C++入门（四）

try{
    // 可能抛出异常的语句
}catch(exceptionType variable){
    // 处理异常的语句
}

try{
        throw "Unknown Exception";  //抛出异常
        cout<<"This statement will not be executed."<<endl;
    }catch(const char* &e){
        cout<<e<<endl;
    }

 try{
        throw Derived();  //抛出自己的异常类型，实际上是创建一个Derived类型的匿名对象
        cout<<"This statement will not be executed."<<endl;
    }catch(int){
        cout<<"Exception type: int"<<endl;
    }catch(char *){
        cout<<"Exception type: cahr *"<<endl;
    }catch(Base){  //匹配成功（向上转型）
        cout<<"Exception type: Base"<<endl;
    }catch(Derived){
        cout<<"Exception type: Derived"<<endl;
    }
    
最终输出：Exception type: Base

try{
       throw nums;
       cout<<"This statement will not be executed."<<endl;
   }catch(const int *){
       cout<<"Exception type: const int *"<<endl;
   }

double func (char param) throw (int);
double func (char param) throw (int, char, exception);

int a = 10;
int b = a;  //拷贝
Base obj1(10, 20);
Base obj2 = obj1;  //拷贝

Array::Array(const Array &arr){  //拷贝构造函数
    this->m_len = arr.m_len;
    this->m_p = (int*)calloc( this->m_len, sizeof(int) );
    memcpy( this->m_p, arr.m_p, m_len * sizeof(int) );
}

int main(){
    //下面是正确的用法
    int m = 100;
    Complex c(12.5, 23.8);
    long n = static_cast<long>(m);  //宽转换，没有信息丢失
    char ch = static_cast<char>(m);  //窄转换，可能会丢失信息
    int *p1 = static_cast<int*>( malloc(10 * sizeof(int)) );  //将void指针转换为具体类型指针
    void *p2 = static_cast<void*>(p1);  //将具体类型指针，转换为void指针
    double real= static_cast<double>(c);  //调用类型转换函数
   
    //下面的用法是错误的
    float *p3 = static_cast<float*>(p1);  //不能在两个具体类型的指针之间进行转换
    p3 = static_cast<float*>(0X2DF9);  //不能将整数转换为指针类型
    return 0;
}

int main(){
    const int n = 100;
    int *p = const_cast<int*>(&n);
    *p = 234;
    cout<<"n = "<<n<<endl;
    cout<<"*p = "<<*p<<endl;
    return 0;
}

int main(){
    //将 char* 转换为 float*
    char str[]="http://c.biancheng.net";
    float *p1 = reinterpret_cast<float*>(str);
    cout<<*p1<<endl;
    //将 int 转换为 int*
    int *p = reinterpret_cast<int*>(100);
    //将 A* 转换为 int*
    p = reinterpret_cast<int*>(new A(25, 96));
    cout<<*p<<endl;
   
    return 0;
}

class Base{
public:
    Base(int a = 0): m_a(a){ }
    int get_a() const{ return m_a; }
    virtual void func() const { }
protected:
    int m_a;
};
class Derived: public Base{
public:
    Derived(int a = 0, int b = 0): Base(a), m_b(b){ }
    int get_b() const { return m_b; }
private:
    int m_b;
};

int main(){
    //情况①
    Derived *pd1 = new Derived(35, 78);
    Base *pb1 = dynamic_cast<Derived*>(pd1);
    cout<<"pd1 = "<<pd1<<", pb1 = "<<pb1<<endl;
    cout<<pb1->get_a()<<endl;
    pb1->func();
    //情况②
    int n = 100;
    Derived *pd2 = reinterpret_cast<Derived*>(&n);
    Base *pb2 = dynamic_cast<Base*>(pd2);
    cout<<"pd2 = "<<pd2<<", pb2 = "<<pb2<<endl;
    cout<<pb2->get_a()<<endl;  //输出一个垃圾值
    pb2->func();  //内存错误
    return 0;
}

int main(){
    A *pa = new A();
    B *pb;
    C *pc;
   
