How to resolve "fpclassify': ambiguous call to overloaded function

I am as new to C++ as someone can be. I have been given the task of installing a simulation, but I keep running into error codes. I was able to resolve most of them, but there is one I am not sure how to tackle.

The error code is C2668, and its description is:

"fpclassify': ambiguous call to overloaded function

Project is "Run Simulation" and File is corecrt_math.h on line 415.

Honestly, I'm not sure if any of the information I have given is of any use, and I'm not sure what information to provide. Maybe it would be better if you could ask me some questions and I can answer them to the best of my ability?

I have included a screenshot of my Visual Studio 19:

^{(Click image to enlarge)}

Reproducible example (demo)

#include <cmath>

int main() {
    std::isnan(1);
}

Expected outcome: That it compiles.

Solution

You probably fed std::fpclassify an integer somehow. Visual Studio has an issue with the integer overloads for the <cmath> functions that manifests itself like in your case instead of casting the integer to a double in accordance with:

c.math.syn#2.2:

[…] if any argument of arithmetic type corresponding to a double parameter has type double or an integer type, then all arguments of arithmetic type corresponding to double parameters are effectively cast to double.

I wrote an error report for std::signbit but it's the same for all <cmath> functions that I've tested and std::fpclassify is one of them - and it's used internally by many other cmath functions.

Line 415 in corecrt_math.h is within the isnan function which calls fpclassify internally.

Steps to fix the problem:

When you build your project you'll get a list of errors in the Error List box. Look for lines showing see reference to function template instantiation 'bool isnan<int>(_Ty) noexcept' being compiled or similar. The <int> part may be any integer type.
Double click that line and the IDE should place the cursor on the call to isnan that is made with an integer.
Replace the isnan(integer) call with isnan(static_cast<double>(integer)).
Repeat these steps for any other cmath functions causing problems.

Note: Using isnan with integers is pointless. isnan(integer) will always return false so a compiler with optimization turned on should replace the whole call with false.