title: Is there a constexpr version of strstr()?
body: <p>As I understand it, the traditional character array functions, like <code>strlen</code>, <code>strstr</code> etc are all defined by the C-standard, and since <code>constexpr</code> is C++11, they're not declared with it.</p>
  
  <p>However, the <a href="https://en.cppreference.com/w/cpp/string/char_traits" rel="noreferrer">std::char_traits in C++17</a> define some equivalent functions like <a href="https://en.cppreference.com/w/cpp/string/char_traits/find" rel="noreferrer">find</a> (which is essentially a constexpr C++ version of <code>strchr</code>, or <a href="https://en.cppreference.com/w/cpp/string/char_traits/copy" rel="noreferrer">copy</a> which appears to provide something similar to <code>strcpy</code>.</p>
  
  <p>But there's no variant of <code>find</code> that finds a substring, only a single char. So is there some C++ constexpr equivalent of <code>strstr</code> part of the standard anywhere?</p>