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

Question

I have a question about preprocessor 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?

Answer 1

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

For example,

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