> For the complete documentation index, see [llms.txt](https://ezcode.gitbook.io/bnb-cpp/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ezcode.gitbook.io/bnb-cpp/basic/namespace.md).

# 이름공간(namespace)

## 이름공간(namespace)

 특정 영역에 이름을 붙여주기 위한 문법적 요소이다.\
`::` (범위지정연산자)를 이용해 접근합니다.

```cpp
#include <iostream>

namespace space {
  int num = 1;
  void func() {
    std::cout << "space의 num : " << num << std::endl;
  }
}

namespace otherSpace {
  int num = 2;
  void func() {
    std::cout << "otherSpace의 num : " << num << std::endl;
  }
}

int main(void)
{
  space::func();
  otherSpace::func();
  return 0;
}
```

## 이름공간 함수의 선언부와 정의를 구분하기 <a href="#ec-9d-b4-eb-a6-84-ea-b3-b5-ea-b0-84-ed-95-a8-ec-88-98-ec-9d-98-ec-84-a0-ec-96-b8-eb-b6-80-ec-99-80-e" id="ec-9d-b4-eb-a6-84-ea-b3-b5-ea-b0-84-ed-95-a8-ec-88-98-ec-9d-98-ec-84-a0-ec-96-b8-eb-b6-80-ec-99-80-e"></a>

```cpp
#include <iostream>

namespace space {
  int num = 1;
  void func();
}

namespace otherSpace {
  int num = 2;
  void func();
}

int main(void)
{
  space::func();
  otherSpace::func();
  return 0;
}

void space::func() {
  std::cout << "space의 num : " << num << std::endl;
}

void otherSpace::func() {
  std::cout << "otherSpace의 num : " << num << std::endl;
}
```

## 이름공간의 중첩 <a href="#ec-9d-b4-eb-a6-84-ea-b3-b5-ea-b0-84-ec-9d-98-ec-a4-91-ec-b2-a9" id="ec-9d-b4-eb-a6-84-ea-b3-b5-ea-b0-84-ec-9d-98-ec-a4-91-ec-b2-a9"></a>

```cpp
#include <iostream>

namespace space {
  void func();
  
  namespace otherSpace {
    void func();
  }
}

int main(void)
{
  space::func();
  space::otherSpace::func();
  return 0;
}

void space::func() {
  std::cout << "space의 func 호출" << std::endl;
}

void space::otherSpace::func() {
  std::cout << "space::otherSpace의 func호출" << std::endl;
}
```

## using 명령을 사용하여 이름공간 명시 <a href="#using-eb-aa-85-eb-a0-b9-ec-9d-84-ec-82-ac-ec-9a-a9-ed-95-98-ec-97-ac-ec-9d-b4-eb-a6-84-ea-b3-b5-ea-b" id="using-eb-aa-85-eb-a0-b9-ec-9d-84-ec-82-ac-ec-9a-a9-ed-95-98-ec-97-ac-ec-9d-b4-eb-a6-84-ea-b3-b5-ea-b"></a>

&#x20;`std`는 C++ 표준라이브러리의 이름공간입니다.\
지금까지 `std::cout`, `std::cin`, `std:endl` 처럼 객체에 접근할때 `::`를 써서 접근하였는데 std처럼 자주 쓰이는 것은 `using` 명령을 통행 **기본 이름공간으로 지정**할수 있습니다.

```cpp
#include <iostream>
using namespace std; // std 이름공간을 기본 이름공간으로 지정

int main(void)
{
  char name[100];
  cout << "이름을 입력하세요 : ";
  cin >> name;
  cout << name << "님 안녕하세요." << endl;
  return 0;
}
```

## ::(범위지정연산자)의 또다른 기능 <a href="#eb-b2-94-ec-9c-84-ec-a7-80-ec-a0-95-ec-97-b0-ec-82-b0-ec-9e-90-ec-9d-98-eb-98-90-eb-8b-a4-eb-a5-b8-e" id="eb-b2-94-ec-9c-84-ec-a7-80-ec-a0-95-ec-97-b0-ec-82-b0-ec-9e-90-ec-9d-98-eb-98-90-eb-8b-a4-eb-a5-b8-e"></a>

범위지정 연산자를 이용하여 전역변수에 접근할 수 있습니다.

```
#include <iostream>
using namespace std;

int val = 100; // 전역변수

int main(void)
{
  int val = 20;
  cout << val << endl; // 지역변수 출력
  cout << ::val << endl; // 전역변수 출력
  return 0;
}
```


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