昨天電腦問題 補昨日8-3複習內容 異常與文件操作

1.類型轉換

c 方式 強制類型轉換過於粗暴  各種類型間可以隨意轉換 編譯器難以判斷正確性

#include <iostream>

#include <windows.h>

using namespace std;

class A
{
private:
	int m_a;
public:
	void seta(int a);
	A();

};

void A::seta(int a)
{
	m_a = a;
}

A::A()
{
	m_a = 0;
}

class B :public A
{
private:
	int m_b;
public:
	void setb(int b);
	B();

};

void B::setb(int b)
{
	m_b = b;
}

B::B()
{
	m_b = 0;
}

//c語言中的無敵強制類型轉換
//1.1c++中的普通類型轉換static_cast		是在編譯時期轉換的 運行時無法檢測類型 
//1.2c++中的強制類型轉換reinterpret_cast
//1.3c++中的常類型轉換const_cast

int main()
{
	/*1.1*/
	/*
	int a = 1;
	double b = 2.1;

	a = (int)b;
	a = static_cast<int>(b);//可以用於普通數據類型轉換

	A aa;
	B bb;

	aa = bb;
	aa = static_cast<A>(bb);//可以用於派生類數據類型轉換

	A *pa = new A;
	B *pb = new B;

	pa = pb;
	pa = static_cast<A *>(pb);//可以用於派生類指針類型轉換
	pb = static_cast<B *>(pa);

	int *cha = new int;
	double *chb = new double;

	cha = (int *)chb;
	//cha = static_cast<int *>(chb);//不可用於普通指針類型的轉換
	*/

	/*1.2*/
	/*
	int a = 1;
	char b = 'a';
	int *pa = &a;
	char *pb = &b;

	pa = reinterpret_cast<int *>(pb);
	pb = reinterpret_cast<char *>(0x100);
	*/

	/*1.3*/

	const int a = 1;
	int *pa = const_cast<int *>(&a); //const_cast作用就是去除原來的const,下面兩個一樣

	const int &b = 1;
	int &pb = const_cast<int &>(b);	//但是這裏的int & 是常引用 用常量初始化 相當於 定義了一個變量
	pb = 2;
	cout << "b is : " << b << endl;

	const int c = 1;
	int &pc = const_cast<int &>(c);	/*這裏的常 變量 用常數初始化 是將其寫在符號表中 數值不可更改 
									（和#define差不多 只是作用域不同 
									#define 作用域是那一行向下 常變量 相當於局部變量*/
	pc = 2;
	cout << "c is : " << c << endl;

	system("pause");
	return 0;
}

2.異常處理機制

發生錯誤時 就拋出問題 讓接收的 進行處理

/*簡單瞭解一下 異常處理機制*/
/* 一層拋出 */

#include <iostream>

#include <windows.h>

using namespace std;

double Div(double a, double b)
{
	if (b == 0)
	{
		throw 'a';					//除數爲0 拋出異常 
									//拋出 整型數值	catch裏面就寫	int
									//拋出 char 字符	catch裏面就寫	char
	}
	return a / b;
}

int main()
{
	double  a, b;
	cout << "please input two numbers: " << endl;

	cin >> a >> b;

	try
	{
		cout << Div(a, b) << endl;
	}
	catch (int)
	{
		cout << "(int) second number zero is error " << endl;
	}
	catch (char)
	{
		cout << "(char) second number zero is error " << endl;
	}

	system("pause");
	return 0;
}


/* 兩層 或者 多重拋出 */

#include <iostream>

#include <windows.h>

using namespace std;

double Div(double a, double b)
{
	if (b == 0)
	{
		throw 'a';					//除數爲0 拋出異常 
									//拋出 整型數值	catch裏面就寫	int
									//拋出 char 字符	catch裏面就寫	char
	}
	return a / b;
}

double f(double x, double y)
{
	try
	{
		Div(x , y);
	}
	catch (char)
	{
		throw 0;
	}
}

int main()
{
	double  a, b;
	cout << "please input two numbers: " << endl;

	cin >> a >> b;

	try
	{
		cout << f(a, b) << endl;
	}
	catch (int)
	{
		cout << "(int) second number zero is error " << endl;
	}
	catch (char)
	{
		cout << "(char) second number zero is error " << endl;
	}

	system("pause");
	return 0;
}


/* 注意如果函數聲明的時候 後面接throw() 括號裏有什麼類型 就只可以拋出什麼類型的異常 沒有就無法拋出異常 看到相應代碼要認識 */
#include <iostream>

