performance - C++ 11 auto compile time or runtime?

Question

auto a = 10;

When compiler knows a is int, at compile time or at run-time? If it deduce type at run-time, will it not affect performance?

Thanks

Answer 1

Compile time. In C++, runtime type information is stripped during compilation(without RTTI or virtual inheritance). It is not possible, in fact, to inspect the primitive type at runtime.