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c++constexprequivalent

Is `const constexpr` on variables redundant?

cppreference states that:

A constexpr specifier used in an object declaration or non-static member function (until C++14) implies const.

Does "object declaration" mean "any variable declaration"?

I.e. is

constexpr const int someConstant = 3;

equivalent to

constexpr int someConstant = 3;

in C++11, C++14 and C++17?

Solution

  • In declarations with primitives, such as the one in your example, const is indeed redundant. However, there may be odd situations where const would be required, for example

    constexpr int someConstant = 3;
constexpr const int *someConstantPointerToConstant = &someConstant;

    Here, someConstantPointerToConstant is both a constexpr (i.e. it's known at compile time, hence constexpr) and it is also a pointer to constant (i.e. its object cannot be changed, hence const). The second declaration above would not compile with const omitted (demo).