On 2023-01-31 09:11, Qing Zhao wrote:
Update documentation to clarify a GCC extension on structure with
flexible array member being nested in another structure.
gcc/ChangeLog:
* doc/extend.texi: Document GCC extension on a structure containing
a flexible array member to be a member of another structure.
Should this resolve pr#77650 since the proposed action there appears to
be to document these semantics?
Thanks,
Sid
---
gcc/doc/extend.texi | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 4a89a3eae7c..54e4baf49a9 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -1748,7 +1748,40 @@ Flexible array members may only appear as the last
member of a
A structure containing a flexible array member, or a union containing
such a structure (possibly recursively), may not be a member of a
structure or an element of an array. (However, these uses are
-permitted by GCC as extensions.)
+permitted by GCC as extensions, see details below.)
+@end itemize
+
+GCC extension accepts a structure containing a flexible array member, or
+a union containing such a structure (possibly recursively) to be a member
+of a structure.
+
+There are two situations:
+
+@itemize @bullet
+@item
+The structure with a flexible array member is the last field of another
+structure, for example:
+
+@smallexample
+struct flex @{ int length; char data[]; @};
+
+struct out_flex @{ int m; struct flex flex_data; @};
+@end smallexample
+
+In the above, @code{flex_data.data[]} is considered as a flexible array too.
+
+@item
+The structure with a flexible array member is the middle field of another
+structure, for example:
+
+@smallexample
+struct flex @{ int length; char data[]; @};
+
+struct mid_flex @{ int m; struct flex flex_data; int n; @};
+@end smallexample
+
+In the above, @code{flex_data.data[]} is allowed to be extended flexibly to
+the padding. E.g, up to 4 elements.
@end itemize
Non-empty initialization of zero-length
