C++之7|转换函数

执行出现段错误是因为出现异常却没设法去捕获异常而造成的。这时候需要用到异常处理（之前所学内容例29），修改如下

#include 
#include 
#include 

using namespace std;

class A{
public:
	virtual void show()
	{
		cout<<"aaaaaaa"<
public:
	void show()
	{
		cout<<"bbbbbbbbbbbbaaaaaaa"<
	try{

		A a;	
		B &p = dynamic_cast( a );
	}
	catch(bad_cast e)
	{
		cout< 
这时候编译虽然警告，但最后能够成功执行
 
@ubuntu:/mnt/hgfs/ub2$ g++ cast9.cpp 
cast9.cpp: In function ‘int main()’:
cast9.cpp:29:31: warning: dynamic_cast of ‘A a’ to ‘class B&’ can never succeed
   B &p = dynamic_cast( a );
                               ^
@ubuntu:/mnt/hgfs/ub2$ ./a.out
std::bad_cast
@ubuntu:/mnt/hgfs/ub2$ 

 
2、自定义转换函数 
例34、operator 
#include 
#include 
#include 

using namespace std;

class Timer{
public:
	Timer()
	{
		hour = 0;
		min = 0;
		sec = 0;
	}
	~Timer()
	{

	}

	void addtimer(int sec=1)
	{
		this->min += (this->sec+sec)/60;
		this->sec = (this->sec+sec)%60;
	}

	void show()
	{
		printf("%2d:%2d:%2dn", hour, min, sec);
	}

	Timer operator+(int sec)
	{
		Timer tem;
		tem.sec = this->sec+sec;
		return tem;
	}
	Timer operator+(Timer &x)
	{
		Timer tem;
		tem.sec = sec+x.sec;
		tem.min = min+x.min;
		tem.hour = hour+x.hour;
		return tem;
	}

	Timer operator++(int)
	{
		Timer tem = *this;//backup
	
		sec++;

		return tem;
	}

	Timer operator++()
	{
		sec++;
		return *this;
	}

	bool operator==(Timer &x)
	{
		if(sec==x.sec && min==x.min && hour==x.hour)
			return true;
		return false;
	}

	int &operator[](int i)
	{
		switch(i)
		{
		case 0: 
			return hour;
		case 1: 
			return min;
		case 2: 
			return sec;
		}
	}
//转换成int就operator int()
	operator int()
	{
        //实现相应的功能，此处是转成秒
		return sec+min*60+hour*60*60;
	}

	friend ostream &operator<<(ostream &out, const Timer &t);
private:
	int hour;
	int min;
	int sec;
};

ostream &operator<<(ostream &out, const Timer &t)
{
	out << "hour: "<
	Timer t;
	t.addtimer(3);

	int sec = t;	//强转为整形类型
	
	cout<< sec < 
3、隐式构造 
例35、explicit 
#include 

using namespace std;

class mempool{
public:
	//构造函数
	//mempool(int size){
	//explicit隐式构造
	explicit mempool(int size){
		data = new char[size];	
		cout<< "cccccccccc" <
		delete [] data;
	}

private:
	char *data;
};

int main()
{
	//调用构造函数
//	mempool a(100);
	//在平常构造函数时无法去识别下式子是赋值100还是表示a大小为100，使用explicit隐式构造可以报错区分
	mempool a = 100;
}

 
错误提示
 
@ubuntu:/mnt/hgfs/ub2$ g++ mempool.cpp 
mempool.cpp: In function ‘int main()’:
mempool.cpp:28:14: error: conversion from ‘int’ to non-scalar type ‘mempool’ requested
  mempool a = 100;
              ^~~
@ubuntu:/mnt/hgfs/ub2$