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

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() = 7

pc->sum() equals to (*pc).sum() :
pc->sum() = 7
(*pc).sum() = 7

pc_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 code
C c = new C(5,6);
// java code

// C++ code
C c(5,6);

or
C *pc;
pc = new C(5,6);

or
C *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