条款10如果写了operator new就要同时写operator delete（Clause 10 if you write operator new, write operator delete at the same time）.doc

条款10如果写了operator new就要同时写operator delete（Clause 10 if you write operator new, write operator delete at the same time） Clause 10: if you write operator new, write operator delete at the same time Lets look back at the basic question: why is it necessary to write your own operator, new, and operator delete? The answer is usually: for efficiency. The default operator, new, and operator delete have very good versatility, and its flexibility makes it possible to further improve its performance in certain situations. This is especially true in applications where large numbers of small objects need to be dynamically distributed. For example, there is a class that represents an aircraft: class airplane contains only one pointer, and it points to the actual description of the aircraft object (this technique is explained in Clause 34): Class airplanerep {...}; / / a plane object / / Class airplane { Public: ... Private: Airplanerep *rep; / / pointer to the actual description }; A airplane object is not large; it contains only one pointer (as explained in Clauses 14 and M24, and if the airplane class declares a virtual function, it implicitly contains second pointers). But when you call operator new to assign a airplane object, you can get more memory than you need to store this pointer (or a pair of pointers). The reason for this strange looking behavior is that operator, new, and operator delete need to communicate information to each other. Because the default version of operator new is a generic memory allocator, it must be able to allocate blocks of memory of any size. Similarly, operator delete also frees memory blocks of any size. Operator delete wants to know how much memory it is going to release, so you have to know how much memory is allocated at the beginning of operator new. There is a commonly used method allows operator new to tell operator that delete had allocated memory size is much, it is in the memory in advance to return with some additional information us