calling the destructor from a friend class - c++

Question

I am using friend classes and I want to use rec's destructor when I call DeleteItem from my list class. However, there is a pointer pointing to the record that I want to delete, so I do not know how to call the destructor so it will do what I want.
Classes:
class rec
{
friend class list;
private:
char * id;
char firstname[15];
char lastname[15];
int ar[10];
rec* prev;
rec* next;
public:
void SetData ( char * id_in, char * fn, char * ln, int * ans_in);
rec( char *i, char *fn, char *ln, int *a);
rec();
void operator= (const rec& r);
rec (const rec& r);
void Print();
~rec();
};
class list
{
private:
rec* first;
rec* last;
public:
int AddItem(rec r);
int DeleteItem (char* delid);
void PrintList( int order);
int ReadData(char *inanswer, char *inkey);
int WriteData(char *answer, char *key);
list();
void operator= (list l);
private:
int CheckDuplicate(rec r);
void DeleteData();
int Count(char *filename);
};
~rec()
rec :: ~rec()
{
if (id != NULL)
{
delete [] id;
}
}
DeleteItem (Snipet)
int list :: DeleteItem(char *delid)
{
int id_counter;
rec *current = first;
while (current || current == NULL)
{
if (current == NULL)
{
return 0;
}
else
{
id_counter = strcmp(current -> id, delid);
if (id_counter != 0)
{
current = current -> next;
}
else
{
if (current == first && current != last)
{
~rec(); //Here
first = current -> next;
delete current;
first -> prev = NULL;
return 1;
}
Delete item will compile fine if I manually put in delete[] current ->id; but does this when I try to compile as is
list.cpp:292: error: no match for ‘operator~’ in ‘~rec()’
/usr/lib/gcc/x86_64-redhat-linux/4.3.0/../../../../include/c++/4.3.0/bits/ios_base.h:105: note: candidates are: std::_Ios_Fmtflags std::operator~(std::_Ios_Fmtflags)
/usr/lib/gcc/x86_64-redhat-linux/4.3.0/../../../../include/c++/4.3.0/bits/ios_base.h:145: note: std::_Ios_Openmode std::operator~(std::_Ios_Openmode)
/usr/lib/gcc/x86_64-redhat-linux/4.3.0/../../../../include/c++/4.3.0/bits/ios_base.h:183: note: std::_Ios_Iostate std::operator~(std::_Ios_Iostate)
Is it my destructor that needs to be fixed or is it something to do in DeleteItem?

Answer 1

To call a destructor, the syntax is current->~rec(), but in almost cases, you shouldn't call directly a destructor in C++. By calling delete current, the C++ will automatically call the destructor before de-allocating its memory.
In your case, as you are also using delete after calling ~rec(), your destructor will be called twice, so you will result to a double free corruption as your constructor is trying to free id memory.
Advice: To avoid using friend class, in your case, next and prev members are related to the list, and not to rec class. So your list class could have a nested decorator class that will wrap your rec class like:
class list
{
struct item {
rec* value;
rec* prev;
rec* next;
};
item * first;
item * last;
public:
// ...
};
Then the logic of your list will be well isolated from the logic of your rec class.