C++之用程序理解浅拷贝

C++中的浅拷贝是产生很多问题的根本原因，其根本原因是在有指针的时候，只是拷贝了一个指针的值，多个指针指向同一块内存区域，当free内存时，造成其他指针指向的空间不存在。结合构造函数和析构函数理解浅拷贝是一个不错的选择

原始程序

#include "iostream"
using namespace std;class Name
{
public:
Name(const char *pname)
{
size = strlen(pname);
pName = (char *)malloc(size + 1);
strcpy(pName, pname);
}
~Name()
{
cout<<"开始析构"<<endl;
if (pName!=NULL)
{
free(pName);
pName = NULL;
size = 0;
}
}protected:
private:
char *pName;
int size;
};void playObj()
{
Name obj1("obj1.....");
}
void main()
{
playObj();
system("pause");
}

对象的初始化

使用对象的初始化时候，会调用copy构造函数，在copy构造函数中进行深拷贝

#include "iostream"
using namespace std;class Name
{
public:
Name(const char *pname)
{
size = strlen(pname);
pName = (char *)malloc(size + 1);
strcpy(pName, pname);
}
    Name(Name &obj)
{
//用obj来初始化自己
pName = (char *)malloc(obj.size + 1);
strcpy(pName, obj.pName);
size = obj.size;
}
~Name()
{
cout<<"开始析构"<<endl;
if (pName!=NULL)
{
free(pName);
pName = NULL;
size = 0;
}
}protected:
private:
char *pName;
int size;
};void playObj()
{
Name obj1("obj1.....");
    Name obj2 = obj1; //obj2创建并初始化
}
void main()
{
playObj();
system("pause");
}

对象的=操作

在对象的=操作的时候，也是浅拷贝，此时需要使用运算符重载来解决问题

#include "iostream"
using namespace std;class Name
{
public:
Name(const char *pname)
{
size = strlen(pname);
pName = (char *)malloc(size + 1);
strcpy(pName, pname);
}
    Name(Name &obj)
{
//用obj来初始化自己
pName = (char *)malloc(obj.size + 1);
strcpy(pName, obj.pName);
size = obj.size;
}
~Name()
{
cout<<"开始析构"<<endl;
if (pName!=NULL)
{
free(pName);
pName = NULL;
size = 0;
}
}
    void operator=(Name &obj3)
{
//用obj3来=自己
pName = (char *)malloc(obj3.size + 1);
strcpy(pName, obj3.pName);
size = obj3.size;
}protected:
private:
char *pName;
int size;
};void playObj()
{
Name obj1("obj1.....");
    Name obj2 = obj1; //obj2创建并初始化
    Name obj3("obj3...");
    obj2 = obj3;
}
void main()
{
playObj();
system("pause");
}

上面程序存在的问题

在以上程序中，存在内存泄漏，obj2的指针重新指向的时候，原来的内存没有释放

#include "iostream"
using namespace std;class Name
{
public:
Name(const char *pname)
{
size = strlen(pname);
pName = (char *)malloc(size + 1);
strcpy(pName, pname);
}
    Name(Name &obj)
{
//用obj来初始化自己
pName = (char *)malloc(obj.size + 1);
strcpy(pName, obj.pName);
size = obj.size;
}
~Name()
{
cout<<"开始析构"<<endl;
if (pName!=NULL)
{
free(pName);
pName = NULL;
size = 0;
}
}
    void operator=(Name &obj3)
{
if (pName != NULL)
{
free(pName);
pName = NULL;
size = 0;
}
//用obj3来=自己
pName = (char *)malloc(obj3.size + 1);
strcpy(pName, obj3.pName);
size = obj3.size;
}protected:
private:
char *pName;
int size;
};void playObj()
{
Name obj1("obj1.....");
    Name obj2 = obj1; //obj2创建并初始化
    Name obj3("obj3...");
    obj2 = obj3;
}
void main()
{
playObj();
system("pause");
}