About C + + reference variables and namespaces

One, C + + reference variables

Beginners C + + is exposed to the reference variable, defining the type as an integral type:

int A;
int &b=a;

Represents the definition of B as a reference variable, the value of a is referenced, and B is the same as the address of a, and if you change the value of B, the value of the a,b will change, but the address of the reference variable B will not change, and the reference variable is similar to the pointer, but it is different and has different characteristics. The following procedure is used as a comparative analysis:

#include <iostream>
using namespace std;
int main ()
{
	int a,b;
	int &c=a;
	int *q;
	q=&a;
	a=1;
	b=2;
	cout<<c<<endl;
	cout<<*q<<endl;
	cout<<&c<<endl;
	cout<<q<<endl;
	q=&b;
	c=b;//b=2 to C   
	cout<<a<<endl;//a into 2 
	cout<<c<<endl;
	cout<<*q<<endl;
	The address of the cout<<&c<<endl;//reference variable is not changed and remains the original address of a 
	cout<<q<<endl;
	return 0;	

Run the results as shown. This shows that the c,*q is a specific value, and &C,Q is the address value, when the Q points to B, Q's address into B's address, the value of a will not change, so that C reference B, A,c value are changed, but the address of C is still the address of a. This is the reference to the variable's related content.

Ii. about namespaces

C + + In consideration of the possibility of duplicate variables, functions, and so on, set the concept of namespaces, for example, in C + + when the use of <iostream.h>, equivalent to call the library function in C, using the global namespace, that is, the early implementation of C + +; When using < Iostream>, the header file does not define a global namespace and must use namespace Std to properly use cout.

This is the use of a using namespace STD, which refers to a standard library-related identifier, and all identifiers in the C + + standard library are defined in a namespace named Std.

At the same time, namespace can also be customized by the user, the following code to illustrate the meaning of namespace:

Displaynamespacedemonstration
#include <iostream>
using namespace std;
Namespace Savitch1 
{
    void greeting ();
}
Namespace Savitch2 
{
    void greeting ();
}
void Big_greeting ();
int main ()
{
    {
        using namespace Savitch2;
        Use SAVICTCH2, STD, global three namespaces
        greeting ();
    {
        using namespace Savitch1;
        Use SAVITCH1, STD, global three namespaces
        greeting ();
    Big_greeting ();
    Use STD and global two namespaces return
     
    0;
}
Namespace Savitch1 
{
    void greeting ()
    {
        cout<< ' hellofromnamespacesavitch1.\n ';
    }
}
namespace Savitch2 
{
    void greeting ()
    {
        cout<< "greetingsfromnamespacesavitch2.\n";
    }
}
void Big_greeting ()
{
    cout<< "abigglobalhello!\n";
}

It can also be changed to use the following:

Displaynamespacedemonstration
#include <iostream>
using namespace std;
Namespace Savitch1 
{
    void greeting ();
}
Namespace Savitch2 
{
    void greeting ();
}
void Big_greeting ();
int main ()
{
    {
        
        ///using SAVICTCH2, STD, global three namespaces
        savitch2::greeting ();
    }
    {
        
        //using SAVITCH1, STD, global three namespaces
        savitch1::greeting ();
    }
    Big_greeting ();
    Use STD and global two namespaces return
     
    0;
}
Namespace Savitch1 
{
    void greeting ()
    {
        cout<< ' hellofromnamespacesavitch1.\n ';
    }
}
namespace Savitch2 
{
    void greeting ()
    {
        cout<< "greetingsfromnamespacesavitch2.\n";
    }
}
void Big_greeting ()
{
    cout<< "abigglobalhello!\n";
}