#include<iostream>

using namespace std;

/**
 * C++const關鍵字和指標的結合使用
 * 1,指標常量:可以修改指標變數指向地址的值,不能修改指標變數的指向(即可以給*p賦值, 不能給p賦值)
 * 語法: dataType *const pointerVariableName = &variableName;
 * 2,常量的指標:不可以修改指標變數指向地址的值,能修改指標變數的指向(即可以給p賦值, 不能給*p賦值)
 * 語法: const dataType *pointerVariableName = &variableName;
 * 3,指向常量的指標常量:不可以修改指標變數指向地址的值,也不能修改指標變數的指向(即不可以給p賦值, 不能給*p賦值)
 * 語法: const dataType *const pointerVariableName = &variableName;
 
 
*/
int main() {
    int a = 10;
    int b = 20;
    //pointer constant
    int *const constP = &a;
    cout << "Before assignment again for value of variable which is pointed at pointer constant constP is " << *constP
         << endl;
    *constP = 100;
    cout << "After assignment again for value of variable which is pointed at pointer constant constP is 
 
" << *constP
         << endl;
    //constP = &b;
    //error: assignment of read-only variable 'constP'

    //constant's pointer
    const int *poc = &b;
    cout
            << "Before assignment again for constant's pointer poc, the value of constant which is point at constant's pointer is 
 
"
            << *poc << endl;
    poc = &a;
    cout
            << "After assignment again for constant's pointer poc, the value of constant which is point at constant's pointer is "
            << *poc << endl;
    //*poc = 100;
    //error: assignment of read-only location '* poc'

    //pointer constant's pointer
    const int *const constPoc = &b;
    //constPoc = &a;
    //error: assignment of read-only variable 'constPoc'
    //*constPoc = 100;
    //error: assignment of read-only location '*(const int*)constPoc'
    system("pause");

    return 0;
}

如何理解和記憶/區分指標常量和常量的指標?

看const關鍵字修飾的是什麼

形如:int *const p = &a;明顯const修飾的是變數p,變數p是什麼變數呢?

指標變數,即指標變數的值不能修改,而指標變數的值是地址,不能改變地址即不能改變指標變數的指向,即該指標變數是常量,故稱為指標常量

形如:const int *p = &a;明顯const修飾的變數*p,變數*p是什麼變數呢?

指向整型變數的指標p指向的變數,即一個整型變數,整型變數*p不能被修改即不能改變整型變數*p的值,即整型變數*p是個常量,故指標p被稱為指向常量的指標