带有宏值串联的C ++`ifdef` [英] C++ `ifdef` with concatenation of macros values

问题描述

我是否可以实现类似于以下代码的内容：

Can I achieve something similar to following code:

#define MODULE base
#if defined (MODULE ## _dll)      <-- this should do `#ifdef base_dll`
    ...
#else
    ...
#endif

第二行显然是错误的。我可以以某种方式执行此操作吗？

second line is obviously wrong. Can I do this somehow?

谢谢

推荐答案

我不这样做认为可以像这样检查令牌粘贴的宏的定义（至少我不知道这种方式），但是您可以这样做：

I don't think it is possible to check the definition of token-pasted macro like that (at least I don't know the way) but you can do this:

#define JOIN_INTERNAL(a,b) a ## b
#define JOIN(a,b) JOIN_INTERNAL(a,b)

// switch 1/0
#define base_dll 1

#define MODULE base

#if JOIN(MODULE,_dll)
// the base_dll is 1
#else
// the base_dll is 0 or not defined (in MSVC at least)
#endif

也许，如果您描述了您实际想要实现的目标，那么可能还有另一种方法。

Perhaps if you describe what do you actually want to achieve there might be another way to do that.

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