"Null pointer dereference" reported after assert

[Paul Aitken]

Given this code:

void ptr_put(struct whatever *ptr)
{
    assert(ptr);
    assert(ptr->refcnt > 0);

    if (ptr && --ptr->refcnt == 0)
        ptr_destroy(ptr);
}

cppcheck reports null pointer dereferences:

$ cppcheck -q --library=std,gnu,dpdk --enable=unusedFunction,warning /tmp/5a.c
/tmp/5a.c:4:9: warning: Either the condition 'ptr' is redundant or there is possible null pointer dereference: ptr. [nullPointerRedundantCheck]
 assert(ptr->refcnt > 0);
        ^
/tmp/5a.c:6:6: note: Assuming that condition 'ptr' is not redundant
 if (ptr && --ptr->refcnt == 0)
     ^
/tmp/5a.c:4:9: note: Null pointer dereference
 assert(ptr->zif_refcnt > 0);

Nothing is reported when the second assert is removed.

[Paul Aitken]

@danielmarjamaki should a ticket be opend for this issue too?

[Daniel Marjamäki]

Thanks! I have created https://trac.cppcheck.net/ticket/10333

[Christopher Yeleighton]

The following obvious nonsense does not trigger any warning:

void foo ()  { int *r = 0; assert (r); *r = 0; return r; }

It should warn that the assert will always fail and that the following dereference is wrong.