c preprocessor - Can #if pre-processor directives be nested in C++?

Question

posted Oct 17, 2021 in Technique[技术] by 深蓝 (71.8m points)

I have a question about Pre-processor directives in c++:

For example:

#ifndef QUESTION

//some code here

#ifndef QUESTION

//some code here

#endif

#endif

Can we use it in this way, and can the C++ compiler match the ifndef and endif in the right way?

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1 Reply

深蓝 · Answer 1 · 2021-10-17T02:47:43+0000

Yes, we can. The #endif statement matches to the previous #if #ifdef or #ifndef etc for which there hasn't been a corresponding #endif.

e.g.

#if  ----------|
#if  -----|    |
#endif ---|    |
#endif --------|