    //情况①
    pb = dynamic_cast<B*>(pa);  //向下转型失败
    if(pb == NULL){
        cout<<"Downcasting failed: A* to B*"<<endl;
    }else{
        cout<<"Downcasting successfully: A* to B*"<<endl;
        pb -> func();
    }
    pc = dynamic_cast<C*>(pa);  //向下转型失败
    if(pc == NULL){
        cout<<"Downcasting failed: A* to C*"<<endl;
    }else{
        cout<<"Downcasting successfully: A* to C*"<<endl;
        pc -> func();
    }

cout<<"dec:"<<dec<<a<<endl;  //以十进制形式输出整数
cout<<"hex:"<<hex<<a<<endl;  //以十六进制形式输出整数a
cout<<"oct:"<<setbase(8)<<a<<endl;  //以八进制形式输出整数a

运行结果如下：
input a:34↙(输入a的值)
dec:34                   (十进制形式)
hex:22                   (十六进制形式)
oct:42                   (八进制形式)
  
char *pt="China";  //pt指向字符串"China"
cout<<setw(10)<<pt<<endl;  //指定域宽为,输出字符串
cout<<setfill('*')<<setw(10)<<pt<<endl;  //指定域宽,输出字符串,空白处以'*'填充

运行结果如下：
     China               (域宽为)
*****China               (域宽为,空白处以'*'填充)

int main( )
{
   int a=21
   cout.setf(ios::showbase);//显示基数符号(0x或)
   cout<<"dec:"<<a<<endl;         //默认以十进制形式输出a
   cout.unsetf(ios::dec);         //终止十进制的格式设置
   cout.setf(ios::hex);           //设置以十六进制输出的状态
   cout<<"hex:"<<a<<endl;         //以十六进制形式输出a
   cout.unsetf(ios::hex);         //终止十六进制的格式设置
   cout.setf(ios::oct);           //设置以八进制输出的状态
   cout<<"oct:"<<a<<endl;         //以八进制形式输出a
   cout.unseft(ios::oct);
   char *pt="China";              //pt指向字符串"China"
   cout.width(10);                //指定域宽为
   cout<<pt<<endl;                //输出字符串
   cout.width(10);                //指定域宽为
   cout.fill('*');                //指定空白处以'*'填充
   cout<<pt<<endl;                //输出字符串
   double pi=22.0/7.0;            //输出pi值
   cout.setf(ios::scientific);    //指定用科学记数法输出
   cout<<"pi=";                   //输出"pi="
   cout.width(14);                //指定域宽为
   cout<<pi<<endl;                //输出pi值
   cout.unsetf(ios::scientific); //终止科学记数法状态
   cout.setf(ios::fixed);        //指定用定点形式输出
   cout.width(12);               //指定域宽为
   cout.setf(ios::showpos);      //正数输出“+”号
   cout.setf(ios::internal);     //数符出现在左侧
   cout.precision(6);            //保留位小数
   cout<<pi<<endl;               //输出pi,注意数符“+”的位置
   return 0;
}

{
   char *a="BASIC";//字符指针指向'B'
   for(int i=4;i>=0;i--)
      cout.put(*(a+i));                  //从最后一个字符开始输出
   cout.put('\n');
   return 0;
}

