[Bug c++/26531] New: Use of templates in macro expansion confuses pre-processor

[Bug c++/26531] New: Use of templates in macro expansion confuses pre-processor

[peter dot schuller at infidyne dot com]

Given the following code:

==== BEGIN CODE ====
template <typename A, typename B>
class SomeClass
{
};

#define MYMACRO(BLOCK) \
{                      \
  BLOCK                \
}                      \

int
main(void)
{
  MYMACRO({
    SomeClass<int,int> test;
  });
}
==== END CODE ====

gcc (3.3.5 on Debian sarge, 3.4.4 on FreeBSD 6.0 from base and 4.2.0 on FreeBSD
frmo ports) fails to compile it, complaining that MYMACRO was given too many
arguments. For example, with 4.2.0:

==== BEGIN COMPILER OUTPUT ====
% g++42 -v -save-temps -o macroarg macroarg.cc
Using built-in specs.
Target: i386-portbld-freebsd6.0
Configured with: ./..//gcc-4.2-20060218/configure --disable-nls
--with-system-zlib --with-libiconv-prefix=/usr/loca
ib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++/
--infodir=/usr/local/info/gcc42 --disable-shared --disable-libgcj
--prefix=/usr/local i386-portbld-freebsd6.0
Thread model: posix
gcc version 4.2.0 20060218 (experimental)
 /usr/local/libexec/gcc/i386-portbld-freebsd6.0/4.2.0/cc1plus -E -quiet -v
macroarg.cc -mtune=i386 -fpch-preprocess -o macroarg.ii
ignoring nonexistent directory
"/usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/gcc/i386-portbld-freebsd6.0/4.2.0/../../../../i386-portbld-freebsd6.0/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++/

/usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++//i386-portbld-freebsd6.0
 /usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/include/c++//backward
 /usr/local/include

/usr/local/lib/gcc/i386-portbld-freebsd6.0/4.2.0/gcc/i386-portbld-freebsd6.0/4.2.0/include
 /usr/include
End of search list.
macroarg.cc:16:4: error: macro "MYMACRO" passed 2 arguments, but takes just 1

==== END COMPILER OUTPUT ====

For completeness since it is asked for, following is the pre-processor file
which is incomplete for obvious reasons:

=== BEGIN PRE-PROCESSOR OUTPUT ===
# 1 "macroarg.cc"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "macroarg.cc"
template <typename A, typename B>
class SomeClass
{
};






int
main(void)
{
  MYMACRO;


}
=== END PRE-PROCESSOR OUTPUT ===

It seems to be triggered when the type is parameterized on at least two types.
Removing the MYMACRO({...}) wrapping makes it compile. Putting just about
anything except certain template heavy stuff inside it also compiles.

(The above is obviously a contrived example to trigger the issue; my real usage
is a macro for critical sections with guaranteed mutex cleanup.)


-- 
           Summary: Use of templates in macro expansion confuses pre-
                    processor
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: peter dot schuller at infidyne dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26531

[Bug c++/26531] Use of templates in macro expansion confuses pre-processor

[pinskia at gcc dot gnu dot org]

------- Comment #1 from pinskia at gcc dot gnu dot org  2006-03-02 18:27 -------
This is not a bug.
There are two arguments passed to the macro MYMACRO, "{\n    SomeClass<int" and
"int> test;\n  }".
the only way to force an argument passed to the preprocessor macros is to wrap
them in parentheses.


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26531