C++基础复习

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);1void 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