C++基础复习

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C++

引用

int add（int &b）
{
b=b+1;
return b;
}
int main()
{
int a=99;
printf("%d\n",add(a));
}

构造函数

#include<iostream>
using namespace std;
class Person{
private:
    char *name;
    int age;
    char *work;
public:
    Person(){cout<<"Person()"<<endl;}
    Person(char *name){
        cout<<"Person(char *name)"<<endl;
        this->name=name;
    }
   Person(char *name,int age,char *work="none"){
        cout<<"Person(char *name,int age)"<<endl;
        this->name=name;
        this->age=age;
        this->work=work;
    }
    void printfInfo(void)
    {
        cout<<"name="<<name<<" age="<<age<<" work="<<work<<endl;
    }
};
int main()
{
    Person Per("chenmiaohong",16);
    Person Per2;//调用无参数构造函数
    Person Per3();//定义了一个函数Per3();

    Person *per4=new Person;//调用无参数构造函数，创建对象的简写，与下面的写法相同
    Person *per5=new Person();//调用无参数构造函数
    Person *per6=new Person[2];
    Person *per7=new Person("ls",18,"stu");
    Person *per8=new Person("ww",16);

    Per.printfInfo();
    per7->printfInfo();
    per8->printfInfo();
    delete per4;
    delete per5;
    delete []per6;
    delete per7;
    delete per8;
    return 0;
}

析构函数

 #include<iostream>
#include<string.h>
using namespace std;
class Person{
private:
    char *name;
    int age;
    char *work;
public:
    Person(){cout<<"Person()"<<endl;
    this->work=NULL;
    this->name=NULL;
    }
    Person(char *name){
        cout<<"Person(char *name)"<<endl;
        this->name=new char[strlen(name)+1];
        strcpy(this->name,name);
        this->work=NULL;
    }
    Person(char *name,int age,char *work="none"){
        cout<<"Person(char *name,int age)"<<endl;

        this->age=age;
        this->name=new char[strlen(name)+1];
        strcpy(this->name,name);
        this->work=new char[strlen(work)+1];
        strcpy(this->work,work);
    }
    ~Person()
    {
        cout<<"~Person()"<<endl;
        if(this->name)
        {
            cout<<this->name<<"----"<<endl;
            delete this->name;
        }

        if(this->work)
        {

            delete this->work;
        }


    }
    void printfInfo(void)
    {
        cout<<"name="<<name<<" age="<<age<<" work="<<work<<endl;
    }

};

int main()
{

    Person Per("chenmiaohong",16);
    Person Per2;
    Person Per3();
    Person *per4=new Person;///调用无参数构造函数
    Person *per5=new Person();//调用无参数构造函数
    Person *per6=new Person[2];
    Person *per7=new Person("ls",18,"stu");
    Person *per8=new Person("ww",16);


    Per.printfInfo();
    per7->printfInfo();
    per8->printfInfo();
    delete per4;
    delete per5;
    delete []per6;
    delete per7;
    delete per8;
}

析构函数在对象销毁前的瞬间被调用。
Person *per7=new Person(“ls”,18,”stu”);
delete per7;
new创建的对象，必须用delete函数销毁掉，负责不会调用析构函数。
Person Per(“chenmiaohong”,16);
Person *Per7=new Person(“ls”,18,”stu”);
delete Per7;
调用~Person的顺序为先new对象被释放，接着按构造顺序相反的顺序释放，先创建的后调用析构函数。

默认拷贝构造函数
Person per(“zhangsan”,18);
Person per2(per);
调用默认的拷贝构造函数将per的值传递给per2，但是这样引入问题因为per与per2指向内存的同一块地址，当对象被销毁时，都会去释放这块内存。
拷贝构造函数实现

Person(Person &per){
        cout<<"(Person &per)"<<endl；
        this->age=per.age;
        this->name=new char[strlen(per.name)+1];
        strcpy(this->name,per.name);
        this->work=new char[strlen(per.work)+1];
        strcpy(this->work,per.work);
    }
int main()
{
    Person per("zhangsan",18);
    Person per2(per);
    per2.printfInfo();
    return 0;
}

类的静态成员

类成员必须通过类的对象来访问，不能通过类名直接访问。如果将类的成员定义为静态成员，则允许使用类名直接访问，静态成员使用static关键字访问

class Person{
public：
static unsigned int m_Price;//静态数据成员通常需要在类外部进行初始化
}
unsigned int Person::m_Price=10;
在一个类中类的静态数据成员被类中所有的类对象所共享。不论哪个对象对其值进行了修改。其他对象的静态数据成员也会被修改。
静态数据成员可以是当前类的类型，而其他数据成员只能是当前类的指针或者应用。
class Person{
public:
static unsigned int m_price;
Person per;//非法的定义，不允许在该类中定义所属类的对象
static Person per1;//正确,静态数据成员允许定义类的所属类对象
Person *per2;//正确，允许定义类的所属类型的指针型对象
}
静态数据成员可以作为成员函数的默认参数，其他数据成员不可以
class Person()
{
public:
static unsigned int m_per;
int m_page;
void OutputInfo(int data=m_per)//正确，静态数据成员作为函数的默认参数
{
cout<<data<<endl;
}
void OutputPage(int page=m_page)//错误
{
cout<<page<<endl;
}
}

类的静态成员函数只能访问静态数据成员，不能访问非静态数据成员。
static void Outputinfo()const；错误的定义，静态成员函数末尾不能使用const关键字
在类中定义的静态成员函数，在类外实现时不能添加static关键字

对象的构造顺序

构造顺序：按运行中定义对象的顺序调用构造函数，静态对象只调用一次构造函数; 全局对象在main函数执行前被构造

Person per_g("per_g",10);1
void fun()
{
    Person per_func("per_func",11);4
    static Person per_func_s("per_func_s",11);5
}
int main()
{
    Person per_main("per_main",11);2
    static Person per_main_s("per_main_s",11);3
    for(int i=0;i<2;i++)
    {
        fun();
        Person per_for("per_for",i);6
    }
    return 0;
}

析构函数调用顺序：

局部普通类对象，主函数内对象，局部static对象，main函数static对象，全局static对象

Person(char *name,int age,char *work="none"){
        cout<<"Person(char*,int),name="<<name<<",age="<<age<<endl;

        this->age=age;
        this->name=new char[strlen(name)+1];
        strcpy(this->name,name);
        this->work=new char[strlen(work)+1];
        strcpy(this->work,work);
    }
......
class Student{
private:
    Person father;
    Person mother;
    int stu_id;
public :
    Student()
    {
        cout<<"Student()"<<endl;
    }
    Student(int id,char *father,char *mother,int father_age=40,int mother_age=39):father(father,father_age),mother(mother,mother_age)使用父类的构造函数
    {
        cout<<"Student(int id,char *father,char *mother,int father_age=40,int mother_age=39)"<<endl;

    }

};
int main()
{
    Student s(10,"cath","lily");
    return 0;
}

构造函数调用顺序是：先调用father、mother、stu
析构函数调用顺序是：先调用stu、mother、father