handle constructor failure

[dsaharan]

when the constructor throws exception how is the memory allocated to the object is reverted back.for example
class x
{
public:
x()
{}
~x()
{}
};
int main()
{
try{
x *a=new x();
}
catch(...)
{}
}
Now if the constructor throws exception ,the memory allocated on heap how would it be reverted as the destructor of partially initialised object can not be called ??