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?
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)
^~
// g++-8 -Wall -Wnonnull -O2 -o nonnull nonnull.cpp
#include <cstddef>
void f(int * ptr) __attribute__((nonnull));
void f(int * ptr)
{
if(NULL != ptr)
{
*ptr = 1;
}
}
int main()
{
int * p = NULL;
f(p);
}
I can easily get it past the g++-8 by coping the param locally - is this
suitable though?
// g++-8 -Wall -Wnonnull -O2 -o nonnull nonnull.cpp
#include <cstddef>
void f(int * ptr) __attribute__((nonnull));
void f(int * ptr)
{
const int * const p = ptr;
if(NULL != p)
{
*ptr = 1;
}
}
int main()
{
int * p = NULL;
f(p);
}
