preprocessor/7976: macro definition

preprocessor/7976: macro definition

[stoppel]

>Number:         7976
>Category:       preprocessor
>Synopsis:       macro definition
>Confidential:   no
>Severity:       critical
>Priority:       low
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Sep 19 04:46:02 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     National Bank of Poland
>Release:        gcc version 3.1
>Organization:
>Environment:
HPUX 10.20 hw:K460, HPUX 11.00 hw:J5000, GNU/Linux Debian 2.2.17
>Description:
Execution of some mocro definition yield unexpected results:
"cpp" reports:
> 
> cpp-define.c:22:13 warning: pasting ")" and "l"
> does not give a valid preprocessing token
> 
>How-To-Repeat:
"cpp-define.c" is the attached file
gcc -E cpp cpp-define.c
cpp cpp-define.c
>Fix:
I do not know.
>Release-Note:
>Audit-Trail:
>Unformatted:
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Content-Type: application/octet-stream; name="cpp-define.c"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="cpp-define.c"

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Re: preprocessor/7976: macro definition

[Andreas Schwab]

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The following reply was made to PR preprocessor/7976; it has been noted by GNATS.

From: Andreas Schwab <schwab@suse.de>
To: neil@gcc.gnu.org
Cc: gcc-bugs@gcc.gnu.org, gcc-prs@gcc.gnu.org, nobody@gcc.gnu.org,
	stoppel@immt.pwr.wroc.pl, gcc-gnats@gcc.gnu.org
Subject: Re: preprocessor/7976: macro definition
Date: Thu, 19 Sep 2002 15:45:21 +0200

 neil@gcc.gnu.org writes:
 
 |> Synopsis: macro definition
 |> 
 |> State-Changed-From-To: closed->open
 |> State-Changed-By: neil
 |> State-Changed-When: Thu Sep 19 06:13:38 2002
 |> State-Changed-Why:
 |>     Sorry, ignore previous message.  I'll look at this later.
 
 IMHO your previous analysis was right.
 
 UINT32_C(123) ->
 __CONCAT__(__CONCAT_U__(123),l) ->
 __CONCAT_U__(123) ## l
 
 and )l is not a token.  This needs to be written like this:
 
 #define __CONCAT2__(_A,_B) _A ## _B
 #define __CONCAT__(_A,_B) __CONCAT2__(_A,_B)
 #define __CONCAT_U__(_A) _A ## u
 #define UINT32_C(__c) __CONCAT__(__CONCAT_U__(__c),l)
 
 Andreas.
 
 -- 
 Andreas Schwab, SuSE Labs, schwab@suse.de
 SuSE Linux AG, Deutschherrnstr. 15-19, D-90429 Nürnberg
 Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
 "And now for something completely different."

Re: preprocessor/7976: macro definition

[neil]

Synopsis: macro definition

State-Changed-From-To: open->closed
State-Changed-By: neil
State-Changed-When: Thu Sep 19 06:19:59 2002
State-Changed-Why:
    Not a bug.
    
    #define __CONCAT__(_A,_B) _A ## _B
    #define __CONCAT_U__(_A) _A ## u
    #define UINT32_C(__c) __CONCAT__(__CONCAT_U__(__c),l)
    UINT32_C(123)
    
    The bug in your macro occurs during the expansion of UINT32_C.  Since, in the definition of __CONCAT__, the
    first argument is operated on by ##, it is not expanded
    before replacement.  Therefore, the first stage of
    expansion is
    UINT32_C(123)
    __CONCAT__(__CONCAT_U__(123),l)
    __CONCAT_U__(123)##l
    
    which is not what you want, and gives rise to the (correct)
    warning you see.  You want the argument to be
    expanded, and so you need an extra level of indirection:
    
    #define __CONCAT_INDIRECT(_A,_B) __CONCAT(_A,_B)
    #define __CONCAT__(_A,_B) _A ## _B
    #define __CONCAT_U__(_A) _A ## u
    #define UINT32_C(__c) _CONCAT_INDIRECT__(__CONCAT_U__(__c),l)
    UINT32_C(123)
    
    If HPUX AnsiC gives the answer you wanted, then it's simply
    not ANSI 8-)
    
    Neil.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7976

Re: preprocessor/7976: macro definition

[neil]

Synopsis: macro definition

State-Changed-From-To: closed->open
State-Changed-By: neil
State-Changed-When: Thu Sep 19 06:13:38 2002
State-Changed-Why:
    Sorry, ignore previous message.  I'll look at this later.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7976

Re: preprocessor/7976: macro definition

[neil]

Synopsis: macro definition

State-Changed-From-To: open->closed
State-Changed-By: neil
State-Changed-When: Thu Sep 19 06:11:22 2002
State-Changed-Why:
    Not a bug.  You have a ## in your macro definition that
    is being used to create a token from ")" and "l" by
    concatenation.  No such token exists.
    
    You can probably remove the ## in question.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7976