是不作为的行为吗？

Question

1.3.24                                                          [defns.undefined]
undefined behavior
behavior for which this International Standard imposes no requirements
[ Note: Undefined behavior may be expected when this International Standard 
omits any explicit definition of behavior or when a program uses an erroneous 
construct or erroneous data. Permissible undefined behavior ranges from ignoring 
the situation completely with unpredictable results, to behaving during 
translation or program execution in a documented manner characteristic of the 
environment (with or without the issuance of a diagnostic message), to 
terminating a translation or execution (with the issuance of a diagnostic 
message). Many erroneous program constructs do not engender undefined behavior; 
they are required to be diagnosed.
— end note ]

Answer 1

但是，标准怎么能说某件事是未定义的行为而不明确地这样说呢？

因为这就是未定义的意思。发生了什么还没有定义。标准定义了对有效程序的期望，它并不试图列出每一个可能的无效程序，并说“这是未定义的，也是未定义的，也是未定义的”。

该标准没有规定如果你在程序运行时点燃了你的计算机会发生什么。这并不意味着它的定义很好。显然没有定义。