20 General utilities library [utilities]

20.15 Metaprogramming and type traits [meta]

20.15.11 Constant evaluation context [meta.const.eval]

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constexpr bool is_constant_evaluated() noexcept;
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Returns: true if and only if evaluation of the call occurs within the evaluation of an expression or conversion that is manifestly constant-evaluated ([expr.const]).
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[Example 1: constexpr void f(unsigned char *p, int n) { if (std::is_constant_evaluated()) { // should not be a constexpr if statement for (int k = 0; k<n; ++k) p[k] = 0; } else { memset(p, 0, n); // not a core constant expression } } — end example]