I have the following code:
constexpr unsigned long long power_function(const unsigned long long prime, const unsigned long long iterations) {
return iterations > 0 ? prime * power_function(prime, iterations - 1) : prime;
}
/* Inside my Class Definition*/
private:
static constexpr unsigned long long prime = power_function(-363, 1'000'000); //Error occurs here
IntelliSense complains that power_function
is being used incorrectly. But for the life of me, I can't work out what the issue is. I'm using Visual Studio 2015, FYI.
Error messages:
Error C2131 expression did not evaluate to a constant Basic Server c:\<snip> 28
Error C2131 expression did not evaluate to a constant Basic Server c:\<snip> 33
line 28 corresponds to the line where the return function is, and line 33 corresponds to the line where the constexpr is defined.
There is a recursion limit of 512 for constexpr
in the gcc and clang compilers. Because the compiler interprets constexpr
functions as inline functions (C++ Standard 7.1.5 subsec. 2), they must be resolved at compile time. If after 512 iterations the compiler cannot resolve the expression to a constant, it halts compilation and raises an error. The standard recommends a minimum of 512 for recursive constexpr
function invocations, but does not require it (See Annex B [implimits] 2.38 in the standard).
This limit may be applied in Visual Studio, but I am unsure.
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