[PDF] constexpr c string concatenation

How do I return a char array from constexpr?

You MUST know the size of the char array to return it from constexpr and even then you have to trick it since you cannot simply return char* from that. It is much simpler to create a macro which will expand to the char* what you need. From constexpr you cannot return char* which is constructed there...

Is constexpr a legal function?

Nope, for constexpr you need a legal function in the first place, and functions can't do pasting etc. of string literal arguments. If you think about the equivalent expression in a regular function, it would be allocating memory and concatenating the strings - definitely not amenable to constexpr.

How is concatenation implemented in JavaScript?

In that library, concatenation is implemented by turning the string literal into a variadic template argument pack of chars and then unpacking it as a sequence of chars that brace-initialize an array of chars of the same size.

Can a constexpr FCT a function that contains both strings?

Constexpr are evaluated later (ref?). ( f (x) f (y) where f is a function is a syntax error afaik) But you can return from your constexpr fct an object of some other type (with a constexpr ctor or that is an aggregate) that contains both strings and can be inserted/printed into an basic_ostream. Edit: here's the example.