#include <iostream>  //也可以用#include <stdio.h>，同时不要下一行
using namespace std;
int main( )
{
   char *a="BASIC";
   for(int i=4;i>=0;i--)
      putchar(*(a+i));
   putchar('\n');
}

int main( )
{
   int c;
   cout<<"enter a sentence:"<<endl;
   while((c=cin.get())!=EOF)
      cout.put(c);
   return 0;
}

int main( )
{
   char c;
   cout<<"enter a sentence:"<<endl;
   while(cin.get(c))  //读取一个字符赋给字符变量c,如果读取成功,cin.get(c)为真
   {cout.put(c);}
   cout<<"end"<<endl;
   return 0;
}

int main( )
{
   char ch[20];
   cout<<"enter a sentence:"<<endl;
   cin.get(ch,10,'\\n');//指定换行符为终止字符
  cout<<ch<<endl;
   return 0;
}

int main( )
{
   char ch[20];
   cout<<"enter a sentence:"<<endl;
   cin>>ch;
   cout<<"The string read with cin is:"<<ch<<endl;
   cin.getline(ch,20,'/');  //读个字符或遇'/'结束
   cout<<"The second part is:"<<ch<<endl;
   cin.getline(ch,20);  //读个字符或遇'/n'结束
   cout<<"The third part is:"<<ch<<endl;
   return 0;
}

int main( )
{
   char c;
   while(!cin.eof( ))  //eof( )为假表示未遇到文件结束符
   if((c=cin.get( ))!=' ')  //检查读入的字符是否为空格字符
      cout.put(c);
   return 0;
}

int main( )
{
   char c[20];
   int ch;
   cout<<"please enter a sentence:"<<endl;
   cin.getline(c,15,'/');
   cout<<"The first part is:"<<c<<endl;
   ch=cin.peek( );  //观看当前字符
   cout<<"The next character(ASCII code) is:"<<ch<<endl;
   cin.putback(c[0]);  //将'I'插入到指针所指处
   cin.getline(c,15,'/');
   cout<<"The second part is:"<<c<<endl;
   return 0;
}

int main( )
{
   char ch[20];
   cin.get(ch,20,'/');
   cout<<"The first part is:"<<ch<<endl;
   cin.get(ch,20,'/');
   cout<<"The second part is:"<<ch<<endl;
   return 0;
}

int main( )
{
   int a[10];
   ofstream outfile("f1.dat",ios::out);//定义文件流对象,打开磁盘文件"f1.dat"
   if(!outfile)                        //如果打开失败,outfile返回值
   {
      cerr<<"open error!"<<endl;
      exit(1);
   }
   cout<<"enter 10 integer numbers:"<<endl;
   for(int i=0;i<10;i++)
   {
      cin>>a[i];
      outfile<<a[i]<<" ";
   }            //向磁盘文件"f1.dat"输出数据
   outfile.close();                   //关闭磁盘文件"f1.dat"
   return 0;
}

int main( )
{
   int a[10],max,i,order;
   //定义输入文件流对象,以输入方式打开磁盘文件f1.dat
   ifstream infile("f1.dat",ios::in|ios::nocreate);
   if(!infile)
   {
      cerr<<"open error!"<<endl;
      exit(1);
   }
   for(i=0;i<10;i++)
   {
      infile>>a[i];  //从磁盘文件读入10个整数,顺序存放在a数组中
      cout<<a[i]<<" ";  //在显示器上顺序显示10个数
   }         
   cout<<endl;
   max=a[0];
   order=0;
   for(i=1;i<10;i++)
      if(a[i]>max)
      {
         max=a[i];  //将当前最大值放在max中
         order=i;  //将当前最大值的元素序号放在order中
      }
   cout<<"max="<<max<<endl<<"order="<<order<<endl;
   infile.close();
   return 0;
}

int main( )
{
   student stud[3]={1001,"Li",78,1002,"Wang",89.5,1004,"Fun",90};
   char c[50];  //用户定义的字符数组
   ostrstream strout(c,30);  //建立输出字符串流,与数组c建立关联,缓冲区长
   for(int i=0;i<3;i++)  //向字符数组c写个学生的数据
      strout<<stud[i].num<<stud[i].name<<stud[i].score;
   strout<<ends;  //ends是C++的I/O操作符,插入一个'\\0'
   cout<<"array c:"<<c<<endl;  //显示字符数组c中的字符
}