Best way to check if double equals negative infinity in C++
c++, c++11, numerical, numerical-computing
Solution
`x == -1.0 / 0.0`
This expression evaluates to true iff `x` is negative infinity.
If you are willing to include `cmath`, then `x == - INFINITY` is more readable.
Assuming that floating-point types are mapped to IEEE 754 formats, then each of them has its own infinity. `1.0 / 0.0` is a `double` infinity. It doesn't matter much the type of `INFINITY` because “usual arithmetic conversions” will take care of matching the types of the left- and right-hand-side of `==`.
Problem
I found this: http://en.cppreference.com/w/cpp/numeric/math/isinf but it appears to check for either positive or negative infinity. I just want to check if a value is equal to exactly negative infinity, or in otherwords is log(0) Thanks for answer! Based on response below, here is some code that shows what works. ``` #include <iostream> #include <cmath> #include <math.h> using namespace std; int main() { double c = std::log(0.0); auto result = c == - INFINITY; cout << result << endl; return 0; } ```