[C++ Primer Plus] 第9章、内存模型和名称空间（一）程序清单

程序清单9.9（静态存储连续性、无链接性）

#include<iostream>
using namespace std;
 
const int Size=;
void strcount(const char *str){//const表示str指针不能修改指向的内容（不过可以指向另外一块内容）
    static int total=;//static静态变量，首次初始化后，其值一直存在（即第二次调用strcount函数时，total的值不会再次初始化）
    int count=;
    cout<<"\""<<str<<"\" contains ";
    while (*str++)//先判断*str是否为NULL，然后再str++
        count++;
    total+=count;
    cout<<count<<" characters\n";
    cout<<total<<" characters total!\n";
}
 
void main() {
    char in[Size];
    char next;
    cout<<"Enter a line:"<<endl;
    cin.get(in,Size);//最多接收Size-1个字符+1个'\0'
    while (cin)    // ==while(!cin.fail()),即读入流成功
    {
        cin.get(next);
        while(next!='\n')    //若next不是换行符
            cin.get(next);
        strcount(in);
        cout<<"Enter next line (empty line to quit):\n";
        cin.get(in,Size);
    }
    cout<<"Bye!"<<endl;
    system("pause");
}

程序清单9.10（常规new和定位new运算符）

 #include<iostream>
 #include<new>    //定位new运算符
 using namespace std;
 
 const int BUF=;
 const int N=;
 char buff[BUF];
 
 void main() {
     double *p1,*p2;
     int i;
     cout<<"Calling"<<endl;
     p1=new double[N];//常规new：p1是double指针
     p2=new (buff) double[N];//定位new运算符：将数组p2放在了数组buff中
     for (i = ; i < N; i++)
         p2[i]=p1[i]=+20.0*i;
     cout<<"Memory addresses:"<<endl<<" heap: "<<p1<<" static: "<<(void *)buff<<endl;//buffer是char指针，所以要使用(void *)对buffer进行强转，否则将显示字符串
     cout<<"Memory contents:"<<endl;
     for (i = ; i < N; i++)
     {
         cout<<p1[i]<<" at "<<&p1[i]<<";";
         cout<<p2[i]<<" at "<<&p2[i]<<endl;
     }
 
     cout<<"\nCalling new"<<endl;
     double *p3,*p4;
     p3=new double[N];
     p4=new (buff) double[N];
     for (i = ; i < N; i++)
         p4[i]=p3[i]=+40.0*i;
     cout<<"Memory contents:"<<endl;
     for (i = ; i < N; i++)
     {
         cout<<p3[i]<<" at "<<&p3[i]<<";";
         cout<<p4[i]<<" at "<<&p4[i]<<endl;
     }
 
     cout<<"\nCalling new third"<<endl;
     delete [] p1;
     p1=new double [N];
     p2=new (buff+N*sizeof(double)) double[N];
     for (i = ; i < N; i++)
         p2[i]=p1[i]=+60.0*i;
     cout<<"Memory contents:"<<endl;
     for (i = ; i < N; i++)
     {
         cout<<p1[i]<<" at "<<&p1[i]<<";";
         cout<<p2[i]<<" at "<<&p2[i]<<endl;
     }
     //buff指定的内存是静态内存，所以不能delete
     delete [] p1;
     delete [] p3;
 
     system("pause");
 }

程序清单9.11-13（名称空间示例）

namesp.h　　头文件

#include<string>
namespace pers{        //包含Person结构的定义和两个函数原型
    struct Person{
        std::string fname;
        std::string lname;
    };
    void getPerson(Person &);//引用
    void showPerson(const Person &);
}
 
namespace debts{    //定义Debt结构，用于存储人名和金额，使用using编译指令，让pers中的名称在debts空间也能使用
    using namespace pers;
    struct Debt{
        Person name;
        double amount;
    };
    void getDebt(Debt &);
    void showDebt(const Debt &);
    double sumDebts(const Debt ar[],int n);
}

namesp.cpp　　函数定义

#include<iostream>
#include<string>
#include "namesp.h"//自己编写的头文件只能使用引号"",系统自带的头文件使用<>,不过""也能用
 
namespace pers{
    using std::cout;
    using std::cin;
    void getPerson(Person &rp){
        cout<<"Enter first name:";
        cin>>rp.fname;
        cout<<"Enter last name:";
        cin>>rp.lname;
    }
    void showPerson(const Person &rp){
        cout<<rp.lname<<","<<rp.fname;
    }
}
 
namespace debts{
    void getDebt(Debt &rd){
        getPerson(rd.name);
        std::cout<<"Enter debt:";
        std::cin>>rd.amount;
    }
    void showDebt(const Debt &rd){
        showPerson(rd.name);
        std::cout<<": $"<<rd.amount<<std::endl;
    }
    double sumDebts(const Debt ar[],int n){
        double total=;
        for (int i = ; i < n; i++)
            total+=ar[i].amount;
        return total;
    }
}

main.cpp　　主函数

#include<iostream>
#include "namesp.h"
using std::cout;
using std::endl;
 
void other(){
    using namespace debts;
    Person dg={"Doodles","Glister"};
    showPerson(dg);
    cout<<endl;//因为showPerson没有换行
    Debt zippy[];
    int i;
    for (i = ; i < ; i++)
        getDebt(zippy[i]);
    for (i = ; i < ; i++)
        showDebt(zippy[i]);
    cout<<"Total debt: $"<<sumDebts(zippy,)<<endl;
}
 
void another(){
    using pers::Person;
    Person collector={"Milo","Rightshift"};
    pers::showPerson(collector);
    cout<<endl;
}
 
void main(){
    using debts::Debt;
    using debts::showDebt;
    Debt golf={{"Benny","Goatsniff"},120.0};
    showDebt(golf);
    other();
    another();
    system("pause");
}