面向对象程序设计-C++ Stream & Template & Exception【第十五次上课笔记】

/*************************************************************************
    > File Name: Code09.cpp
    > Author: Jeremy Wu
    > Created Time: Mon 08 Jun 2015 09:55:51 AM CST
 ************************************************************************/

//跟字符串相关的流：1）支持C风格的字符串流
//                    2）支持C++风格的字符串流
//    1 )    strstream (istrstrstream,    ostrstream)
//    2 )    stringstream (istringstream, ostringstream)

#include <iostream>
#include <sstream>    
#include <string>

using namespace std;

float str_to_float (const char * s) {
    istrstream tmp (s, strlen (s));
    float ans;
    tmp >> ans;
    return ans;
}

int main () {

    //想把整数输入到字符串里
    
    ostringstream oss;
    int i = 123;
    double d = 1.414;

    oss << i << ‘\t‘ <<d;
    string str = oss.str ();
    
    cout << str << endl;

    //C++ 字符串

    istringstream iss ("223 2.414");
    iss >> i >> d;
    cout << i << ‘\t‘<< d << endl;
    
    //C 字符串

    char *s = "v  -3.1 // 3.1415";
    

    return 0;
}

/*************************************************************************
    > File Name: Code07.cpp
    > Author: Jeremy Wu
    > Created Time: Mon 08 Jun 2015 09:46:45 AM CST
 ************************************************************************/

//流的输入输出的格式化
// 控制格式两种方式 1）使用 setfs 等控制符
//                    2）cout 的时候使用操作值

#include <iostream>

using namespace std;

//ios 是所有流的基类

ios::fmtflags oldFlag = cout.flags ();

int main () {

    int i = 47;
    cout.setf (ios::showpos);    //显示正负号
    cout << i << endl;
    cout.setf (ios::showbase);    //显示进制号    
    //16进制输出
    cout << hex << i << endl;
    //8进制输出
    cout << oct << i << endl << endl;
    
    cout.flags (oldFlag);

    //默认保留6位数字
    double f = 1234.56789;
    cout << "default: \t" << f << endl;
    
    //科学计数法，默认保留小数后6位数字
    cout.setf (ios::scientific, ios::floatfield);
    cout << "scientific: \t" << f << endl;
                                                    
    //固定点模式，默认保留小数后6位数字
    cout.setf (ios::fixed, ios::floatfield);
    cout << "fixed: \t " << f << endl;

    //恢复默认值
    cout.setf (ios::fmtflags (0), ios::floatfield);
    cout << "default: \t" << f << endl << endl;
    
    //输出浮点数默认精度
    cout << "default precision is " << cout.precision () << endl;

    //修改默认精度
    cout.precision (8);

    cout << "after precision (8)" << endl;
    cout << "default: \t" << f << endl;
    
    cout.setf (ios::scientific, ios::floatfield);
    cout << "scientific: \t" << f << endl;

    cout.setf (ios::fixed, ios::floatfield);
    cout << "fixed: \t" << f << endl << endl;

    cout.flags (oldFlag);

    //输出预留宽度        
    cout << "Current width: \t" << cout.width ()
        << "\t Currend fill character : \t" << cout.fill () << endl;
    
    cout.precision (6);

    //设置预留宽度
    //设置填充为 # 
    //默认按右边对齐
    //
    //    ·修改 width 只针对下一次输出有效
    //
    cout.width (20);
    cout.fill (‘#‘);

    cout << f << endl;
    
    cout << "Current width: \t" << cout.width ()
        << "\t Currend fill character : \t" << cout.fill () << endl;

    cout << f << endl << endl;

    cout.width (20);
    cout << -f << endl;
    cout.width (20);

    //左边对齐
    cout.setf (ios::left, ios::adjustfield);
    cout << -f << endl;
    cout.width (20);
    
    //中间对齐
    cout.setf (ios::internal, ios::adjustfield);
    cout << -f << endl << endl;

    cout.flags (oldFlag);

    return 0;
}

/*************************************************************************
    > File Name: Code08.cpp
    > Author: Jeremy Wu
    > Created Time: Mon 08 Jun 2015 09:51:33 AM CST
 ************************************************************************/

//函数模板
//实例化的真正含义： 函数模板 -> 模板函数

#include <iostream>
#include <cstring>

using namespace std;

/*
int sum (int a, int b) {
    return a + b;
}

double sum (double a, double b) {
    return a + b;
}
*/

//模板的定义
template <typename T>    //template head
T sum (T _a, T _b) {
    return _a + _b;
}

//模板变量和模板常量（可以提供默认值
template <typename T = double, int Size = 45>
class Array {
private:
    //const static int Size = 100;
    T a[Size];
public:
    Array () { memset (a, 0, sizeof (a)); }
    T & operator [] (int index);
    Array & operator + (T rhs) {
        for (int i = 0; i < Size; ++i) a[i] += rhs;
        return *this;
    }
};

//在类的外部定义的时候
//    1）加模板头
//    2）类后面加 <T>
template <typename T, int Size>
T & Array <T, Size>::operator [] (int index) {
    if (index < 0 || index >= Size) {
        cout << "out of range" << endl;
        //exit (0);
    } else {
        return a[index];
    }

}

int main () {
    
    //模板的实例化 : 显示实例化 和 隐示实例化
    /*
    int i (10), j (7);
    cout << sum (i, j) << endl;

    double d1 (12.3), d2 (7.9);
    cout << sum <int> (d1, d2) << endl;
    */

    //Array <double, 100> ay;
    Array <>ay;
    ay[41] = 42;
    cout << ay[41] << endl;

    ay = ay + 5.2;
    cout << ay[41] << endl;

    return 0;
}

/*************************************************************************
    > File Name: Code10.cpp
    > Author: Jeremy Wu
    > Created Time: Mon 08 Jun 2015 11:44:31 AM CST
 ************************************************************************/

//异常处理: exception handling
//try \ throw \ catch
//要理解异常处理的执行顺序

#include <iostream>
#include <string>

using namespace std;

class ExcepClass {
public:
    string message () { return "devide number is invalid"; }
};

double devide (int a, int b) {
    if (0 == b)    throw ExcepClass ();    //如果符合条件，函数结束，所有局部变量释放
    cout << "Just after throw" << endl;
    return double (a) / b;
}

int main () {

    cout << "Before exception" << endl;

    try {
        int i (80), j (0);
        cout << devide (i, j) << endl;
        
        //出现异常以后的所有代码都不会被执行
        cout << "After devide (i, j)" << endl;
    }
    
    catch (ExcepClass k) {    //类型必须匹配捕捉到的类型
        cout << k.message () << endl;
    }
    
    catch (int m) {

    }
    catch (...) {    //捕捉任何类型的异常,并且...必须放在最后
        cout << "Captur all exception" << endl;
    }
    
    //结束异常处理
    cout << "After capture processing" << endl;

    return 0;
}