Make sure to read this post before raising a thread here:
Then tell us:
What language is this for?
CPP
Which rule?
Null pointers should not be dereferenced (cpp:S2259) and so on
Why do you believe it’s a false-positive/false-negative?
The context might be null
Are you using
How can we reproduce the problem? Give us a self-contained snippet (best) or screenshot (good)
CMutexTester.txt (2.3 KB)
Hello, @honghua
void CMutexTester::initialize(CPlugin *plugin, CPluginContext *context)
{
Q_UNUSED(plugin)
// Expectation: sonar prompts you to check that the context pointer is empty before using it
jobMgr = context->getService<IJobManager>();
// Expectation: sonar warns of the risks of null Pointers
jobMgr->addJob(this);
testDeadLock();
writewMapWithAnotherLock();
testMagicNumber();
}
Indeed, context is not guaranteed to point to anything valid, so it might as well be a nullptr. Strictly speaking, this is a false negative.
Yet, such dereferences (with no prior check for nullptr) are used very often in C and in C++ code. And in the majority of the cases they are safe because they rely on some implicit invariant, for example, “this vector contains only non-null pointers” or “this function is called only with non-null arguments”.
Raising an issue for every dereference will introduce a large amount of noise and will annoy an average developer more than it helps them.
For that reason, we only raise an issue if we have a reason to assume that the pointer might be null. For example, this pointer was checked for nullptr before, or it is assigned a null at some point. Arguably, this is a tradeoff between discovery and precision, and Sonar chooses precision and sacrifices some discovery.
That being said, in some safety-critical applications it might make sense to enforce a stricter version of this rule. I’ve created CPP-4078 to keep track of how often this rule is needed. If the request pops up often, we will consider implementing it.
Let me know if something is not clear.