new在类里面重载后声明的问题

Class A
{
public:
       ...
       void* operator new(size_t n) {return ExAllocatePool(NonPagedPool,n);}
       void operator delete(void* p) {ExFreePool(p);}
}

另一个cpp里面调用：
void B()
{
     A a = new A;
}
 出现错误:error LNK2019: unresolved external symbol "void * __cdecl operator new(unsigned int)" (??2@YAPAXI@Z) referenced in function "void __stdcall B(void)" (?B@@YGXXZ)

请教各位大虾