“Multiple include guards may be useful for” what, exactly?
问题 I've been playing around with the -H option of gcc, which prints out information about direct and indirect includes in C and C++ compilation (relevant section of the gcc manual). As part of the output there's a section "Multiple include guards may be useful for:", which lists a number of project and system headers. What does this mean, how is this list determined, and why is it saying "Multiple" include guards may be useful? (I'm familiar with the general concept of include guards, and why