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 我怀疑有几个因素导致这个未定义，但我们只需要一个： 
 
 
 
 [C++11: 3.8/1]: [..] 类型T对象的生命周期结束时 ： 
 
 
 
  
 如果T是具有非平凡析构函数（12.4）的类类型，则析构函数调用将启动，或者 
 
  
 对象占用的存储器被重用或释放。 
 
 
 
 
 所有后续使用都是在使用寿命结束后使用，这是坏事和错误。 
 
 关键是每个缓冲区都在重用。 
 
 所以，虽然我希望这在实践中起作用，至少对于琐碎的类型（以及某些类），它是未定义的。 
 
 
 以下可能能够为您节省： 
 
 
 
 [C++11: 3.8/7]:如果在对象的生命周期结束之后，在重用或释放对象占用的存储之前，在原始对象占用的存储位置创建一个新对象，指向原始对象的指针，引用原始对象的引用，或原始对象的名称将自动引用新对象，并且一旦新对象的生命周期开始，就可以用来操纵新对象对象[...] 
 
 
 ...除了你没有创建一个新对象。 
 
 在这里可能或者可能不值得注意，令人惊讶的是，随后的隐式析构函数调用都是明确定义的： 
 
 
 
 [C++11: 3.8/8]:如果程序以静态（3.7.1），线程（3.7.2）或自动（3.7.3）存储持续时间结束T类型对象的生命周期，如果T有一个非平凡的析构函数，程序必须确保在隐式析构函数调用发生时，原始类型的对象占用相同的存储位置; 否则程序的行为是不确定的。 
 

I suspect there are a few factors rendering this undefined, but we only need one:
 
 
 
[C++11: 3.8/1]: [..] The lifetime of an object of type T ends when:
 
 
 
  
if T is a class type with a non-trivial destructor (12.4), the destructor call starts, or
 
  
the storage which the object occupies is reused or released.
 
 
 
 
All subsequent use is use after end-of-life, which is bad and wrong.
 
The key is that each buffer is being reused.
 
So, although I would expect this to work in practice at least for trivial types (and for some classes), it's undefined.
 
 
The following may have been able to save you:
 
 
 
[C++11: 3.8/7]: If, after the lifetime of an object has ended and before the storage which the object occupied is reused or released, a new object is created at the storage location which the original object occupied, a pointer that pointed to the original object, a reference that referred to the original object, or the name of the original object will automatically refer to the new object and, once the lifetime of the new object has started, can be used to manipulate the new object [..]
 
 
…except that you are not creating a new object.
 
It may or may not be worth noting here that, surprisingly, the ensuing implicit destructor calls are both well-defined:
 
 
 
[C++11: 3.8/8]: If a program ends the lifetime of an object of type T with static (3.7.1), thread (3.7.2), or automatic (3.7.3) storage duration and if T has a non-trivial destructor, the program must ensure that an object of the original type occupies that same storage location when the implicit destructor call takes place; otherwise the behavior of the program is undefined.