String 类的实现

#include "stdafx.h"
#include <iostream>
using namespace std;

class MyString
{
public:
 MyString(const char *str = NULL);   //通用拷贝构造函数
 MyString(const MyString &another);  //拷贝构造函数
 ~MyString();  //析构函数
 MyString& operator = (const MyString&); //赋值函数

 friend ostream& operator << (ostream&, const MyString& s);
 friend istream& operator >> (istream& in, MyString& s);
 friend MyString operator + (const MyString&, const MyString&);
 bool operator == (const MyString&);
private:
 char* m_data;  //用于保存字符串
};

MyString::MyString(const char *str )
{
 if ( NULL==str )
  m_data = NULL;
 else
 {
  m_data = new char[strlen(str)+1];
  strcpy(m_data,str);
 }
}

MyString::MyString(const MyString &another)
{
 m_data = new char[strlen(another.m_data)+1];
 strcpy(m_data,another.m_data);
}

MyString::~MyString()
{
 if( m_data != NULL )
 {
  delete []m_data;
  m_data = NULL;
 }
}

MyString& MyString::operator=(const MyString& rhs)
{
 if( this == &rhs)
  return *this;
 delete []m_data;
 m_data = NULL;
 m_data = new char[strlen(rhs.m_data)+1];
 strcpy(m_data, rhs.m_data);
 return *this;
}

ostream& operator << (ostream& out, const MyString& s)
{
 if (s.m_data)
  out<<s.m_data<<endl;
 return out;
}

istream& operator >> (istream& in, MyString& s)
{
 char q[1000];
 in>>q;
 s.m_data = new char[strlen(q)+1];
 strcpy(s.m_data, q);
 return in;
}

MyString operator+(const MyString& lhs, const MyString& rhs)
{
 MyString *ret = new MyString(lhs);
 strcat(ret->m_data, rhs.m_data);
 return *ret;
}

int _tmain(int argc, _TCHAR* argv[])
{
 MyString s;
 cin >> s;
 MyString s1;
 cin >> s1;
 MyString s2 = s+s1;
 cout << s2;

 return 0;
}

 

 

有可能你在使用 strcpy 的时候 会碰到这个错误：（VS2012碰到的）

error C4996: 'strcpy': This function or variable may be unsafe. Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
1>         

d:microsoftvisiostudiovs2012_ult_enusetupvcincludestring.h(110) : see declaration of 'strcpy'

 

没关系：这个问题的解决方式是这样的

右键项目-》“Properties”-》“C/C++”-》“Preprocessor”

在Preprocessor Definitions 中添加 _CRT_SECURE_NO_WARNINGS 即可解决这个问题