基于ifdef的继承在C ++中的问题 [英] Problems with ifdef based inheritance in C++

问题描述

我在看一些类的代码，我遇到了这样的代码：

I was looking at the code of some class I was using, and I came across code like this:

#ifdef SOME_OBSCURE_CONDITION
class A {
#elif 
class A : public B {
#endif

这样的代码可能有问题吗？

Can there be any problems with such code?

具体来说，假设x.cpp文件包含y.h和z.h。
z.h和y.h都包括a.h（定义类A），但是另外y.h定义了SOME_OBSCURE_CONDITION。在这种情况下，两个冲突的定义A不会出现在x.cpp中？

Specifically, suppose file x.cpp includes y.h and z.h. z.h and y.h both include a.h (which defines class A), but additionally y.h defines SOME_OBSCURE_CONDITION. In this case, will two conflicting definitions of A not be present in x.cpp?

推荐答案

>同时会违反ODR（一种定义规则），并可能导致

yes, the two variations simultaneously would violate the ODR (One Definition Rule) and may lead to anything ranging from

• 编译错误


• 链接错误


• 未定义的行为（包括但不限于崩溃）

只要您可以确保SOME_OBSCURE_CONDITION定义在全局上是相同的（也是跨部分构建/重新链接），则不会有问题。

As long as you can make sure that the SOME_OBSCURE_CONDITION define is globally identical (also across partial builds/relinks...) there will not be an issue.

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