Division by a constant or by a variable zero
Consider the following code:
#include <iostream>
int main()
{
double zero = 0;
const double ZERO = 0.;
std::cout << 0/zero << "\n"; // -nan
std::cout << 0/0. << "\n"; // nan
std::cout << 0/ZERO << "\n"; // nan
}
Why 0/zero
does it create -nan
, why is it different from 0/0.
and what is the meaning -nan
?
Demo is here for clang. GCC gives -nan
for all of these cases. Trying to compile with MSVC results in runtime errors for constant values and -nan
for a variable .
Which compiler is more correct in this case?
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From C ++ Standard 5.6.4:
If the second operand / or% is zero, the behavior is undefined.
Subsection 0
causes horrible undefined behavior! This way the compiler is free to do anything, including creating NaN
, writing code that crashes, and raiding your refrigerator. There is no more correct behavior.
For floating point types, C ++ has std::numeric_limits<T>::is_iec559
to check if an implementation supports the IEEE 754 standard for floating point types T
.
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