17、C++ Primer 4th 笔记，构造函数

#include "iostream"

using namespace std;

class Sales_item {
public:
	//default argument for book is the empty string
	Sales_item(const std::string &book = ""):
	  isbn(book), units_sold(0), revenue(0.0) { }
    Sales_item(std::istream &is);
	  // as before
private:
	string isbn;
	int units_sold;
	int revenue;
};

int main()
{
	Sales_item empty;
	Sales_item Primer_3rd_Ed("0-201-82470-1");
	return 1;
}

Sales_item myobj();// oops! declares a function, not an object
//the following are right.
Sales_item myobj; //defines a class object ...
Sales_item myobj = Sales_item() //ok,create an unnamed, empty Sales_itemand use to initialize myobj

class Salse_item
{
publi:
	Salse_item(const std::string &book = ""):isbn(book)...{}
	Salse_item(std::iostream &is);
	//explicit Salse_item(std::iostream &is);

	...
	bool same_isbn(Salse_item &si)
	{
	...
	}
};

int main()
{
	Salse_item item;
	string null_book = "12345";
	item.same_isbn(null_book); //会发生自动转换，把string类型转换成Salse_item型。
	item.same_isbn(cin);  ////会发生自动转换，把cin流类型转换成Salse_item型。
	//item.same_isbn(Salse_item(null_book)); //显式的进行转换
}