#include<iostream> class MyString {   public:     MyString (const char *str=NULL);     MyString (const MyString &other);     ~ MyString(void);     MyString & operator = (const MyString & other);   private:       char *m_data; }; #include "MyString.h" using namespace std; MyString::MyString(const char *str):m_data(NULL) {     char *p = NULL;     if(str == NULL)     {         p = new char[1];         if(p == NULL)         {             //分配空间失败             cout<<"分配空间失败"<<endl;             exit(-1);         }         else         {             *p = '\0';             m_data = p;             p = NULL;         }     }     else     {         size_t length = strlen(str);         p = new char[length +1];         if(p == NULL)         {             //分配空间失败             cout<<"分配空间失败"<<endl;             exit(-1);         }         else         {             strcpy(p,str);             m_data = p;             p = NULL;         }     } } MyString::MyString (const MyString &other) {     char *p = NULL;          size_t length = strlen(other.m_data);          p = new char[length+1];     if(p == NULL)     {         //分配空间失败         cout<<"分配空间失败"<<endl;         exit(-1);     }     else     {         strcpy(p,other.m_data);         m_data = p;         p = NULL;     } } MyString::~MyString(void) {     if(m_data != NULL)     {         delete[] m_data;         m_data = NULL;     } } MyString & MyString::operator=(const MyString & other) {     if(this == &other)     {         return *this;     }     char *p = NULL;          size_t length = strlen(other.m_data);          p = new char[length+1];     if(p == NULL)     {         //分配空间失败         cout<<"分配空间失败"<<endl;         //exit(-1);         return *this;//没有修改     }     else     {         strcpy(p,other.m_data);         delete[] m_data;         m_data = p;         p = NULL;     }     return *this; }