Here's my code:
#ifndef DATE_H_
#define DATE_H_
namespace std {
class Date {
public:
Date();
virtual ~Date();
};
} /* namespace std */
#endif /* DATE_H_ */
I created class Date for my assignment, and it created
the namespace std{......}. I don't know the use of it.
why it is not written as usual use namespace std;
what is the difference?
Your code declares your class Date within the namespace std, i.e. your class fully qualified name would be std::Date
A statement
using namepace std;
Will include the namespace std when searching for symbols.
Some additional notes:
using namespace on a *.h (or anything that get included in multiple files)... because it might have unexpected side-effects with symbols resolved to wrong namespaces.
First of all: you shouldn't put anything in the std namespace, ever.
namespace foo
{
class A {};
}
puts the class A in the namespace foo, so its full name is foo::A.
using namespace foo;
means that you can access all the things that are in foo without using the qualifier foo::.
Note that using namespace is generally frowned upon and can lead to many unexpected problems.
Most importantly, don't write it in headers.
If you say
using namespace foo;
class A{};
A is not inside foo, but in the global namespace.
std::swap in the std namespace.