23.vector.stdcxx-494.cpp

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#include <cassert>   // for assert()
#include <cstddef>   // for size_t
#include <memory>    // for allocator
#include <vector>    // for vector
 
 
template <class T>
struct EmptyAllocator: std::allocator<T>
{
    template <class U>
    struct rebind { typedef EmptyAllocator<U> other; };
 
    EmptyAllocator () { }
    EmptyAllocator (const EmptyAllocator &rhs)
        : std::allocator<T>(rhs) { }
 
    template <class U>
    EmptyAllocator (const EmptyAllocator<U> &rhs)
        : std::allocator<T>(rhs) { }
 
    void* operator new (std::size_t) { return 0; }
    void operator delete (void*) { }
};
 
 
int main ()
{
    // verify that vector doesn't derive from allocator
    // (otherwise the replacement operator new and delete
    // are in conflict)
 
    typedef std::vector<int, EmptyAllocator<int> > EmptyVector;
 
    delete new EmptyVector;
 
    // verifies empty base optimization
    assert (sizeof (std::vector<int>) == sizeof (EmptyVector));
 
    // assert that the size of vector is exactly 3 pointers
    assert (sizeof (std::vector<int>) == 3 * sizeof (int*));
 
    return 0;
}