I have a problem using a C++ map to store pointers to a base class and some derived class.
Let me explain by a rather long but simple code:
#include <map>
#include <iostream>
struct foo{ int dummy[4]; };
struct bar{ int additionnal[4]; };
class Base
{
private:
struct foo *_internal_structure;
public:
Base() { _internal_structure = new struct foo; }
~Base()
{
delete _internal_structure;
std::cout << "Base DTOR\n";
}
};
class Derived: public Base
{
private:
struct bar *_additional_structure;
public:
Derived() { _additional_structure = new struct bar; }
~Derived()
{
delete _additional_structure;
std::cout << "Derived DTOR\n";
}
};
int main(int argc, char *argv[])
{
std::map<int, Base*> my_map;
Base *to_add = new Base();
Derived *derived_to_add = new Derived();
my_map[1] = to_add;
my_map[2] = derived_to_add; // works, derived class, but object gets sliced
/// clear hash map ///
std::map<int, Base*>::const_iterator iter;
for(iter = my_map.begin(); iter != my_map.end(); ++iter)
{
delete (*iter).second;
}
return 0;
}
Result when run:
Base DTOR
Base DTOR
So, thing is, when I insert a Derived class pointer into my map, the underlying object is considered as a Base class; so the destructor called is the one of the Base class, and not the Derived class. Valgrind confirms me that I loose 16 bytes every time.
Also, I can't use Boost's shared_ptr (I saw some mentions of it here), and the embedded architecture I use doesn't support C++ exceptions and RTTI (which in my case, causes some unaligned accesses and other bad stuff)(edit: not related).
Do you know how I can fix this behavior?
Read this, and never forget. Really, you have just broken one of the 10 C++ commandments... :))
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