#include <windows.h>

using namespace std;

double Div(double a, double b) throw();


double f(double x, double y)
{
	try
	{
		Div(x, y);
	}
	catch (char)
	{
		throw 0;
	}
}

int main()
{
	double  a, b;
	cout << "please input two numbers: " << endl;

	cin >> a >> b;

	try
	{
		cout << f(a, b) << endl;
	}
	catch (int)
	{
		cout << "(int) second number zero is error " << endl;
	}
	catch (char)
	{
		cout << "(char) second number zero is error " << endl;
	}

	system("pause");
	return 0;
}

double Div(double a, double b) throw()
{
	if (b == 0)
	{
		throw 'a';					//除數爲0 拋出異常 
		//拋出 整型數值	catch裏面就寫	int
		//拋出 char 字符	catch裏面就寫	char
	}
	return a / b;
}


/* 拋出異常 的過程中 創建了類對象 在對應的括號結束時 會自動析構（相當於函數體結束） */
#include <iostream>

#include <windows.h>

using namespace std;

class Test
{
private:
	int m_a;
public:
	Test();
	~Test();
};

Test::Test()
{
	cout << "Test constructor ok~ " << endl;
}

Test::~Test()
{
	cout << "Test destructor ok~ " << endl;
}

double Div(double a, double b)
{
	if (b == 0)
	{
		Test t2;

		cout << " throw under here to do (here is t2)" << endl;
		throw 'a';					//除數爲0 拋出異常 
									//拋出 整型數值	catch裏面就寫	int
									//拋出 char 字符	catch裏面就寫	char
		
	}
	return a / b;
}

int main()
{
	double  a, b;
	cout << "please input two numbers: " << endl;

	cin >> a >> b;

	try
	{
		Test t1;
		cout << Div(a, b) << endl;
		cout << "Div(a, b) func over (here is Test t1)" << endl;
	}
	catch (int)
	{
		cout << "(int) second number zero is error " << endl;
	}
	catch (char)
	{
		cout << "(char) second number zero is error " << endl;
	}

	system("pause");
	return 0;
}  


/* 如果拋出 類對象 */

#include <iostream>

#include <windows.h>

using namespace std;

class Test
{
private:
	int m_a;
public:
	Test();
	~Test();
};

Test::Test()
{
	cout << "Test constructor ok~ " << endl;
}

Test::~Test()
{
	cout << "Test destructor ok~ " << endl;
}

double Div(double a, double b)
{
	if (b == 0)
	{
		Test t2;

		cout << " throw under here to do (here is t2)" << endl;
		throw Test();					//除數爲0 拋出異常 異常類型爲 Test 
	}
	return a / b;
}

int main()
{
	double  a, b;
	cout << "please input two numbers: " << endl;

	cin >> a >> b;

	try
	{
		Test t1;
		cout << Div(a, b) << endl;
		cout << "Div(a, b) func over (here is Test t1)" << endl;
	}
	catch (Test)
	{
		cout << "(Test) second number zero is error " << endl;	//用 Test 接收 的話 最後會析構這個test 因爲這裏 的catch（test）中的test 調用了拷貝構造函數
	}
//	catch (Test &)
//	{
//		cout << "(Test &) second number zero is error " << endl;	//	一般建議用test & 進行捕獲 方便簡單 不需要析構
//	}
//	catch (Test *t)
//	{
//		cout << "(Test *t) second number zero is error " << endl;	//	test * 捕獲的話 最後要記得刪除 指針
//		delete t; //
//	}

	system("pause");
	return 0;
}

3.異常類

異常是類 – 創建自己的異常類
異常派生
異常中的數據：數據成員
按引用傳遞異常
在異常中使用虛函數
案例：設計一個數組類 MyArray，重載[]操作，
數組初始化時，對數組的個數進行有效檢查 
index<0 拋出異常eNegative  
index = 0 拋出異常 eZero  
    3）index>1000拋出異常eTooBig 
    4）index<10 拋出異常eTooSmall 
    5）eSize類是以上類的父類，實現有參數構造、並定義virtual void printErr()輸出錯誤。

