Hi all,
I stumbled over this as I found the wording in the release notes rather
unclear.is.
First, the following gives only a -pedantic warning and not a
-Wflex-array-member-not-at-end:
struct t { int b; int x[]; };
struct q { int b; struct t a[2]; int c; };
warning: invalid use of structure with flexible array member [-Wpedantic]
If I remove the "[2]", it shows additionally:
warning: structure containing a flexible array member is not at the end of
another structure [-Wflex-array-member-not-at-end]
It seems as if it should print latter warning also inside the struct.
Qing? Joseph? Thoughts?
* * *
Secondly, if this is deprecated, shouldn't then the warning enabled by, e.g.,
-Wall or made
otherwise more prominent? (-std=?) - Currently, one either has to find the new
flag or use
-pedantic.
Or is this not really regarded as deprecated? But then (IMHO) we should not
really claim so and just
add the warning without deprecation.
BTW; clang-15 prints the -Wgnu-variable-sized-type-not-at-end warning by
default.
Joseph, all: Thoughts?
* * *
Cross ref: The patch adding the new warning is r14-2197-g070a6bf0bdc6761
https://gcc.gnu.org/pipermail/gcc-cvs/2023-June/385730.html (cf. previously in
this thread)
* * *
Regarding the changes.html wording:
On 07.08.23 16:22, Qing Zhao via Gcc-patches wrote:
Comparing to the 1st version, the only change is to address Richard's
comment on refering a warning option for diagnosing deprecated behavior.
...
+++ 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>.
...
I find the first sentence difficult to read. What do you think of the following?
(It is hard to come up with some good wording.)
--- a/htdocs/gcc-14/changes.html
+++ b/htdocs/gcc-14/changes.html
@@ -31,9 +31,10 @@ a work-in-progress.</p>
<h2>Caveats</h2>
<ul>
<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
+ Support for the GCC extension that a structure containing a C99 flexible
+ array (and any union containing a member of such structure) can be a
+ member of a structure has been deprecated for the case that it is not
+ the last member. 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
Tobias
PS: C17 has:
"A structure or union shall not contain a member with incomplete or function
type (hence, a structure
shall not contain an instance of itself, but may contain a pointer to an
instance of itself), except that
the last member of a structure with more than one named member may have
incomplete array type;
such a structure (and any union containing, possibly recursively, a member
that is such a structure)
shall not be a member of a structure or an element of an array."
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