C++引用与指针的区别

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
using namespace std;

double var = 1;
double _var = 999;

void test_1()
{
    /*指针和引用初始化的区别*/

    double* var_address = NULL;
    var_address = &var;
    cout << " var_address = " << var_address << endl;

    double& var_memory = var;
    var_memory = _var;
    var_memory = 888;
    cout << " var_memory = " << var_memory << endl;
    cout << " var_memory 等效 *var_address " << endl;
}

void test_2()
{
    const double& var_memory1 = var;
    //var_memory1 = _var;               const修饰double&后，var_memory1不能引用别的变量了
    //var_memory1 = 4;                  '写' var的内存  error

    /*没有这种语法
    double& const var_memory2 = var;       //vs2017可编过、其他编不过
    var_memory2 = _var;                    //const修饰var_memory2后，var_memory2可以引用别的变量
    var_memory2 = 4;                       // '写' var的内存  ok
    cout << " double& const var 等效 double& var" << endl;*/


    const double* var_address1 = &var;
    var_address1 = &_var;               //const修饰double*后，var_memory1可以保存别的变量地址
    //*var_address1 = 3;                '写' var  error
    double* const var_address2 = &var;
    //var_address2 = &_var;             //const修饰var_memory2后，var_memory2不能保存别的变量地址
    *var_address2 = 3;                  //'写' var  ok

    const double* const var_address3 = &var;
    //var_address3 = &_var;
    //*var_address3 = 3;
    cout << " const double& __ 等效 const double* const __" << endl;

}


void test_3()
{
    double* var_address = &var;
    double& var_memory = var;
    cout << " sizeof(var_address)->指针大小 double* 为处理器字节宽： " << sizeof(double*) << endl;
    cout << " sizeof(var_memory)->引用类型大小为本身double类型所占内存： " << sizeof(double&) << endl;
}


void test_4()
{
    double* var_address = &var;
    double** var_add_add = &var_address;  

    double& var_memory = var;
    //double&& var_mem_mem = var_memory;  error

    cout << " 存在二级指针不存在二级引用" << endl;
}

double* test_5(double* tmp)
{
    cout << " 传入地址（这块内存的地址）: " << tmp;
    *tmp = 666666;
    cout << " var值被更改：" << var ;
    return tmp;
}

double& test_6(double& tmp)
{
    cout << " 传入变量（这块内存的值）: " << tmp;
    tmp = 888888;
    cout << " var值被更改：" << var ;
    return tmp;
}

int main()
{

    /*1.指针保存的是变量的地址，而引用就是拿到这块内存（给这块内存取多一个别名）*/
    test_1();

    /*2.const指针与const引用*/
    test_2();

    /*3.sizeof()*/
    test_3();

    /*4.二级性*/
    test_4();

    /*5.传参与返回值*/
    cout << " 返回地址（这块内存的地址）：" << test_5(&var) << endl;
    cout << " 返回变量（这块内存的值）：" << test_6(var) << endl;

    cout << endl;
    system("pause");
    return 0;
}