在编译/链接期间，是否会删除#ifdef和#endif中无法访问的代码？

Question

Does unreachable code within #ifdef and #endif get removed during compile/link time or kept in the executable even though it can not be reached?

#ifdef DEBUG
// some debug operations
#endif

Is the debug operation code still kept after compilation without DEBUG flag, and if it is will it affect the performance of release build?

EDIT:

If there were some modules used only in the debug operation, and if it is linked into the program, will this affect the performance?

Answer 1

The preprocessor will completely remove such code - the compiler doesn't even get to see it.

You can eg use g++ -E to have a look at what the preprocessor does, and what the compiler gets to see.

Answer 2

它由预处理器删除（使用外部预处理器时，通常会替换为空行）。