C++，如果类中存在指针形式的成员变量， 默认赋值运算符在析构的过程中，可能会出现删除已经删除的数据（行为），导致程序异常终止。

解决方式：重载赋值运算符，进行深度复制，demo如下：

strng.h

#include<iostream>

#ifndef STRNG_H
#define STRNG_H

class StringBad
{
public:
	StringBad(const char *s);
	StringBad();
	~StringBad();
	
	StringBad &operator=(const StringBad &st);
	
private:
	char *str;
	int len;
	static int num_strings;
	
};


#endif //STRNG_H

Strng.cpp

#include <cstring>
#include "strngbad.h"

using std::cout;

int StringBad::num_strings = 0;

StringBad::StringBad(const char *s)
{
	len = std::strlen(s);
	str = new char[len + 1];
	std::strcpy(str, s);
	num_strings++;
	std::cout << num_strings << ":\"" << str
	          << "\" object created\n";
}

StringBad::StringBad()
{
	len = 4;
	str = new char[4];
	std::strcpy(str, "C++");
	num_string++;
	std::cout << num_strings << ": \"" << str
	          << "\" default object created\n";
}

StringBad::~StringBad()
{
	std::cout << "\"" << str << "\" object deleted,";
	--num_strings;
	std::cout << num_string << "left\n";
	delete[] str;
}

StringBad &StringBad::operator=(const StringBad &st)
{
	if(this == &st){
		return *this;
	}
	delete[] str;
	len = st.len;
	str = new char[len + 1];
	std::strcpy(str, st.str);
	return *this;
}

main.cpp

#include <iostream>
#include "strng.h"

using namespace std;

int main()
{
	StringBad src("abcde");
	StringBad dest;
	dest = src;
	return 0;
}