How does the C preprocessor handle circular dependencies?

Question

I want to know how the C preprocessor handles circular dependencies (of #defines). This is my program:

#define ONE TWO 
#define TWO THREE
#defi         


        

Answer 1

Your question is answered by publication ISO/IEC 9899:TC2 section 6.10.3.4 "Rescanning and further replacement", paragraph 2, which I quote here for your convenience; in the future, please consider reading the specificaftion when you have a question about the specification.

If the name of the macro being replaced is found during this scan of the replacement list (not including the rest of the source file’s preprocessing tokens), it is not replaced. Furthermore, if any nested replacements encounter the name of the macro being replaced, it is not replaced. These nonreplaced macro name preprocessing tokens are no longer available for further replacement even if they are later (re)examined in contexts in which that macro name preprocessing token would otherwise have been replaced.