7 Expressions [expr]

7.5 Primary expressions [expr.prim]

7.5.1 Literals [expr.prim.literal]

The type of a literal is determined based on its form as specified in [lex.literal].
A string-literal is an lvalue designating a corresponding string literal object ([lex.string]), a user-defined-literal has the same value category as the corresponding operator call expression described in [lex.ext], and any other literal is a prvalue.