[Bug preprocessor/37373] New: Variadic macros fail when generated by other macros.

["jkrahn at nc dot rr dot com" <gcc-bugzilla at gcc dot gnu dot org>]

The preprocessor does not parse variadic macros correctly when they are used in
source code generated by other macros. I think that directives within macros
are non-standard, but some standard library functions are implemented as macros
when using FORTIFY_SOURCE, which can cause problems in code that is otherwise
valid.

For example, I am compiling code that uses macros to add extra code for
handling formatted messages in some contexts, similar to the following example:

#define printf(...) printf(stdout,__VA_ARGS__)

#define PRINT_BEGIN(fmt) printf(fmt,
#define PRINT_END        )

PRINT_BEGIN("%d")
  100
PRINT_END;


The result is:
tmp.c:9:1: error: unterminated argument list invoking macro "printf"

Obviously, the code can be modified to use macros without splitting the
printf() call into separate macro evaluations. However, given that the code is
valid, it would be nice if system headers could use variadic macros without
breaking valid code.

For now, this may only happens when invoking non-standard features like
FORTIFY_SOURCE, and not with standard system headers. If so, may really be a
feature request, depending on whether those features are intended to be free of
side effects.


-- 
           Summary: Variadic macros fail when generated by other macros.
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: trivial
          Priority: P3
         Component: preprocessor
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jkrahn at nc dot rr dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37373