[C++学习笔记]构造器析构器与this指针

1.       构造器：类里一种特殊类型的方法。

（1）       构造器名字和它所在类名字一样。

（2）       系统会在创建某个类的新实例后立即自动调用这个类的构造器。

（3）       构造器永远不返回任何值。

#include <iostream>class Rectangle {public:unsigned width,height;//Constructor:Rectangle(unsigned x=0,unsigned y=0);void setSize(unsigned x,unsigned y);unsigned area();unsigned perimeter();bool isSquare();protected:private:};//Define the constructor:Rectangle::Rectangle(unsigned x,unsigned y){width = x;height = y;}void Rectangle::setSize(unsigned x,unsigned y){width=x;height=y;}unsigned Rectangle::area(){return (width*height);}unsigned Rectangle::perimeter(){return(width+width+height+height);}bool Rectangle::isSquare(){if (width==height){return true;}else{return false;}}int main(){unsigned width=25;unsigned height=25;//Rectangle myRectangle;//myRectangle.setSize(width,height);Rectangle myRectangle(width,height);std::cout<<"Area is: "<<myRectangle.area()<<"./n";std::cout<<"Perimeter is: "<<myRectangle.perimeter()<<"./n";std::cout<<"The rectengle ";if (myRectangle.isSquare()){std::cout<<"is also";}else{std::cout<<"is not";}std::cout<<" a square"<<"./n/n";return 0;}

2.       析构器：销毁对象

#include <iostream>#include <string>#include <fstream>class StoreQuote{public:std::string quote,speaker;std::ofstream fileOutput;StoreQuote();//Destructor~StoreQuote();void inputQuote();void inputSpeaker();bool write();};StoreQuote::StoreQuote(){fileOutput.open("quotes.txt",std::ios::app);}//Define the destructorStoreQuote::~StoreQuote(){fileOutput.close();}void StoreQuote::inputQuote(){std::getline(std::cin,quote);}void StoreQuote::inputSpeaker(){std::getline(std::cin,speaker);}bool StoreQuote::write(){if (fileOutput.is_open()){fileOutput<<quote<<"|"<<speaker<<"/n";return true;}else{return false;}}int main(){StoreQuote quote;std::cout<<"Enter a quotation(without quotation marks):/n";quote.inputQuote();std::cout<<"Enter the person to whom quotes is attributed:/n";quote.inputSpeaker();if (quote.write()){std::cout<<"Written!/n";}else{std::cout<<"The data could not be written!/n";return 1;}return 0;}

3.       this指针：代表当前对象（因为某个类并不知道你将使用什么名字去创建一个该类的对象）。用途是避免二义性，尤其在引用变量和属性的时候。使用原则：如果代码不存在二义性，就不必使用this指针。

#include <iostream>class Rectangle {public:unsigned width,height;//Constructor:Rectangle(unsigned width=0,unsigned height=0);void setSize(unsigned width,unsigned height);unsigned area();unsigned perimeter();bool isSquare();protected:private:};//Define the constructor:Rectangle::Rectangle(unsigned width,unsigned height){this->width = width;this->height = height;}void Rectangle::setSize(unsigned width,unsigned height){this->width = width;this->height = height;}unsigned Rectangle::area(){return (width*height);}unsigned Rectangle::perimeter(){return(width+width+height+height);}bool Rectangle::isSquare(){if (width==height){return true;}else{return false;}}int main(){unsigned width=25;unsigned height=25;//Rectangle myRectangle;//myRectangle.setSize(width,height);Rectangle myRectangle(width,height);std::cout<<"Area is: "<<myRectangle.area()<<"./n";std::cout<<"Perimeter is: "<<myRectangle.perimeter()<<"./n";std::cout<<"The rectengle ";if (myRectangle.isSquare()){std::cout<<"is also";}else{std::cout<<"is not";}std::cout<<" a square"<<"./n/n";return 0;}