C + + Reference

This article mainly records the reference features in C + + and summarizes the code examples and errors.

A simple reference

The reference is an attribute of C + +, and the pointer is the C language attribute. The above code results are as follows:
20
20
100
20
True
The referenced and referenced objects occupy the same memory unit and have the same address.

Pointer variable reference

For a reference, it is created with the description of which object is referenced, and will not modify the referenced object in the future. A reference is the equivalent of a variable alias.

Reference Error Example

Swap 2 strings

#include <iostream>#include<string.h>using namespacestd;voidSwapone (Char*&x,Char*&y)//reference to Pointers{    Char*temp; Temp=x; X=y; Y=temp;}voidSwaptwo (Char**x,Char**y)//Pointer to pointers{    Char*temp; Temp= *x; *x = *y; *y =temp;}voidSwapthree (Char*x,Char*y)//pointer Passing value (this method is not possible, equivalent to the value of the pass){//Some people misunderstand this because they may have used pointers to exchange 2 integers. This is still a difference.     Char*temp; Temp=x; X=y; Y=temp;}intMain () {Char*ap ="Hello";//*AP content is the content of H,*BP is H    Char*BP ="How is it ?"; cout<<"AP:"<< AP <<Endl; cout<<"BP:"<< BP <<Endl; //Swapone (AP,BP); //Swaptwo (&AP,&BP);Swapthree (AP,BP); cout<<"Swap ap,bp"<<Endl; cout<<"AP:"<< AP <<Endl; cout<<"BP:"<< BP <<Endl; return 0;}

Reference Error Example 2

#include <iostream>using namespacestd;Const floatPi=3.14f;//ConstantsfloatF//Global VariablesfloatF1 (floatR) {f= r*r*Pi; returnF;}float& F2 (floatR//return Reference{f= r*r*Pi; returnF; //the reference to the local variable returns (note the expiration date) and the system is functioning normally, but the result will be wrong.     /*float ff = f; return FF;*/}intMain () {floatF1 (float=5);//default parameter 5, you can modify the global variable f=78.5    float& F2 (float=5);//Ibid .    floatA=F1 (); //float& b=f1 ();//in the F1 () function, the value 78.1 of the global variable F is assigned to a temporary variable, temp (created implicitly by the compiler), and then the TEMP reference B is established, and an error occurs on a temp variable.    floatC=F2 (); float& D=f2 ();//instead of defining a variable, the main function uses a reference to the global variable directly. This way, in all 4 ways, the most memory-saving space.    But be aware of the validity period that it refers to. //the global variable F here must be valid longer than reference D, so it is safe. For example, a reference to a local variable is returned. D + =1.0f; cout<<"A ="<< a <<Endl; //cout<< "b =" << b <<endl;cout<<"C ="<< C <<Endl; cout<<"d ="<< D <<Endl; cout<<"f ="<< F <<Endl; return 0;}

Reference common Errors

#include <iostream>using namespacestd;classtest{ Public:    voidFConst int&Arg);Private:    intvalue;};intMain () {intA =7; Const intb =Ten; //int &c = b;//Error: B is constant, but C is not a constant reference, correct: const int &c=b;    Const int&d =A; A++; //d++;//Error, D is a constant reference, so you cannot modifytest test;    Test.f (a); cout<<"A ="<< a <<Endl; return 0;}voidTest::f (Const int&Arg) {    //arg = ten;//constants cannot be modifiedcout <<"arg ="<< Arg <<Endl; Value= -;}/** For variables of constant type, their references must also be of constant type. * For variables of a very variable type, it can be a very good amount. * However, note: You cannot use a constant reference to modify the value of a referenced variable in any situation. */

C + + Reference