#include <iostream>

#include <windows.h>

using namespace std;

class Myarray
{
private:
	int m_len;
	char *m_data;
public:
	Myarray(int l);
	~Myarray();

	class esize
	{
	protected:
		char *msg;
	public:
		esize(char *m) : msg(m)
		{

		}
		virtual void printerror() = 0;
	};

	class enegative : public esize
	{
	public:
		enegative() : esize("enegative exception")
		{
			
		}
		void printerror()
		{
			cout << msg << endl;
		}
	};

	class ezero : public esize
	{
	public:
		ezero() : esize("ezero exception")
		{
			
		}
		void printerror()
		{
			cout << msg << endl;
		}
	};

	class Toosmall : public esize
	{
	public:
		Toosmall() : esize("Toosmall exception")
		{
			
		}
		void printerror()
		{
			cout << msg << endl;
		}
	};

	class Toobig : public esize
	{
	public:
		Toobig() : esize("Toobig exception")
		{
	
		}
		void printerror()
		{
			cout << msg << endl;
		}
	};

	
};

Myarray::Myarray(int l)
{
	if (l < 0)
	{
		throw enegative();
	}
	else if (l == 0)
	{
		throw ezero();
	}
	else if (l > 0 && l <= 10)
	{
		throw Toosmall();
	}
	else if (l > 1000 )
	{
		throw Toobig();
	}
	m_len = l;
	m_data = new char[m_len + 1];
}

Myarray::~Myarray()
{
	cout << "destuct Myarray ok~ " << endl;
}

int main()
{
	try
	{
		Myarray a1(-1);
		Myarray a2(10);
		Myarray a3(0);
		Myarray a4(1001);
	}
	catch (Myarray::enegative &e)        /*上面說過的用 & 去接收； 這裏因爲是類中類 
                                                                    所以加上域限制*/
	{
		e.printerror();
	}
	catch (Myarray::Toosmall &e)
	{
		e.printerror();
	}
	catch (Myarray::Toobig &e)
	{
		e.printerror();
	}
	

	system("pause");
	return 0;
}

4.創建自己的異常類

#include <iostream>

#include <Exception>

using namespace std;

class Myexception :public exception
{
private:
	char *Errmsg;
public:
	Myexception(char *s) : Errmsg(s)
	{

	}
	virtual const char * what() const throw()
	{
		return Errmsg;
	}
};

double Div(double x , double y)
{
	if (0 == y)
	{
		throw Myexception("xxxxx");
	}
	return x / y;
}

int main()
{
	double a = 2.5, b = 0;
	try
	{
		cout << Div(a , b) << endl;
	}
	catch (Myexception &a)
	{
		cout << a.what() << endl;
	}
	
	system("pause");
	return 0;
}

5.文件操作

#include <iostream>

#include <iomanip>
#include <windows.h>

using namespace std;

int main()
{
	int a = 1314;
	cout << "十六進制 1314 : " << hex << a << endl;
	cout << "十進制 1314 : " << dec << a << endl;
	cout << "八進制 1314 : " << oct << a << endl;
	cout << "setbase(16) 1314 : " << setbase(16) << a << endl;

	system("pause");
	return 0;
}


/* 打開文件 輸入程序 */
#include <iostream>

#include <fstream>
#include <windows.h>

using namespace std;

int main()
{
	char buf[32] = {0};
	ifstream ifs("hello.txt",ios::in);		//創建文件對象 打開方式爲 讀出  從文件讀出 到 程序

	//ifs >> buf;
	//cout << "read from hello.txt :" << buf << endl;

	char ch;
	while ((ch = ifs.get()) != EOF)
	{
		cout << ch;
	}
	cout << endl;
	
	
	system("pause");
	return 0;
}


/* 打開第一個文件 將其中內容 複製到 另一個文件中 */

#include <iostream>

#include <fstream>
#include <windows.h>

using namespace std;

int main()
{
	ifstream ifs("hello.txt", ios::in); //讀取文件

	char buf[32] = {0};

	ifs.read(buf , 32);

	ofstream ofs("hello1.txt", ios::out);		//創建文件對象 打開方式爲 寫入 從程序 寫入到 文件 app方式是追加

	//char buf[32] = "xxxxxxxxxx";

	//ofs << buf;

	ofs.write(buf , 32);

	ofs.close();

	


	system("pause");
	return 0;
}