Working of the C Preprocessor

Question

How does the following piece of code work, in other words what is the algorithm of the C preprocessor? Does this work on all compilers?

#include 

        

Answer 1

It's at §6.10.3 (Macro Replacement):

6.10.3.4 Rescanning and further replacement

1) After all parameters in the replacement list have been substituted and # and ## processing has taken place, all placemarker preprocessing tokens are removed. Then, the resulting preprocessing token sequence is rescanned, along with all subsequent preprocessing tokens of the source file, for more macro names to replace.

Further paragraphs state some complementary rules and exceptions, but this is basically it.

Though it may violate some definitions of "single pass", it's very useful. Like the recursive preprocessing of included files (§5.1.1.2p4).