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* [Bug preprocessor/35010] New: preprocessor loses leading whitespace
@ 2008-01-29 9:33 sabre at nondot dot org
2008-05-15 2:55 ` [Bug preprocessor/35010] " neil at gcc dot gnu dot org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: sabre at nondot dot org @ 2008-01-29 9:33 UTC (permalink / raw)
To: gcc-bugs
This testcase:
#define debug(format, ...) format, ## __VA_ARGS__)
debug(X);
debug(Y, 1, 2);
debug(Y, 1, 2 );
debug(Z, );
debug(W,);
Should preprocess to:
X);
Y, 1, 2);
Y, 1, 2);
Z, );
W, );
not:
X);
Y, 1, 2);
Y, 1, 2);
Z,);
W,);
Z/W should have spaces.
--
Summary: preprocessor loses leading whitespace
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: sabre at nondot dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35010
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug preprocessor/35010] preprocessor loses leading whitespace
2008-01-29 9:33 [Bug preprocessor/35010] New: preprocessor loses leading whitespace sabre at nondot dot org
@ 2008-05-15 2:55 ` neil at gcc dot gnu dot org
2008-05-15 2:57 ` neil at gcc dot gnu dot org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: neil at gcc dot gnu dot org @ 2008-05-15 2:55 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from neil at gcc dot gnu dot org 2008-05-15 02:54 -------
Chris - unless I'm missing something I disagree. The
, ## __VA_ARGS__
token sequence is being eaten in its entirety by the empty argument. Then
between "format" and the ')' on the #define line, which is the ')' that appears
on the output, there is no whitespace. It seems GCC's output is correct to me.
--
neil at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |neil at gcc dot gnu dot org
Status|UNCONFIRMED |WAITING
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35010
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug preprocessor/35010] preprocessor loses leading whitespace
2008-01-29 9:33 [Bug preprocessor/35010] New: preprocessor loses leading whitespace sabre at nondot dot org
2008-05-15 2:55 ` [Bug preprocessor/35010] " neil at gcc dot gnu dot org
@ 2008-05-15 2:57 ` neil at gcc dot gnu dot org
2009-04-08 17:46 ` b07584 at freescale dot com
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: neil at gcc dot gnu dot org @ 2008-05-15 2:57 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from neil at gcc dot gnu dot org 2008-05-15 02:56 -------
Never mind, I see your point. The comma isn't being eaten, right.
--
neil at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2008-05-15 02:56:17
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35010
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug preprocessor/35010] preprocessor loses leading whitespace
2008-01-29 9:33 [Bug preprocessor/35010] New: preprocessor loses leading whitespace sabre at nondot dot org
2008-05-15 2:55 ` [Bug preprocessor/35010] " neil at gcc dot gnu dot org
2008-05-15 2:57 ` neil at gcc dot gnu dot org
@ 2009-04-08 17:46 ` b07584 at freescale dot com
2009-04-27 1:31 ` sabre at nondot dot org
2009-04-27 1:32 ` sabre at nondot dot org
4 siblings, 0 replies; 6+ messages in thread
From: b07584 at freescale dot com @ 2009-04-08 17:46 UTC (permalink / raw)
To: gcc-bugs
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------- Comment #3 from b07584 at freescale dot com 2009-04-08 17:46 -------
(In reply to comment #0)
> This testcase:
>
> #define debug(format, ...) format, ## __VA_ARGS__)
> debug(X);
> debug(Y, 1, 2);
> debug(Y, 1, 2 );
> debug(Z, );
> debug(W,);
>
> Should preprocess to:
>
> X);
> Y, 1, 2);
> Y, 1, 2);
> Z, );
> W, );
>
> not:
>
> X);
> Y, 1, 2);
> Y, 1, 2);
> Z,);
> W,);
>
>
> Z/W should have spaces.
>
Chris, I want to make sure I understand what you are saying. With:
#define debug(format, ...) format, ## __VA_ARGS__)
For the the invocation:
debug(X);
- the argument is omitted and hence the comma preceeding ## in the body is
removed in accordance with GNU CPP's extended semantics, yielding:
X);
In contrast, for the invocations:
debug(Z, );
debug(W,);
when you say, the output ought to be:
Z, );
W, );
- is it because a space preceeds the ## in the macro definition (i.e. body)?
