C++ 构造函数

C++ 构造函数

C++ 中定义全局的对象，会引发该对象对应类及其父类的构造函数执行，因此可先于main() 函数执行。
如：

#include <iostream>
using namespace std;

// Base class defination
class Quote {
public:
Quote() = default;
Quote(const std::string &book, double sales_price) :
bookNo(book), price(sales_price) {
cout << "Quote constructor ..." << endl;
}

std::string isbn() const {
return bookNo;
}

virtual double net_price(std::size_t n) const {
cout << "Quote" << endl;
return n * price;
}

virtual ~Quote() {
cout << "Quote deconstructor ..." << endl;
}

private:
std::string bookNo;

protected:
double price;
};

// Derived class defination
class Bulk_quote: public Quote {
public:
Bulk_quote()= default;
//Bulk_quote(const std::string &book, double sales_price, std::size_t qty, double dis);
Bulk_quote(const std::string &book, double sales_price, std::size_t qty, double dis):min_qty(qty), discount(dis), Quote(book, sales_price) {
cout << "Bulk_quote constructor ..." << endl;
}

//	double net_price(std::size_t n) const {
//cout << "hello" << endl;
//	}
double net_price(std::size_t n) const {
cout << "Bulk_quote" << endl;
return n * price * discount;
}

~Bulk_quote() {
cout << "Bulk_quote deconstructor ..." << endl;
}

private:
std::size_t min_qty;
double discount;
};

//Quote basic_item("0-123", 10);
Bulk_quote item("0-123", 10, 3, 0.80);

int main() {
cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!
return 0;
}

运行输出：

Quote constructor ...

Bulk_quote constructor ...

!!!Hello World!!!

Bulk_quote deconstructor ...

Quote deconstructor ...