[cfe-dev] Spurious warning about returning reference to lambda capture

[Richard Smith]

On Wed, Nov 20, 2013 at 3:38 PM, Joseph Galbraith <galb at vandyke.com> wrote:

> Hi all,
>
> I'm seeing what I think is a spurious warning from this code:
>
> #include <string>
>
> int
> main(int argc, char**)
> {
>         std::wstring x;
>         auto f = [x] () -> const std::wstring& { return x; };
>
>         return 0;
> }
>
> The warning is:
>
> stack_local.cpp:7:50: warning: reference to stack memory associated with
> local variable 'x' returned [-Wreturn-stack-address]
>         auto f = [x] () -> const std::wstring& { return x; };
>
> I think since x is actually a lambda capture, not a local variable, it is
> okay to return its address (so long as the caller finishes with the address
> before the lambda is destroyed).
>
> (In my particular use case the lambda lifetime is tied to the callers
> lifetime.)
>
> Is my analysis correct?
>
> If so, should we suppress this warning for lambda captures?
>

Yes, and yes. This is llvm.org/PR17374. Patches welcome!


> Thanks,
>
> Joseph
>
> PS. This is from:
>
> cw01:~ galb$ clang++ --version
> Apple LLVM version 5.0 (clang-500.2.79) (based on LLVM 3.3svn)
> Target: x86_64-apple-darwin13.0.0
> Thread model: posix
> _______________________________________________
> cfe-dev mailing list
> cfe-dev at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-dev/attachments/20131120/3fbd2983/attachment.html>