So, if the definition were to be:
#define debug(format, ...) format,## __VA_ARGS__)
instead, then:
debug(Z, );
debug(W,);
preprocessing to:
Z,);
W,);
would be OK? This reasoning about the appearance (or non-appearance) of space
is similar to Neil's explanation in the Cpplib Internals manual (for GCC
version 4.4.0) in the section Token Spacing:
#define add(x, y, z) x + y +z
sum = add (1,2, 3)
preprocesses to:
sum = 1 + 2 +3
However in the case at hand, per ISO/IEC 9899:TC2 Committee Draft May 6,
2005 WG14/N1124, 6.10.3.3 "The ## operator", constraint 2: "... however, if an
argument consists of no preprocessing tokens, the parameter is replaced by a
placemarker preprocessing token instead." Further, in constraint 3:
"... concatenation of a placemarker with a non-placemarker preprocessing token
results in the non-placemarker preprocessing token."
By that, the expansion sequence for (say):
debug(Z, );
(with the first definition - i.e. the one with a space before the ##) would
be:
debug(Z, );
->
format, ## __VA_ARGS__)
(CPP_COMMA gets the PASTE_LEFT flag set, and <placemarker> is only conceptually
depicted per constraint 2)
->
CPP_NAME CPP_COMMA[PASTE_LEFT] <placemarker> CPP_CLOSE_PAREN CPP_SEMICOLON
(per constraint 3, CPP_COMMA and <placemarker> concatenate to CPP_COMMA)
->
CPP_NAME CPP_COMMA CPP_CLOSE_PAREN CPP_SEMICOLON
So, the space before the ## does not make it to the expansion because this is
the paste operation in operation - as it proceeds normally.
Or perhaps, I am missing something? Kindly explain. Thanks.
--
b07584 at freescale dot com changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |b07584 at freescale dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35010
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug preprocessor/35010] preprocessor loses leading whitespace
2008-01-29 9:33 [Bug preprocessor/35010] New: preprocessor loses leading whitespace sabre at nondot dot org
` (2 preceding siblings ...)
2009-04-08 17:46 ` b07584 at freescale dot com
@ 2009-04-27 1:31 ` sabre at nondot dot org
2009-04-27 1:32 ` sabre at nondot dot org
4 siblings, 0 replies; 6+ messages in thread
From: sabre at nondot dot org @ 2009-04-27 1:31 UTC (permalink / raw)
To: gcc-bugs
------- Comment #4 from sabre at nondot dot org 2009-04-27 01:31 -------
If the definition is:
#define debug(format, ...) format,## __VA_ARGS__)
Then we should still get:
Z, );
W, );
If the definition is:
#define debug(format,...) format,##__VA_ARGS__)
Then we should get:
Z,);
W,);
(and gcc currently gets this right)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35010
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug preprocessor/35010] preprocessor loses leading whitespace
2008-01-29 9:33 [Bug preprocessor/35010] New: preprocessor loses leading whitespace sabre at nondot dot org
` (3 preceding siblings ...)
2009-04-27 1:31 ` sabre at nondot dot org
@ 2009-04-27 1:32 ` sabre at nondot dot org
4 siblings, 0 replies; 6+ messages in thread
From: sabre at nondot dot org @ 2009-04-27 1:32 UTC (permalink / raw)
To: gcc-bugs
------- Comment #5 from sabre at nondot dot org 2009-04-27 01:31 -------
Sorry I can't give a more detailed analysis of what is going on, I have no idea
how the placemarker system works in gcc.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35010
^ permalink raw reply [flat|nested] 6+ messages in thread
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2008-01-29 9:33 [Bug preprocessor/35010] New: preprocessor loses leading whitespace sabre at nondot dot org
2008-05-15 2:55 ` [Bug preprocessor/35010] " neil at gcc dot gnu dot org
2008-05-15 2:57 ` neil at gcc dot gnu dot org
2009-04-08 17:46 ` b07584 at freescale dot com
2009-04-27 1:31 ` sabre at nondot dot org
2009-04-27 1:32 ` sabre at nondot dot org
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