用VS2010编写C++程序，释放内存出错

Question

#include "stdafx.h"

#include "string"

#include "iostream"

using namespace std;

#define NUM 100

class MyString

{

private:

string *m_data;

public:

MyString(){m_data=new string;}

MyString(string a){m_data=new string(a);}

~MyString(){delete m_data;}                                    

 /* 如果不写delete则没有错误，写上则出现 “Unhandled exception at 0x53681f68(msvcp100d.dll), 0xC0000005:Access violation reading location 0xfeeefeee.*/

MyString(MyString &s){m_data=new string(*s.m_data);}

MyString operator + (MyString s);

void show();

};

MyString MyString::operator+(MyString s)

{

string a,b,c;

a=*m_data;

b=*(s.m_data);

c=a+b;

return MyString(c);

}

void MyString::show()

{

cout<<*m_data<<endl;

}

int main()

{

string a,b;

cout<<"请分别输入两个字符串："<<endl;

cin>>a>>b;

MyString S1(a),S2(b),S3;

S3=S1+S2;

S3.show();

int s;

cin>>s;

return 1;

}

Answer 1

#include "stdafx.h"
#include "string"
#include "iostream"
using namespace std;
#define NUM 100
class MyString
{
private:
 string *m_data;
public:
 MyString(){m_data=new string;}
 MyString(string a){m_data=new string(a);}
 ~MyString(){delete m_data;}                                   
 /* 如果不写delete则没有错误，写上则出现Unhandled exception at 0x53681f68(msvcp100d.dll), 0xC0000005:Access violation reading location 0xfeeefeee.*/
 MyString(MyString &s){m_data=new string(*s.m_data);}
 MyString* operator + (MyString s);
 void show();
};
MyString* MyString::operator+(MyString s)
{
 string a,b,c;
 a=*m_data;
 b=*(s.m_data);
 c=a+b;
 return new MyString(c);
}
void MyString::show()
{
 cout<<*m_data<<endl;
}
int main()
{
 string a,b;
 cout<<"请分别输入两个字符串:"<<endl;
 cin>>a>>b;
 MyString S1(a),S2(b),*S3;
 S3=S1+S2;
 S3->show();
 delete S3;
 S3 = NULL;
 int s;
 cin>>s;
 return 1;
}

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Visual C++ enthusiast, like network programming and driver development. At present is being engaged in the WinCE/Windows Mobile platform embedded development.

Answer 2

错误的原因是什么呢？不明白。

Answer 3

缺少等号运算法重载

S3=S1+S2;

这里会调用operator = 但是没有所以进行浅层拷贝。导致临时变量中早已把S3的m_data释放了。

const MyString& opertaor=(const MyString& r)

{

    if(this == &r)

{

   return *this;

}

else

{

deletet m_data;

m_data=new string(*r.m_data);

}
}

你也可以尝试使用COW，现在看代码优化的地方比较多。

 

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麻烦把正确答案设为解答。