https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109571
Bug ID: 109571
Summary: potential null pointer dereference
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: f.heckenb...@fh-soft.de
Target Milestone: ---
% cat test.cpp
#include <vector>
struct A
{
int i = 0;
};
struct B: A
{
virtual ~B ();
};
struct C
{
std::vector <B *> v;
virtual ~C () { for (A *a: v) a->i++; }
};
int main ()
{
C c;
}
% gcc --std=c++20 -c -Wall -Wnull-dereference -O3 test.cpp
test.cpp: In destructor ‘C::~C()’:
test.cpp:16:36: warning: potential null pointer dereference
[-Wnull-dereference]
16 | virtual ~C () { for (A *a: v) a->i++; }
| ~~~^
test.cpp:16:37: warning: potential null pointer dereference
[-Wnull-dereference]
16 | virtual ~C () { for (A *a: v) a->i++; }
| ~~~~^~
In destructor ‘virtual C::~C()’,
inlined from ‘virtual C::~C()’ at test.cpp:16:41:
test.cpp:16:36: warning: potential null pointer dereference
[-Wnull-dereference]
16 | virtual ~C () { for (A *a: v) a->i++; }
| ~~~^
test.cpp:16:37: warning: potential null pointer dereference
[-Wnull-dereference]
16 | virtual ~C () { for (A *a: v) a->i++; }
|
Of course, strictly speaking any pointer dereference is *potentially* a null
pointer dereference, but there's no particular reason to assume one here. (In
fact, when making v private, the compiler could actually know that v will
always be empty, but still warns.)
Even more stragely, this warning depends on many factors that have nothing to
do with the elements by v being null or not, such as both the calling function
and some function in B being virtual, the for-loop variable being A* (not B*)
etc.
My actual code is of course more complex, so I'd like to understand what's
actually causing this warning, so I can avoid it. (Or should I just disable
it?)
And why is the same warning given 4 times?
