# # #, c + + reference

A variable is a “house number” of memory, artificially named so that it can have multiple aliases, which are references.

The main function of ###### reference: as a function parameter or return value, instead of pointer, make the program readable.

  1. Simply aliasing a variable is meaningless. Passing it as a function parameter ensures that no copies are generated during parameter passing.

  2. A reference can directly manipulate a variable, while a pointer can indirectly manipulate a variable by taking the value (*p). The readability of a pointer is poor.

  3. The sizeof the reference is the same as the sizeof the type.

    #include

    using namespace std;

    void main(){

     int a = 10;
 int &b = a;

 b = 20;
 cout << b << endl;

 system("pause");
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    }

In this example, variable A and reference B essentially access the same memory address. It’s kind of like a pointer.

Examples of value swapping:

#include <iostream> using namespace std; Void swap1(int *a, int *b){int c = *a; *a = *b; *b = c; Void swap2(int &a, int &b){int c = a; a = b; b = c; } void main(){ int a = 10; int b = 20; swap1(&a, &b); swap2(a, b); cout << a << endl; cout << b << endl; // find the largest number, which is b, and then assign b to 30 //C++ tri operator can assign a > b? a : b = 30; cout << b << endl; system("pause"); }Copy the code

#### a reference to a pointer that can replace a secondary pointer

struct Teacher{
	char* name;
};

void set1(Teacher** a){
	(*a)->name = "wu";
}

void set2(Teacher* &a){
	a->name = "lu";
}

void main(){
	Teacher t;
	Teacher* p_t = &t;
	set1(&p_t);
	cout << t.name << endl;

	set2(p_t);
	cout << t.name << endl;

	system("pause");
}
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#### Pointer constants and constant Pointers

Pointer constants, pointer constants, do not change the address of the pointer, but can change what it points to:

int* const p1 = &a;
//p1 = &b;
*p1 = 30;
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Constant pointer: a pointer to a constant that can’t be changed, but can change its address

const int* p2 = &a;
p2 = &b;
//*p2 = 30;
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# # # # frequently quoted

  1. A reference must have a value, not null, for a pointer. When using Pointers, be careful not to null.

  2. Constant reference, cannot be assigned, equivalent to final.

    Void set(const int &a){// the reference must have a value. }

    void main(){

    int x = 0; // reference must have a value, cannot be NULL //int &a = NULL; Final const int a = x; // Final const int a = x; const int &b = 1; System ("pause");Copy the code

    }

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