预处理器宏扩展为另一个预处理器指令
最初我认为我需要这个，但我最终避免了它.然而，我的好奇心(以及对知识的渴望，哼)让我问:
Initially I thought I needed this, but I eventually avoided it. However, my curiosity (and appetite for knowledge, hum) make me ask:
可以一个预处理器宏，例如
Can a preprocessor macro, for instance in
#include "MyClass.h"
INSTANTIATE_FOO_TEMPLATE_CLASS(MyClass)
扩展到另一个包含，如 in
expand to another include, like in
#include "MyClass.h"
#include "FooTemplate.h"
template class FooTemplate<MyClass>;
?
推荐答案
相信做不到，这是因为预处理器是single pass.所以它不能发出其他预处理器指令.
I believe that cannot be done, this is because the pre-processor is single pass. So it cannot emit other preprocessor directives.
具体来说，来自 C99 标准(6.10.3.4 第 3 段):
Specifically, from the C99 Standard (6.10.3.4 paragraph 3):
3 结果完全宏替换预处理令牌序列不被处理为预处理指令，即使它像一个，...
3 The resulting completely macro-replaced preprocessing token sequence is not processed as a preprocessing directive even if it resembles one, ...
有趣的是，这就是为什么将一元 _Pragma 运算符添加到 c99 中的原因.因为 #pragma 不能由宏发出，但 _Pragma 可以.
Interestingly enough, This is why the unary _Pragma operator was added to c99. Because #pragma could not be emited by macros, but _Pragma can.
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