Re: "unused parameter" warnings

[Bruno Haible]

Jim Meyering wrote:
> However, it would be good to accept patches (at least for gnulib's .h
> files) that mark each unused parameter with __attribute__ ((__unused__)).
> Then, a project that requires use of -Wunused-parameter can use gnulib's
> headers without having to relax their standards.

I agree regarding gnulib's public .h files. I'll handle unistr.h.

> although I admit to disliking the seemingly necessary duplication of
> the snippet to define __attribute__.

One could define __attribute__, or a special-purpose macro, in an extra
module. But then keeping track of the module dependency is some work.
It's easier to define it in generated config.h always.

I propose this. A special-purpose macro called _UNUSED_PARAMETER_ is as
understandable as is __attribute__ ((__unused__)), and may accomodate other
compilers (whereas #defining __attribute__ is gcc specific).

gcc 2.7.2.3 already supported __attribute__ ((__unused__)), as far as I can
see.


2008-10-18  Bruno Haible  <address@hidden>

        Avoid -Wunused-parameter warnings in public gnulib header files.
        * m4/gnulib-common.m4 (gl_COMMON_BODY): Define _UNUSED_PARAMETER_ as a
        macro.
        * lib/unistr.h (u32_mbtouc_unsafe, u32_mbtouc): Use it.

--- m4/gnulib-common.m4.orig    2008-10-18 20:28:22.000000000 +0200
+++ m4/gnulib-common.m4 2008-10-18 19:59:26.000000000 +0200
@@ -1,4 +1,4 @@
-# gnulib-common.m4 serial 5
+# gnulib-common.m4 serial 6
 dnl Copyright (C) 2007-2008 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -21,6 +21,16 @@
 #if defined __APPLE__ && defined __MACH__ && __APPLE_CC__ >= 5465 && !defined 
__cplusplus && __STDC_VERSION__ >= 199901L && !defined __GNUC_STDC_INLINE__
 # define __GNUC_STDC_INLINE__ 1
 #endif])
+  AH_VERBATIM([unused_parameter],
+[/* Define as a marker that can be attached to function parameter declarations
+   for parameters that are not used.  This helps to reduce warnings, such as
+   from GCC -Wunused-parameter.  */
+#if __GNUC__ >= 3 || (__GNUC__ == 2 && __GNUC_MINOR__ >= 7)
+# define _UNUSED_PARAMETER_ __attribute__ ((__unused__))
+#else
+# define _UNUSED_PARAMETER_
+#endif
+])
 ])
 
 # gl_MODULE_INDICATOR([modulename])
--- lib/unistr.h.orig   2008-10-18 20:28:22.000000000 +0200
+++ lib/unistr.h        2008-10-18 20:27:39.000000000 +0200
@@ -1,5 +1,5 @@
 /* Elementary Unicode string functions.
-   Copyright (C) 2001-2002, 2005-2007 Free Software Foundation, Inc.
+   Copyright (C) 2001-2002, 2005-2008 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify it
    under the terms of the GNU Lesser General Public License as published
@@ -183,7 +183,7 @@
        u32_mbtouc_unsafe (ucs4_t *puc, const uint32_t *s, size_t n);
 # else
 static inline int
-u32_mbtouc_unsafe (ucs4_t *puc, const uint32_t *s, size_t n)
+u32_mbtouc_unsafe (ucs4_t *puc, const uint32_t *s, size_t n _UNUSED_PARAMETER_)
 {
   uint32_t c = *s;
 
@@ -253,7 +253,7 @@
        u32_mbtouc (ucs4_t *puc, const uint32_t *s, size_t n);
 # else
 static inline int
-u32_mbtouc (ucs4_t *puc, const uint32_t *s, size_t n)
+u32_mbtouc (ucs4_t *puc, const uint32_t *s, size_t n _UNUSED_PARAMETER_)
 {
   uint32_t c = *s;