<\/span> England;<\/span><\/span>\n      <\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n           << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n           << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n           << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span><\/span>\n    {<\/span><\/span>\n      <\/span>using<\/span> <\/span>namespace<\/span> Scotland;<\/span><\/span>\n      <\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n           << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n           << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n           << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span><\/span>\n    {<\/span><\/span>\n      <\/span>using<\/span> <\/span>namespace<\/span> Wales;<\/span><\/span>\n      <\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n           << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n           << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n           << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n    <\/span><\/span>\n    {<\/span><\/span>\n      <\/span>using<\/span> <\/span>namespace<\/span> NorthernIreland;<\/span><\/span>\n      <\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"The capital of "<\/span><\/span>\n           << <\/span>getCountry<\/span>() << <\/span>" is "<\/span><\/span>\n           << <\/span>getCapitalCity<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n      <\/span>cout<\/span> << <\/span>"Its currency is "<\/span><\/span>\n           << <\/span>getCurrencySymbol<\/span>() << std::<\/span>endl<\/span>;<\/span><\/span>\n    }<\/span><\/span>\n  }<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
\n
It outputs the following:<\/p>\n\n\n\n
The capital of England is London
Its currency is \u00a3
The capital of Scotland is Edinburgh
Its currency is \u00a3
The capital of Wales is Cardiff
Its currency is \u00a3
The capital of Northern Ireland is Belfast
Its currency is \u00a3
Program ended with exit code: 0<\/p>\n<\/div>\n<\/div>\n\n\n\n
<\/span>Summary<\/span><\/h2>\n\n\n\n
The above examples are just simple examples. If you wanted to do this in the real world, you wouldn’t do it this way. There is far too much duplicate code. But I hope it conveys the idea and functionality of namespaces.<\/p>\n","protected":false},"excerpt":{"rendered":"
What’s the Problem? Imagine that you’re working with two libraries provided by different organizations. Those two organizations don’t know anything about each other (or at least, are not making any assumptions), and they don’t know anything about your code, either. Each of those libraries contain a function with the same name – a name conflict. […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":910,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-2233","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2233","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/comments?post=2233"}],"version-history":[{"count":5,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2233\/revisions"}],"predecessor-version":[{"id":2241,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/2233\/revisions\/2241"}],"up":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/910"}],"wp:attachment":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/media?parent=2233"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}