namespaces

[Michael Andersson]

Hi!
What's the difference between

--------------- somefile.h ---------------

namespace somenamespace
{
void foo();
}

------------------------------------------

--------------- somefile.cpp ---------------

namespace somenamespace
{
void foo()
{
...
}
}

------------------------------------------


and

--------------- somefile.h ---------------

namespace somenamespace
{
void foo();
}

------------------------------------------

--------------- somefile.cpp ---------------

using namespace somenamespace;

void foo()
{
....
}

 

[Rolf Magnus]

Hi!
What's the difference between

--------------- somefile.h ---------------

namespace somenamespace
{
void foo();
}

------------------------------------------

--------------- somefile.cpp ---------------

namespace somenamespace
{
void foo()
{
...
}
}

------------------------------------------

This version of somefile.cpp defines a function named foo in namespace
somenamespace.

and

--------------- somefile.h ---------------

namespace somenamespace
{
void foo();
}

------------------------------------------

--------------- somefile.cpp ---------------

using namespace somenamespace;

void foo()
{
...
}

This version defines a function named foo in the global namespace.

 

[David T.]

Nothing is different except the first allows you to enter and exit
namespaces in the same .cpp file.

 

[Mike Wahler]

Hi!
What's the difference between

--------------- somefile.h ---------------

namespace somenamespace
{
void foo();
}

This places a declaration of function 'foo()'
in namespace 'somenamespace'.

------------------------------------------

--------------- somefile.cpp ---------------

namespace somenamespace
{
void foo()
{
...
}
}

This places the definition of function 'foo()'
in namespace 'somenamespace'.

------------------------------------------


and

--------------- somefile.h ---------------

namespace somenamespace
{
void foo();
}

This places a declaration of function 'foo()'
in namespace 'somenamespace'. (same as in your first
example).

------------------------------------------

--------------- somefile.cpp ---------------

using namespace somenamespace;

This indicates that namespace 'somenamespace' should be
searched when resolving identifiers referred from
this scope. No new identifiers are added to namespace
'somenamespace'.

void foo()
{
...
}

This defines a function 'foo()' at file scope (not in
any namespace).

So at global scope, the statement:

foo();

calls the function 'foo()' defined immediatly above.

In order to call from global scope the function 'foo()'
which you've defined inside namespace 'somenamespace',
write:


::somenamespace::foo().

You seem to be confusing between 'defining' and 'using'
a namespace.

-Mike

 

[Filipe Sousa]

This version of somefile.cpp defines a function named foo in namespace
somenamespace.

This version defines a function named foo in the global namespace.

If I have a class called MyPrivateClass in somefile.cpp that is only used
inside this file, what is the best approach?

1)
namespace somenamespace
{
class MyPrivateClass {
//...
};

void foo() {
// use MyPrivateClass
}
}

2)
namespace
{
class MyPrivateClass {
//...
};
}

namespace somenamespace
{
void foo() {
// use MyPrivateClass
}
}

3)
namespace somenamespace
{
namespace
{
class MyPrivateClass {
//...
};
}

void foo() {
// use MyPrivateClass
}
}