辨析 const指针 和 指向常量的指针

　　辨析以下几种指针p的定义。

int tmp = ;

int *p = &tmp;
const int *p = &tmp;
int const* p = &tmp;
int * const p = &tmp;
const int * const p = &tmp;
int const * const p = &tmp;

　　根据文献一，可以采用从右往左读的方式区分。

第一个为普通指针，指向普通int变量；

第二个和第三个相同，都是普通指针，指向const int型变量；

第四个是const指针，指向普通int变量；

第五个和第六个相同，都是const指针，指向const int型变量。

　　实验代码如下：

 #include <iostream>

 void test1() {
     int tmp = ;
     int *p = &tmp;
     std::cout << "test1:: p value: " << *p << std::endl;
     // *p and p are common variables.
     *p = ;  // ok
     int tmp1 = ;
     p = &tmp1;  // ok
 }

 void test2() {
     int tmp = ;
     const int *p = &tmp;
     std::cout << "test2:: p value: " << *p << std::endl;
     // *p is read-only, p is common variable.
 //    *p = 10;  // error
     int tmp1 = ;
     p = &tmp1;  // ok
 }

 // same with test2
 void test3() {
     int tmp = ;
     int const* p = &tmp;
     std::cout << "test3:: p value: " << *p << std::endl;
     // *p is read-only, p is common variable.
 //    *p = 10;  // error
     int tmp1 = ;
     p = &tmp1;  // ok
 }

 void test4() {
     int tmp = ;
     int * const p = &tmp;
     std::cout << "test4:: p value: " << *p << std::endl;
     // p is read-only, *p is common variable.
     *p = ;  // ok
 //    int tmp1 = 9;
 //    p = &tmp1;  // error
 }

 void test5() {
     const int tmp = ;
     const int * const p = &tmp;
     std::cout << "test5:: p value: " << *p << std::endl;
     // p is read-only, *p is also read-only.
 //    *p = 10;  // error
 //    int tmp1 = 9;
 //    p = &tmp1;  // error
 }

 // same with test5
 void test6() {
     const int tmp = ;
     int const * const p = &tmp;
     std::cout << "test6:: p value: " << *p << std::endl;
     // p is read-only, *p is also read-only.
 //    *p = 10;  // error
 //    int tmp1 = 9;
 //    p = &tmp1;  // error
 }

 int main() {
     std::cout << "Hello, World!" << std::endl;
     test1();
     test2();
     test3();
     test4();
     test5();
     test6();
     return ;
 }

References:

(1) https://www.cnblogs.com/bencai/p/8888760.html