Fix warning C4701: "potentially uninitialized local variable used"

[fsb4000]

Hello.
I tried to use your library (1.86.0) and I faced with an issue. I didn't have the issue with 1.85.0.
I use VS 2022 and I get an error.

boost-math\include\boost\math\special_functions\detail\bessel_ik.hpp(417) : error C2220: the following warning is treated as an error
boost-math\include\boost\math\special_functions\detail\bessel_ik.hpp(417) : warning C4701: potentially uninitialized local variable 'n' used
boost-math\include\boost\math\special_functions\detail\bessel_ik.hpp(417) : warning C4701: potentially uninitialized local variable 'u' used

As you can see we initialize n and u only in the else branch and later we use them in if (reflect). We might not get into this if if we haven't been in that else but the compiler don't know about it. I tried to fix the issue.

[ckormanyos]

Cool find. I'll try to maybe find/add a test case that hits the lines?

[ckormanyos]

Cool find. I'll try to maybe find/add a test case that hits the lines?

Wait a sec, ...

According to the covrage report, the lines are being hit. Is there maybe a better fix? Delay declaration of the variables or static_cast<void>?

[jzmaddock]

I would need to double check, but I seem to remember fixing this while doing some code-coverage work. Ah, yes it is, see: https://github.com/boostorg/math/blob/develop/include/boost/math/special_functions/detail/bessel_ik.hpp

[ckormanyos]

I think you can declare n and u at lines 340'and 341? Isn't that the point of the warning?

[fsb4000]

I think you can declare n and u at lines 340'and 341? Isn't that the point of the warning?

They are used not only in the else but later in another if.

math/include/boost/math/special_functions/detail/bessel_ik.hpp

Lines 338 to 341 in 5a4f8ba

	else
	{
	n = iround(v, pol);
	u = v - n; // -1/2 <= u < 1/2

math/include/boost/math/special_functions/detail/bessel_ik.hpp

Lines 415 to 417 in 5a4f8ba

	if (reflect)
	{
	T z = (u + n % 2);

Ok, I will try to create a test case...

[fsb4000]

I found a test case for that:

boost::math::cyl_bessel_k(-1.25, std::numeric_limits<double>::infinity());

Where can I find what result should be for this?
I added

std::cout << "v = " << v<< " x = " << x << " kind = " << kind << " reflect = " << reflect <<std::endl;
std::cout << "u = " << u << " n = " << n << std::endl;

before T z = (u + n % 2); and I got(for version without my changes):

v = 1.25 x = inf kind = 2 reflect = 1
u = 3.18226e-312 n = 4147116544 // I belive they are not initialized.

the call result was 0
What is the real result should be?
Where do you add warning options? Sorry I'm not experienced with b2.

[fsb4000]

I found a way to fail for that case( BOOST_MATH_ASSERT(fabs(v - n - u) < tools::forth_root_epsilon<T>());). And I think I found a more correct fix: calculate n and u before the if.
I would also add the warning C4701 to your CI(and treat the warning as an error) but I don't know what to add to https://github.com/boostorg/math/blob/develop/.github/workflows/ci.yml for toolset: [ msvc-14.2 ]

[jzmaddock]

My bad, you are correct that this is NOT fixed in develop, but IS in this branch/PR: #1111 that is still at least somewhat work in progress. I would prefer not to create two competing fixes if possible, as the coverage test branch will be merged fairly soon anyway. Please leave this open and I'll take a look at your test case once I get some time (which will be a couple of weeks).