On 2019-03-25 11:58 +0000, Jonny Grant wrote: > Hello! > > On 25/03/2019 11:36, Xi Ruoyao wrote: > > On 2019-03-25 12:11 +0100, Marc Glisse wrote: > > > On Mon, 25 Mar 2019, Jonathan Wakely wrote: > > > > On Sun, 24 Mar 2019, 13:53 Xi Ruoyao, <xry111@xxxxxxxxxxxxxxxx> wrote: > > > > > Well, if you want this to be detected at compile time, maybe you can > > > > > convince > > > > > Jonathan to add an) to > > > > > operator<<(basic_ostream&, > > > > > const char *). Then this case can be detected with "-O -Wnonnull". > > > > > > > > That seems like a good idea. > > > > > > Note that IIRC the attribute is also used for optimization purposes. > > > Adding it would remove the test "if (!__s)". One could try and add the > > > attribute only for user code and not while compiling the library itself, > > > but that's getting complicated (_GLIBCXX_EXTERN_TEMPLATE, specializations > > > for types other than char, etc). > > > > Oh really. I'd been misunderstanding "nonnull" as a pure diagnostic > > attribute > > for long time :(. > > -Wnonnull causes warnings if the implementation checks for NULL. (Unless > -Wno-nonnull-compare is set - which is probably a bad idea) > > Although, g++-8 doesn't give any warning from this, it only seems to > catch directly calling f(NULL); > That's a little limited? It seems so. But for your "cout << p" example -O -Wnonnull works. > Anyway - this is what the warning looks like in practice if the nonnull > attribute is on the function declaration. > > nonnull.cpp: In function ‘void f(int*)’: > nonnull.cpp:8:5: warning: nonnull argument ‘ptr’ compared to NULL > [-Wnonnull-compare] > if(NULL != ptr) > ^~ > I can easily get it past the g++-8 by coping the param locally - is this > suitable though? No. One day the optimizer would optimize it away with some code snip and then we would recevice a bug report (though actually it's not a bug at all since the standard demands p in "operator<<(basic_ostream& os, char * p)" to be not null.) -- Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
