[C++]C++Pointers to classes 类指针 new 与object的对比

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Code

#include <iostream>using namespace std;class C {    int one, two;    public:        C(int x, int y) : one(x), two(y) {}        int sum(void) { return one + two; }};int main(){    int a = 1, b = 2;       int *pa = &a;    int *pb = &b;       cout << "simple int pointer : ";    cout << "a + b = " << (*pa + *pb) << endl;      C c(3,4);    cout << "[C c ] is same as [int a ] [Type t] : ";    cout << "c.sum() = " << c.sum() << endl;    C *pc;    pc = &c;    cout << "pc->sum() equals to (*pc).sum() : " << endl;    cout << "pc->sum() = " << pc->sum() << endl;    cout << "(*pc).sum() = " << (*pc).sum() << endl;    C *pc_n;    pc_n = new C (5,6);    cout << "pc_n = new C( 5, 6) : " << endl;    cout << "pc_n->sum() = " << pc_n->sum() << endl;    pc = nullptr;    delete pc;    delete pc_n;    return 0;   }

Run

simple int pointer : a + b = 3[C c ] is same as [int a ] [Type t] : c.sum() = 7pc->sum() equals to (*pc).sum() :pc->sum() = 7(*pc).sum() = 7pc_n = new C( 5, 6) :pc_n->sum() = 11

Note

构造函数

C(int x, int y) : one(x), two(y) {}

class C的构造函数，接受两个整型的参量

对象创建

C c(3,4);

创建一个class C的对象c,接受整数3以及整数4作为构造函数的参数

方法调用

cout << "c.sum() = " << c.sum() << endl;Screen Output ： c.sum() = 7

很自然地就可以使用c.sum() 调用类中的函数

类指针

C *pc;pc = &c; // C c(3,4);

创建一个类的指针 取名为pc 本质就是Type *t，Class 也是一种Type，那么自然可以对c进行取出地址的操作 &，并将其值赋予pc

    cout << "pc->sum() = " << pc->sum() << endl;    cout << "(*pc).sum() = " << (*pc).sum() << endl;Screen Output：    pc->sum() = 7    (*pc).sum() = 7

pc->sum() 以及 (*pc).sum() 是两种等价的写法

new的用法

C *pc_n;pc_n = new C (5,6);

pc_n仍旧是一个类指针，但是被赋值为 new C (5,6)

Java vs C++

// java codeC c = new C(5,6);// java code// C++ codeC c(5,6);orC *pc;pc = new C(5,6);orC *pc;C c;pc = &c;// C++ code

java和C++的写法做一下区分记忆

Reference

[1] classes/Pointers to classes
http://www.cplusplus.com/doc/tutorial/classes/
[2] Comparison of Java and C++
https://en.wikipedia.org/wiki/Comparison_of_Java_and_C%2B%2B

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