Scope
Definition: A scope is a valid identifier in the program area of the body.
Category: 1; Function prototype scope
2: local scope
3: class scope
4: namespace scope
1; function prototype scope; in the function prototype declaration parameter range of action is the function prototype scope.
eg:
double area(double radius);Identifier radius range of action between the left and right brackets in the parameter list of the function area, but can not be referenced in other places.
2; the local scope: the function parameter list scope parameter, the parameter declarations from the beginning of the list, to the far end of the entire body of the function. Board has
eg；
#include<iostream>
using namespace std;
int main()
{
int a,b,t,j;
cin>>a>>b;
t=a+b;
if(a>0)
{
int c;
cin>>c;
j=a+c;
}
cout<<"t的值为"<<t<<" "<<"j的值为"<<j<<endl;
} We can see from the above a, b, t, j scope entire main function, however, if c is inside the scope.
3; class scope: class can be seen as a collection of well-known member of the class having m members of class X scope.
There are three ways to access the m:
1; if no local scope identifier declared with the same name in the member functions X, then the function can directly access the members m.
eg；
Date date;
date.show();2: The xm or expression X :: m.
eg:
void Date::show()
{
cout<<Date::day<<endl;
}3: Such expression by ptr-> m, wherein X ptr to point to an object pointer to the class.
eg;
Date*date = new date();
date->show();
4; namespace scope: a namespace identifies a namespace scope, all the statements within the namespace does not belong to the scope of the respective identifier of the front, are in namespace scoping.
Namespace effect; eliminate errors due to the same name can occur between the various modules and functions caused by type.
The following is a namespace scope of several forms of usage;
1; can refer directly to the current namespace identifier declared inside a namespace, if you need to reference other namespace identifier,
:: namespace name identifier name
eg:
namespace SomeNs{
class SomeClass{....};
}2; If you feel namespace qualified is too long, you can use the using statement
using命名空间名：：标识符名；using namespace：：标识符名；3; allows nested namespace
eg:
namespace OuterNs{
namespace InnerNs{
class SomeClass{....};
}
}Examples of verification; the following global variables declared to have global scope of space, they are valid throughout the document.
#include<iostream>
using namespace std;
int i; //在全局命名空间中的全局变量
namespace Ns {
int j; //在Ns空间中命名的全局变量
}
int main()
{
i = 5; //为全局变量i赋值
Ns::j = 6; //为全局变量j赋值
{ //子块1
using namespace Ns; //使得在当前块中可以直接引用Ns命名空间的标识符
int i; //局部变量，局部作用域
i = 7;
cout << "i=" << i << endl; //输出7
cout << "j=" << j << endl; //输出6
```
}
cout << "i=" << i << endl; //输出5
return 0;
}