On 07.08.23 16:22, Qing Zhao via Gcc-patches wrote:
Hi,
This is the 2nd version of the patch.
Comparing to the 1st version, the only change is to address Richard's
comment on refering a warning option for diagnosing deprecated behavior.
Okay for committing?
thanks.
Qing
======
*htdocs/gcc-14/changes.html (Caveats): Add notice about deprecating a C
extension about flexible array members.
---
htdocs/gcc-14/changes.html | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/htdocs/gcc-14/changes.html b/htdocs/gcc-14/changes.html
index dad1ba53..eae25f1a 100644
--- a/htdocs/gcc-14/changes.html
+++ b/htdocs/gcc-14/changes.html
@@ -30,7 +30,18 @@ a work-in-progress.</p>
<!-- .................................................................. -->
<h2>Caveats</h2>
<ul>
- <li>...</li>
+ <li><strong>C:</strong>
+ Support for the GCC extension, a structure containing a C99 flexible
array
+ member, or a union containing such a structure, is not the last field of
+ another structure, is deprecated. Refer to
+ <a href="https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html";>
+ Zero Length Arrays</a>.
+ Any code relying on this extension should be modifed to ensure that
+ C99 flexible array members only end up at the ends of structures.
+ Please use the warning option
+ <a
href="https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wflex-array-member-not-at-end";><code>-Wflex-array-member-not-at-end</code></a>
to
+ identify all such cases in the source code and modify them.
+ </li>
</ul>
I have a question with respect to the static initialization of flexible
array members. According to the documentation this is supported by GCC:
https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
"GCC allows static initialization of flexible array members. This is
equivalent to defining a new structure containing the original structure
followed by an array of sufficient size to contain the data. E.g. in the
following, f1 is constructed as if it were declared like f2.
struct f1 {
int x; int y[];
} f1 = { 1, { 2, 3, 4 } };
struct f2 {
struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } };
"
However, when I compile this code, I get a warning like this:
flex-array.c:6:13: warning: structure containing a flexible array member
is not at the end of another structure [-Wflex-array-member-not-at-end]
6 | struct f1 f1; int data[3];
|
In general, I agree that flexible array members should be at the end,
however the support for static initialization is quite important from my
point of view especially for applications for embedded systems. Here,
dynamic allocations may not be allowed or feasible.
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