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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">C99 6.8.6.4 p1 says: A return statement without an expression shall only appear in a function whose return type is void.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">So, the bare "return;" in foo() is really an error.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Falling off the end of a non-void function (without an actual "return;" statement) is UB only if the return value is used by the caller.<o:p></o:p></span></p>
<p class="MsoNormal"><a name="_MailEndCompose"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">That is, if you removed the "return;" from foo() and then didn't use its return value in the call from main(), it would be legal.
Although, I'd guess you'd see the same diagnostic as a warning, not an error.<o:p></o:p></span></a></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> cfe-dev [mailto:cfe-dev-bounces@lists.llvm.org]
<b>On Behalf Of </b>David Blaikie via cfe-dev<br>
<b>Sent:</b> Thursday, October 29, 2015 8:10 AM<br>
<b>To:</b> Dan Liew<br>
<b>Cc:</b> Clang Dev<br>
<b>Subject:</b> Re: [cfe-dev] Is -Wno-return-type a warning or error?<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p>Intentional, I believe. We do have some warning which default to being errors. I'm not sure of the specifics of the c language standard in this case, but perhaps there's some case where this is not UB (if the return is never executed, perhaps) so it may
not technically be invalid c.<o:p></o:p></p>
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<p class="MsoNormal">On Oct 29, 2015 4:55 AM, "Dan Liew via cfe-dev" <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Hi,<br>
<br>
I was playing with Clang 3.7 on some old code I noticed that<br>
``-Wreturn-type`` seems to be treated as error.<br>
<br>
For example<br>
<br>
```<br>
int foo() {<br>
int x = 5;<br>
return;<br>
}<br>
<br>
int main() {<br>
int x = foo();<br>
return 0;<br>
}<br>
```<br>
<br>
Now try building<br>
```<br>
$ clang -std=c99 noret.c<br>
noret.c:3:5: error: non-void function 'foo' should return a value<br>
[-Wreturn-type]<br>
return;<br>
^<br>
1 error generated.<br>
```<br>
<br>
It's good that Clang flags up bad code like this but what is confusing<br>
me is the Clang driver is<br>
<br>
* Treating this as an error even though I haven't passed ``-Werror``.<br>
* I can suppress this with ``-Wno-return-type``.<br>
<br>
So I'm not really sure if this is a "warning" or an "error". I expect<br>
<br>
* If it's an "error" then I shouldn't be able to suppress it with the<br>
``-Wno-return-type`` flag.<br>
* If it's a "warning" and I haven't passed ``-Werror`` then Clang<br>
should note the warning but not treat it as an error.<br>
<br>
Is Clang's current (and reasonable) behaviour intentional or this a bug?<br>
<br>
Thanks,<br>
Dan.<br>
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<a href="http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev" target="_blank">http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a><o:p></o:p></p>
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