C #error directive and comments

Question

Given:

#error /*
*/ foo

Microsoft C++ outputs an error message of /* and GCC outputs foo.

Which is correct?

Answer 1

GCC is correct.

Replacement of comments (including line-breaks) happens in translation phase 3, pre-processing in translation phase 4 (ISO/IEC 9899:1999, §5.1.1.2).

Hence, the preprocessing part of the compiler does not "see" the line-breaks anymore.

And, #error is defined like this (§6.10.5):

A preprocessing directive of the form

# error pp-tokens_opt new-line

causes the implementation to produce a diagnostic message that includes the specified sequence of preprocessing tokens.

So, the foo has to be part of the output.

Answer 2

GCC is correct because it should be replaced by a single space / * ... * / in the standard.