This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [patch] Clarify interaction of -Wnarrowing with -std
- From: Jonathan Wakely <jwakely at redhat dot com>
- To: Sandra Loosemore <sandra at codesourcery dot com>
- Cc: Jason Merrill <jason at redhat dot com>, gcc-patches at gcc dot gnu dot org, Gerald Pfeifer <gerald at pfeifer dot com>, Joseph Myers <joseph at codesourcery dot com>
- Date: Tue, 23 Feb 2016 18:39:19 +0000
- Subject: Re: [patch] Clarify interaction of -Wnarrowing with -std
- Authentication-results: sourceware.org; auth=none
- References: <20160219124235 dot GF3171 at redhat dot com> <56C7666F dot 30601 at redhat dot com> <56C7783D dot 2040504 at codesourcery dot com>
On 19/02/16 13:17 -0700, Sandra Loosemore wrote:
On 02/19/2016 12:01 PM, Jason Merrill wrote:
On 02/19/2016 07:42 AM, Jonathan Wakely wrote:
In PR69864 Manu suggests improving the docs to explain that
-Wnarrowing sometimes produces errors not warnings.
I think the right way to do that is clarify how it interacts with
-std. Specifically that the effect of -Wnarrowing listed first in the
manual *only* applies to C++98 modes, For all later modes (not just
with -std=c++11 as it says now), narrowing conversions produce errors
or warnings by default.
OK for trunk?
OK, thanks.
I suppose the patch is OK as it stands, but I was going to suggest
restructuring it so that it talks about the default behavior first and
what it does with non-default -std= options after that, instead of
vice-versa. Unfortunately I am backlogged on other things right now
and it might take me a day or two before I have time to come up with
some alternate wording. If we are in a rush, go ahead and commit the
existing patch meanwhile, I guess.
Is this better?
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 490df93..8d56efa 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -2753,10 +2753,17 @@ During the link-time optimization warn about type mismatches in
global declarations from different compilation units.
Requires @option{-flto} to be enabled. Enabled by default.
-@item -Wnarrowing @r{(C++ and Objective-C++ only)}
+@item -Wno-narrowing @r{(C++ and Objective-C++ only)}
@opindex Wnarrowing
@opindex Wno-narrowing
-With @option{-std=gnu++98} or @option{-std=c++98}, warn when a narrowing
+For C++11 and later standards, narrowing conversions are diagnosed by default,
+as required by the standard. A narrowing conversion from a constant produces
+an error, and a narrowing conversion from a non-constant produces a warning,
+but @option{-Wno-narrowing} suppresses the diagnostic.
+Note that this does not affect the meaning of well-formed code;
+narrowing conversions are still considered ill-formed in SFINAE contexts.
+
+With @option{-Wnarrowing} in C++98, warn when a narrowing
conversion prohibited by C++11 occurs within
@samp{@{ @}}, e.g.
@@ -2766,14 +2773,6 @@ int i = @{ 2.2 @}; // error: narrowing from double to int
This flag is included in @option{-Wall} and @option{-Wc++11-compat}.
-When a later standard is in effect, e.g. when using @option{-std=c++11},
-narrowing conversions are diagnosed by default, as required by the standard.
-A narrowing conversion from a constant produces an error,
-and a narrowing conversion from a non-constant produces a warning,
-but @option{-Wno-narrowing} suppresses the diagnostic.
-Note that this does not affect the meaning of well-formed code;
-narrowing conversions are still considered ill-formed in SFINAE contexts.
-
@item -Wnoexcept @r{(C++ and Objective-C++ only)}
@opindex Wnoexcept
@opindex Wno-noexcept