typeid("") != typeid(const char*)

Question

I'm making a C++ library which relies heavily on RTTI (customizable bridge to another language) and is very confused about string literal type.

This is a simple test I made to show the problem:

std::cout << typeid(const char*).name() << std::endl; // PKc
std::cout << std::any("").type().name() << std::endl; // PKc
std::cout << typeid("").name() << std::endl;          // A1_c

For me it looks like the first two print the type for const char*, but the last one is an array.

Why do results for std::any("").type() and typeid("") differ? Is there a way to get the first behavior, i.e. make results for string literals consistent (I use type identification to call different type handlers)?

P.S.: tests are done using Clang version 8.0.0-3 (tags/RELEASE_800/final) on Ubuntu 19.04.

Answer 1

As others have mentioned, the type of the string literal "" is const char[1], as explained by, e.g., What is the datatype of string literal in C++?.

The type stored in std::any("") is const char* because you are using the following constructor (http://www.eel.is/c++draft/any.cons#8):

// Effects: Constructs an object of type any that contains an object of 
// type std::decay_t<T> direct-initialized with std::forward<T>(value).
template< class T>
any( T&& value );

In this case, T is const char(&)[1] (the type of the string literal ""), and thus std::decay_t<const char(&)[1]> will give you const char*, which is why the typeid() of std::any("").type() is the type ID of const char*.