Use of namespaces

Use of namespaces
Definition of namespace
namespace nsl {
int a;
int b;
}
Namespace declaration

1.using The following namespace member names must be namespace qualified names . for example ：
using nsl:: Student;  //  Only members in one namespace can be declared at a time through this method , Declaration of subsequent Student It's a namespace nsl Medium Student.
2.using namespace nsl;  //  Through this method, all members in a namespace can be declared at one time . Only in namespace data is there little , And ensure that there are no members with the same name in these namespaces using namespace sentence .
3. Nameless namespace , Its scope is from the location where the nameless namespace is declared to the file A end . amount to static