Why no output for constexpr and normal fibonaci

Question

Hi

I thought constexpr is compile time evaluation and fibonaci of 43 with constexpr will be quick compared to non constexpr version

Whats missing here as I am not getting any output?
https://code.sololearn.com/cFR00PH9KfCR/?ref=app

Answer 1

constexpr doesn't necessarily mean that the function *will* be evaluated at compile-time. It just specifies that it *can* be.

You need to make a constexpr variable and assign the result of the function to it, which will force the function to be evaluated at compile time.
https://code.sololearn.com/cvfWYc0CmP84/?ref=app

The error now, as is said in the error message, is because fibonacci<43> exceeds the operation count limit.

The recursive implementation of fibonacci results in a huge number of calls to the fibonacci function (like, a very huge number) since there is no memoization of the function calls AFAIK in GCC.

You can use the iterative approach instead for the calculating the results
https://code.sololearn.com/cAV7dr59LYlm/?ref=app

It works, and as expected, the fibonacciOld() call fails to evaluate in the time limit, while fibonacci1<43>() works just fine

Answer 2

Thanks XXX