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Creating a namespace
The creation of a namespace is notably
similar to the creation of a class:
//: C10:MyLib.cpp
namespace MyLib {
// Declarations
}
int main() {} ///:~
This produces a new namespace containing
the enclosed declarations. There are significant differences from class,
struct, union and enum,
however:
- A namespace definition can
appear only at global scope, or nested within another
namespace.
- No
terminating semicolon is necessary after the closing brace of a namespace
definition.
- A
namespace definition can be “continued” over multiple header files
using a syntax that, for a class, would appear to be a redefinition:
//: C10:Header1.h
#ifndef HEADER1_H
#define HEADER1_H
namespace MyLib {
extern int x;
void f();
// ...
}
#endif // HEADER1_H ///:~
//: C10:Header2.h
#ifndef HEADER2_H
#define HEADER2_H
#include "Header1.h"
// Add more names to MyLib
namespace MyLib { // NOT a redefinition!
extern int y;
void g();
// ...
}
#endif // HEADER2_H ///:~
//: C10:Continuation.cpp
#include "Header2.h"
int main() {} ///:~
- A namespace name can be
aliased to another name, so you don’t have to type an unwieldy name
created by a library vendor:
//: C10:BobsSuperDuperLibrary.cpp
namespace BobsSuperDuperLibrary {
class Widget { /* ... */ };
class Poppit { /* ... */ };
// ...
}
// Too much to type! I’ll alias it:
namespace Bob = BobsSuperDuperLibrary;
int main() {} ///:~
- You cannot create an
instance of a namespace as you can with a
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