Re: uninitialized struct members

[Jim Meyering]

Bruno Haible wrote:
>
>> > -      struct partition part;
>> > +      struct partition part IF_LINT (= { .xmid = 0, .ymid = 0 });
>>
>> Any code using a one-argument macro like that is rejected,
>> due to the comma:
>>
>>     ../lib/diffseq.h:467:64: error: macro "IF_LINT" passed 2 arguments,\
>>     but takes just 1
>>
>> FYI, I tried the same thing before writing the #if-adding patch.
>
> OK, if we both fall into the same trap, it's certainly worth adding a comment.
>
> How about the appended patch? Can I commit this in your name? Or in my name?
> (By default, when combining ideas from several people in a patch, I choose as
> --author the person who has contributed the majority of ideas or code.)

I have no objection to the practice, in general.
The only trouble is when a modification induces incorrectness
or a stylistic disagreement.

>> Please do not push that, at least not with my name on it...
>
> Oops, glad that I forgot to push it...
...
> -/* Use this to suppress gcc's `...may be used before initialized' warnings. 
> */
> +/* Use this to suppress gcc's `...may be used before initialized' warnings.
> +   Beware: The Code argument must not contain commas.  */
>  #ifndef IF_LINT
>  # ifdef lint
>  #  define IF_LINT(Code) Code
> @@ -465,6 +466,8 @@
>    else
>      {
>        struct partition part;
> +      IF_LINT (part.xmid = 0;)
> +      IF_LINT (part.ymid = 0;)

I avoid using IF_LINT (stmt;) because the result can no longer
be handled properly by automatic code formatters;

I would prefer this:

>From 672ecc5c795cd74d36a3e4fad3afe5070b3196d0 Mon Sep 17 00:00:00 2001
From: Jim Meyering <address@hidden>
Date: Sun, 22 Nov 2009 09:01:07 +0100
Subject: [PATCH] diffseq: avoid spurious gcc warnings

* lib/diffseq.h (IF_LINT2): Define.
(compareseq): Use it to initialize two members of "part".
This avoids two used-uninitialized warnings.
---
 ChangeLog     |    7 +++++++
 lib/diffseq.h |   11 ++++++++++-
 2 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 04b2a6b..9f8d4ef 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2009-11-22  Jim Meyering  <address@hidden>
+
+       diffseq: avoid spurious gcc warnings
+       * lib/diffseq.h (IF_LINT2): Define.
+       (compareseq): Use it to initialize two members of "part".
+       This avoids two used-uninitialized warnings.
+
 2009-11-21  Jim Meyering  <address@hidden>

        c-stack: avoid "ignoring return value of `write'" warning
diff --git a/lib/diffseq.h b/lib/diffseq.h
index 0c1723f..9c7baa6 100644
--- a/lib/diffseq.h
+++ b/lib/diffseq.h
@@ -77,6 +77,15 @@
 # endif
 #endif

+/* As above, but when Code must contain one comma. */
+#ifndef IF_LINT2
+# ifdef lint
+#  define IF_LINT2(Code1, Code2) Code1, Code2
+# else
+#  define IF_LINT2(Code1, Code2) /* empty */
+# endif
+#endif
+
 /*
  * Context of comparison operation.
  */
@@ -464,7 +473,7 @@ compareseq (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET 
ylim,
       }
   else
     {
-      struct partition part;
+      struct partition part IF_LINT2 (= { .xmid = 0, .ymid = 0 });

       /* Find a point of correspondence in the middle of the vectors.  */
       diag (xoff, xlim, yoff, ylim, find_minimal, &part, ctxt);
--
1.6.5.2