c++ - What does Copy constructor do for dynamic allocations -

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• what rule of three? 8 answers

i curious why copy constructor important dynamic allocation of own defined class.

i implementing low-level c-string class dynamic allocations , here quick view of class

class string { private:     char * buf;     bool inbounds( int )     {         return >= 0 && < strlen(buf);     }     static int strlen(const char *src)     {         int count = 0;         while (*(src+count))             ++count;         return count;     }     static char *strcpy(char *dest, const char *src)     {         char *p = dest;         while( (*p++ = *src++));         return dest;     }     static char* strdup(const char *src)     {         char * res = new_char_array(strlen(src)+1);         strcpy(res,src);         return res;     }     static char * new_char_array(int n_bytes)     {         return new char[n_bytes];     }     static void delete_char_array( char* p)     {         delete[] p;     }  public:     /// both constructors should construct     /// string parameter s     string( const char * s = "")     {         buf = strdup(s);     }     string( string & s)     {         buf = strdup(s.buf);     }     void reverse()     {     }     void print( ostream & out )     {         out << buf;     }     ~string()     {         delete_char_array(buf);     } }; ostream & operator << ( ostream & out, string str ) {     str.print(out);     return out; } 

i know part of strdup() function not correct doing tests.

my problem if not have copy constructor , main()

int main() {     string b("abc");     string a(b);     cout << b << endl;     return 0; } 

the compiler tell me double free or corruption (fasttop) , find answers question , see big 3 rules.

can guys tell me why code works without errors if have copy constructor , error of double free or corruption (fasttop) means?

if don't define copy constructor, compiler insert 1 you. default copy constructor copy data members, both instances of string point same area of memory. buf variable hold same value in each instance.

therefore when instances go out of scope , destroyed, both attempt release same area of memory, , cause error.