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- Log -----------------------------------------------------------------
commit 801f3ad85b22a5da5114bfb47d74c94033806f24
Author: David Malcolm <dmalc...@redhat.com>
Date: Wed Jan 15 14:08:24 2025 -0500
gcc-15/porting_to: c23-fn-decls-without-parameters
diff --git a/htdocs/gcc-15/porting_to.html b/htdocs/gcc-15/porting_to.html
index 39598b93..c446e309 100644
--- a/htdocs/gcc-15/porting_to.html
+++ b/htdocs/gcc-15/porting_to.html
@@ -41,7 +41,69 @@ If your code relies on older versions of the C standard, you
will need to
either add <a
href="https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html#index-std-1";>-std=</a>
to your build flags, or port your code to C23.
-<!-- C23 brings the following changes: -->
+C23 brings the following changes:
+
+<h4 id="c23-fn-decls-without-parameters">Function declarations without
parameters</h4>
+<p>
+ The meaning of function declarations of the form
+ <code>rettype identifier ();</code>
+ such as
+ <code>char *strstr ();</code>
+ changed in C23.
+</p>
+<p>
+ In C17 and earlier, such function declarators specified no information
+ about the number or types of the parameters of the function (C17 6.7.6.3),
+ requiring users to know the correct number of arguments, with each passed
+ argument going through default argument promotion.
+</p>
+<p>
+ In C23 such declarations mean <code>(void)</code> i.e. a function taking
+ no arguments, which can lead to build failures on code that relied on
+ the earlier meaning, such as in
+ <a href="https://godbolt.org/z/11hzWYEeK";>this example</a>:
+</p>
+<pre><code>
+#include <signal.h>
+
+void test()
+{
+ void (*handler)();
+ handler = signal(SIGQUIT, SIG_IGN);
+}
+
+<source>: In function 'test':
+<source>:6:11: error: assignment to 'void (*)(void)' from incompatible
pointer type '__sighandler_t' {aka 'void (*)(int)'}
[-Wincompatible-pointer-types]
+ 6 | handler = signal(SIGQUIT, SIG_IGN);
+ | ^
+In file included from <source>:1:
+/usr/include/signal.h:72:16: note: '__sighandler_t' declared here
+ 72 | typedef void (*__sighandler_t) (int);
+ | ^~~~~~~~~~~~~~
+</code></pre>
+<p>
+ Code such as the above relying on a non-zero number of parameters (such
+ as a single <code>int</code>) can be fixed for C23 by adding the correct
+ parameters to the function declarator, such as via:
+</p>
+<pre><code>
+ void (*handler)(int);
+</code></pre>
+<p>
+ In other cases the code is simply missing a <code>#include</code> of
+ the correct header, such as with:
+<pre><code>
+ void *malloc();
+</code></pre>
+<p>
+ These can be fixed by including the correct header and removing the
+ non-prototype declaration.
+</p>
+<p>
+ Alternatively you can use
+ <a
href="https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html#index-std-1";>-std=</a>
+ to select an earlier version of the C standard.
+</p>
<h4 id="c23-new-keywords">New keywords</h4>
<p>
commit 4b61405659dbbfd9312e90e5bf6bfc224eabe3a4
Author: David Malcolm <dmalc...@redhat.com>
Date: Wed Jan 15 14:53:57 2025 -0500
gcc-15/changes: add "C23 by default:" to <li>
Tweak to help readability by adding a prefix to the <li>
diff --git a/htdocs/gcc-15/changes.html b/htdocs/gcc-15/changes.html
index 98d85cf9..171c3db4 100644
--- a/htdocs/gcc-15/changes.html
+++ b/htdocs/gcc-15/changes.html
@@ -101,7 +101,8 @@ a work-in-progress.</p>
<h3 id="c">C</h3>
<ul>
- <li>GCC 15 changes the default language version for C compilation from
+ <li>C23 by default: GCC 15 changes the default language version
+ for C compilation from
<a
href="https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html#index-std-1";>-std=gnu17</a>
to
<a
href="https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html#index-std-1";>-std=gnu23</a>.
-----------------------------------------------------------------------
Summary of changes:
htdocs/gcc-15/changes.html | 3 +-
htdocs/gcc-15/porting_to.html | 64 ++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 65 insertions(+), 2 deletions(-)
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