Thread: the operator "="error in class "String"

Code:

#include <iostream>
using namespace std;
class String
{
public:
	String(const char *str = NULL); // 通用构造函数
	String(const String &another); // 拷贝构造函数
	~ String(); // 析构函数
	String& operator =(const String&);// 赋值函数
	friend ostream& operator << (ostream&, const String& s);
	friend istream& operator>>(istream& in, String& s);
	friend String& operator+(const String&,const String&);
private:
	char *m_data; // 用于保存字符串
};
String::String(const char *str)
{
   if (str == NULL)
      m_data = NULL;
   else
   {
	   m_data = new char[strlen(str)+1];
       strcpy(m_data,str);
   }

}
String::String(const String &another)
{
   m_data = new char[strlen(another.m_data)+1];
   strcpy(m_data,another.m_data);
}
String::~String()
{
	if(m_data != NULL)
	{
		delete m_data;
		m_data = NULL;
	}
}
String & String::operator=(const String &rhs)
{
  if (*(this->m_data) == *rhs.m_data)
      return *this/*rhs*/;
  if(this->m_data!=NULL)
  this->~String();
  m_data = new char[strlen(rhs.m_data)+1];
  strcpy(m_data,rhs.m_data); 
  return *this;
}
ostream& operator << (ostream& out, const String& s)
{
  if(s.m_data)
   out << s.m_data << endl;
  return out;
}
istream& operator>>(istream& in, String& s)
{
	char *s1 = new char[1000];
   in >> s1;
   s.m_data = new char[strlen(s1)+1];
   strcpy(s.m_data,s1); 
   return in;
}
String& operator+(const String& lhs,const String&rhs)
{
  String ret(lhs);
  strcat(ret.m_data,rhs.m_data);
  return ret;
}
int main()
{
   String s ;
   cin >> s;
   String s1;
   cin >> s1;
   String s2= s+s1;//this sentence has question , but i don't know why
   cout << s2;
}

who can explain it to me ?thanks!

Originally Posted by Elysia

>> char *s1 = new char[1000];
>> in >> s1;
Never do this. You can get a buffer overrun.
Read into a std::string with std::getline or use I/O manipulators to limit the length of data to read.
.

Wouldn't using std::string defeat the purpose of making a string class in the first place? ....
If it is an exercise; he won't probably be allowed to use std::string ..

Originally Posted by manasij7479

Wouldn't using std::string defeat the purpose of making a string class in the first place? ....
If it is an exercise; he won't probably be allowed to use std::string ..

if don't use std::string ,how to write ?

Originally Posted by whiteflags

I explained in my post so you probably want to read the thread. All you need to do to know about std::setw and see examples is look it up. If you cannot use manipulators, and cannot use std::string, then the best you could do is not use operator>> for this, and instead use the istream::get() function.

ok！thank you！