operator= 要注意避免内存泄露（项目经验）

指针不论是指向malloc还是new分配得到的内存，一定要注意在改变指针指向之前一定要先释放旧的内存块。

class Test

{

public:

                 Test()

                {

                                 if (p != NULL)

                                {

                                                 free(p );

                                                 p = NULL ;

                                }

                                 p = (char *)malloc( sizeof(char ));

                }

                 Test(const Test & C1)

                {

                                 cout << "ooo我在进行拷贝构造" << endl;

                                 p = (char *)malloc( sizeof(char ));

                                * p = *C1 .p;

                }

                ~ Test()

                {

                                 cout << "ooo我在析构" << endl;

                                 if (p !=NULL)

                                {

                                                 free(p );

                                                 p = NULL ;

                                }

                }

                 void operator=(Test &C2)

                {

                                 if (p !=NULL)

                                {

                                                 free(p );

                                                 p = NULL ;

                                } 

                //这里很重要，A=B时，A本身已经malloc了一块内存，如果此时没有              

                  free，直接执行下面一句让p指向另一块内存，那么之前malloc出来的     

                  内存如何释放？

                                 p = (char *)malloc( sizeof(char ));

                                           *p = *C2.p;

                }

private:

                 char *p ;

};

void main ()

{

                 Test A ;

                 Test B ;

                 A = B ; //这里要注意，直接“=”的情况下不会调用拷贝构造函数，要用=重载来避免浅拷贝

}