Item 36. Memory Management桺art 2
Difficulty: 6
Are you thinking about doing your own class-specific memory management, or even replacing C++'s global new and delete? First, try this problem on for size.
The following code shows classes that perform their own memory management. Point out as many memory-related errors as possible, and answer the additional questions.
Consider the following code:
class B
{
public:
virtual ~B();
void operator delete ( void*, size_t ) throw();
void operator delete[]( void*, size_t ) throw();
void f( void*, size_t ) throw();
};
class D : public B
{
public:
void operator delete ( void* ) throw();
void operator delete[]( void* ) throw();
};
Why do B's operators delete have a second parameter, whereas D's do not? Do you see any way to improve the function declarations? Continuing with the same piece of code: Which operator delete() is called for each of the following delete expressions? Why, and with what parameters?
D* pd1 = new D;
delete pd1;
B* pb1 = new D;
delete pb1;
D* pd2 = new D[10];
delete[] pd2;
B* pb2 = new D[10];
delete[] pb2;
Are the following two assignments legal?
typedef void (B::*PMF)(void*, size_t);
PMF p1 = &B::f;
PMF p2 = &B::operator delete;
Are there any memory-related errors or issues in the following code?
class X
{
public:
void* operator new( size_t s, int )
throw( bad_alloc )
{
return ::operator new( s );
}
};
class SharedMemory
{
public:
static void* Allocate( size_t s )
{
return OsSpecificSharedMemAllocation( s );
}
static void Deallocate( void* p, int i = 0 )
{
OsSpecificSharedMemDeallocation( p, i );
}
};
class Y
{
public:
void* operator new( size_t s,
SharedMemory& m ) throw( bad_alloc )
{
return m.Allocate( s );
}
void operator delete( void* p,
SharedMemory& m,
int i ) throw()
{
m.Deallocate( p, i );
}
};
void operator delete( void* p ) throw()
{
SharedMemory::Deallocate( p );
}
void operator delete( void* p,
std::nothrow_t& ) throw()
{
SharedMemory::Deallocate( p );
}
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