C ++切片导致泄漏/未定义的行为/崩溃 [英] C++ slicing causing leak / undefined behavior / crash

问题描述

有什么C ++对象切片效应的例子可以导致未定义的行为，内存泄漏或崩溃在其他正确的代码集？例如，当类 A 和 B （继承自 A ）是正确和健全的，但调用 void f（A a）可以引起讨厌的事情。

Is there any example of the C++ object slicing effect which can cause undefined behavior, memory leak or crash in an otherwise correct set of code? For example when class A and B (inherited from A) are correct and sound, but calling a void f(A a) demonstrably causes nasty things.

需要形成一个测试问题。目标是使用示例代码片段知道参与者是否知道切片现象，其正确性不能是意见问题。

It is needed for forming a test question. The goal is to know if the participant is aware of the slicing phenomenon or not, using an example code snippet whose correctness must not be a matter of opinion.

推荐答案

如果 A 确实是正确和健全，则切片（复制基础子对象）是明确定义的，你提到的问题。如果你期望副本的行为像 B 。

If A is indeed "correct and sound", then slicing (copying the base sub-object) is well-defined and will not cause any of the problems you mention. The only problem it will cause is unexpected behaviour, if you expect the copy to behave like B.

如果 A 无法正确复制，则切片将导致复制该类型对象时出现的任何问题。例如，如果它有一个析构函数删除一个由对象持有的指针，并且复制创建一个新的指针指向同一个事物，那么当两个析构函数删除同一个指针时，你会得到未定义的行为。这不是切片本身的问题，而是切片对象的无效复制语义。

If A is not correctly copyable, then slicing will cause whatever problems arise from copying objects of that type. For example, if it has a destructor which deletes a pointer held by object, and copying creates a new pointer to the same thing, then you will get undefined behaviour when both destructors delete the same pointer. This isn't a problem with slicing as such, but with invalid copy semantics of the sliced object.

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