如果可能，在编译时检查一个值

Question

I'd like to check a value at compile time, if it's a constexpr value and do run a constexpr form-checking function on it if it is.

Can I do this in c++11/14?

In pseudo code, I'd like to do:

static_if (is_constexpr(x)) 
      static_assert(check(x))

---

Details:

I'm checking a string for a particular format. It's conceptually:

template<std::size_t N>
constexpr bool check(const char (&s)[N]){ return true; }
//^ really a recursive call that checks the string

The constexpr check works with a string literal, but not with a string pointer:

int main(){
  const char* s = "#";
  static_assert(check("#"), "Fmt");; //OK

  //This fails; expectation was it suceeds and the check doesn't run
  static_assert(!is_constexpr(s) || check(s), "Fmt");

}

The is_constexpr is:

#include <type_traits>
template<typename T> 
constexpr typename std::remove_reference<T>::type makeprval(T && t) {
  return t;
}
#define is_constexpr(e) noexcept(makeprval(e))

Answer 1

May be your question is bit unclearer to me. If you want whether a string literal should pass and pointer should not then look at below answer. Should you feel that, I have misunderstood your question then comment it, I shall delete this answer or modify accordingly.

You can use simple C-style macro to check if given variable is a string literal, as I have explained in my answer to below question:
Verify type of string (eg literal, array, pointer) passed to a function

#define IS_LITERAL(X) "" X

The compilation will fail if the X is not a string literal.