Re: preprocessor/9689: Number: 9688 update : pasting "<" and "ValidStruct" does not give a valid preprocessing token

Re: preprocessor/9689: Number: 9688 update : pasting "<" and "ValidStruct" does not give a valid preprocessing token

[Zack Weinberg]

The following reply was made to PR preprocessor/9689; it has been noted by GNATS.

From: Zack Weinberg <zack@codesourcery.com>
To: ediaz@veridis.com
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: preprocessor/9689: Number: 9688 update : pasting "<" and
 "ValidStruct" does not give a valid preprocessing token
Date: Thu, 13 Feb 2003 08:56:00 -0800

 ediaz@veridis.com writes:
 
 >
 > #define CM(x)								\
 > template<>								\
 > class C < ##x >							\
 
 This is a shining example of a totally unnecessary use of ##.  Just
 remove it and your code will work.
 
 zw
 

Re: preprocessor/9689: Number: 9688 update : pasting "<" and "ValidStruct" does not give a valid preprocessing token

[neil]

Synopsis: Number: 9688 update : pasting "<" and "ValidStruct" does not give a valid preprocessing token

State-Changed-From-To: open->closed
State-Changed-By: neil
State-Changed-When: Thu Feb 13 10:12:49 2003
State-Changed-Why:
    Not a bug.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9689

preprocessor/9689: Number: 9688 update : pasting "<" and "ValidStruct" does not give a valid preprocessing token

[ediaz]

>Number:         9689
>Category:       preprocessor
>Synopsis:       Number: 9688 update : pasting "<" and "ValidStruct" does not give a valid preprocessing token
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          rejects-legal
>Submitter-Id:   net
>Arrival-Date:   Thu Feb 13 10:06:01 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator:     ediaz@veridis.com
>Release:        g++ (GCC) 3.3 20030212 (prerelease)
>Organization:
>Environment:
SuSE 7.3/Linux
>Description:
c&p of the #9688 descripton :

When I try to compile a file using macros of templates, I get a 'MyFileStruct.h:541:67: pasting "<" and "MyStruct" does not give a valid preprocessing token' message.

It worked perfectly with the 2.95.x serie and with the 3.2.1 version.

I've tryied to do it in two passes, with a --save-temps and a  g++ thefile.ii -c and it worked.  Like if the processed code was not the same as the preprocessor's output.

-----------

I've made a better & cleaner example and attached it :
>How-To-Repeat:
Explanations in test2.cpp
>Fix:
Use the two passes trick.
>Release-Note:
>Audit-Trail:
>Unformatted:
----gnatsweb-attachment----
Content-Type: text/plain; name="test2.cpp"
Content-Disposition: inline; filename="test2.cpp"

/*

This is a better example of the problem (cleaner too)

How to fail :

sh-2.05$ g++ test2.cpp -o test2_fail
test2.cpp:46:11: pasting "<" and "Field" does not give a valid preprocessing token

How to success :

sh-2.05$ g++ test2.cpp --save-temps
test2.cpp:46:11: pasting "<" and "Field" does not give a valid preprocessing token
sh-2.05$ g++ test2.ii -o test2_success           
sh-2.05$

I hope it will helps.

Regards,

Eric Diaz

*/

#include<stdlib.h>
#include<stdio.h>
#include<string.h>

template <class T>
class C
 {
  T hold;
  
  public:
   
    C(T to_hold)
     {
      hold=to_hold;
     }
    
    static void process(T a_value)
     {
      puts("Generic");
      
      return 0;
     }
 };

#define CM(x)														\
template<>														\
class C < ##x >														\
{															\
public:															\
	static void process(x a_value)											\
	{														\
	 puts("Not Generic (" #x ")");											\
	}														\
};

struct Field
{
};

struct Field2
{
};

// The following will fail :

CM( Field )

// The following, being a copy&paste of the .ii output for the CM( Field )  (with Field replaced by Field2) will work.

template<> class C < Field2 > { public: static void process(Field2 a_value) { puts("Not Generic (" "Field2" ")"); } };

int main(int argc,char* argv[])
 {
  Field f1;
  Field2 f2;

  C<Field>::process(f1);
  C<Field2>::process(f2);
 
  return 0;
 }