问题
I found here the following "rule":
[...] auto drops const and volatile qualifiers only if they're at the top or right below an outermost reference [...]
I understand that top-level cv-qualifiers are a description of the variable itself (compared to the description of what it is pointing to or referencing). But when is a cv-qualifier "right below an outermost reference" and why would auto drop it (probably the first question answers the second one as well)?
回答1:
"cv right below an outermost reference" means that the reference is to a cv-qualified type. For example, take this function:
const int& foo();
The type "right below the outermost reference" is const int, which means the const is there as well. In this code:
auto i = foo();
the type of i is int, not const int or const int&.
Examples of a constwhich is not right below an outermost reference are:
const char* bar();
const double* volatile & baz();
Using auto to take calls of these functions would deduce to type const char* and const double*, respectively.
来源：https://stackoverflow.com/questions/31492967/cv-qualifiers-of-an-auto-variable