Re: Big Problem! How to overload operator delete?
Lighter wrote:
Big Problem! How to overload operator delete?
According to C++ standard, "A deallocation function can have more than
one parameter."(see 3.7.3.2); however, I don't know how to use an
overloaded delete operator. Let me use an example to illustrate this:
/********************************************************/
#include <new>
#include <iostream>
using namespace std;
void operator delete(void* p, const nothrow_t&)
{
cout << "Hello" << endl;
} // (1)
void operator delete(void* p, int a, int b)
{
cout << "World" << endl;
} // (2)
int main()
{
int* p = new(nothrow) int;
delete p; // This cannot render to show 'Hello' or 'World'
}
/********************************************************/
Even if I use 'delete(nothrow, p);', it cannot render to show 'Hello'
or 'World' either. My problem just lies here: Although I can write my
own operator delete, I cannot use it. As far as I know, the C++
standard doesn't give an example to illustrate the usage of delete (The
usage of new is given.).
An ugly way to do this is to use function call:
operator delete(nothrow, p); // This can render to show 'Hello'
However, I don't think this is the answer to my question. Who know the
correct one?
A delete expression can only call the default global operator delete (or
default one for the class if it is overloaded for the deleted type).
Special operator delete overloads are called when a constructor throws
an exception and when the constructor was triggered by a new expression
with arguments that match the operator delete overload.
The operator new/delete system isn't very well designed in some ways. In
your case, one option is to overload the default global new to call your
other one with some default arguments, and then have that overload write
those arguments somewhere where they can be accessed by operator delete.
e.g.
void* operator new(size_t n, int a, int b)
{
char* ret = static_cast<char*>(malloc(n + sizeof a + sizeof b));
memcpy(ret, &a, sizeof a);
memcpy(ret + sizeof a, &b, sizeof b);
return ret + sizeof a + sizeof b;
}
void* operator new(size_t n)
{
return ::operator new(n, 0, 0); //or whatever
}
void operator delete(void* p)
{
char* cp = static_cast<char*>(p);
int a, b;
memcpy(&a, cp - sizeof a - sizeof b, sizeof a);
memcpy(&b, cp - sizeof b, sizeof b);
//use a and b values
free(cp - sizeof a - sizeof b);
}
That should get you started, and allows you to, e.g., track
deallocations according to the __FILE__ and __LINE__ of the allocation call.
Tom