Be careful when the pointer is deleted twice

In the C ++ class, it is sometimes used to call the passed value (Object object as a parameter). In this case, be careful! Especially when the object you pass a value has a long lifecycle rather than a temporary object (lifecycle segment. Let's take a look at the following situation:

#include <iostream>using namespace std; class Text{private:    char * str; public:    Text(){str = new char[20];::memset(str,0,20);}    void SetText(char * str)    {        strcpy(this->str,str);    }    char * GetText() const{return str;}    ~Text()    {        cout << "~Text Destruction" << endl;        delete [] str;        cout << "~Text Over" << endl;    }}; void Print(Text str){    cout << str.GetText() << endl;} int main(){    Text t;    t.SetText("abc");    Print(t);    return 1;}

The execution result program crashes. Cause:

Print (Text Str) does not perform deep copy when copying and constructing STR; when print exits, it is a temporary object (constructed at the initial time of the function ), analyze STR, and there is no flaw at this time; but return to main, and then exit main, and then analyze t, however, the content in STR in T has been destroyed. A memory error occurs because a memory space is destroyed twice.

Solution:

1. Override the shortest copy. Make appropriate adjustments in different situations like the following versions:
   

   #include <iostream>using namespace std; class Text{private:    char * str; public:    Text(){str = new char[20];::memset(str,0,20);}    Text(Text &t)    {        str = new char[20];        strcpy(str,t.GetText());    }    void SetText(char * str)    {        strcpy(this->str,str);    }    char * GetText() const{return str;}    ~Text()    {        cout << "~Text Destruction" << endl;        delete [] str;        cout << "~Text Over" << endl;    }}; void Print(Text str){    cout << str.GetText() << endl;} int main(){    Text t;    t.SetText("abc");    Print(t);    return 1;}

2. (Recommended) do not use value transfer for calling. As shown in the following print version:

   void Print(Text &str){    cout << str.GetText() << endl;}

3. Unless all the members in the object readNon-pointer memory contentSo proceed with caution.