deducer | effective solution for deducing/transforming/reshaping data | Dataset library

This depends entirely on:

1. How much the compiler feels like optimizing the variable away.
2. How you use the variable.

Consider the code you posted. You created a constexpr array. As this is an array, it is 100% legal to index it with a runtime value. This would require the compiler to emit code that accesses the array at that index, which would require that array to actually exist in memory. So if you use it in such a way, it must have storage.

However, since your code only indexes this array with a constant expression index, a compiler that wants to think a bit more than -O0 would allow would realize that it knows the value of all of the elements in that array. So it knows exactly what cArr[0] is. And that means the compiler can just convert that expression into the proper value and just ignore that cArr exists.

Such a compiler could do the same with arr, BTW; it doesn't have to be a constant expression for the compiler to detect a no-op.

Also, note that since both arrays are non-static, neither will take up storage "in the compiled binary". If runtime storage for them is needed, it will be stack space, not executable space.

Broadly speaking, a constexpr variable will take up storage at any reasonable optimization level if you do something that requires it to take up storage. This could be something as innocuous as passing it to a (un-inlined) function that takes the parameter by const&.