Using 'auto' type deduction - how to find out what type the compiler deduced?

Question

How can I find out what type the compiler deduced when using the auto keyword?

Example 1: Simpler

auto tickTime = 0.001;

W

Answer 1

Here's a typeid version that uses boost::core::demangle to get the type name at runtime.

#include 
#include 
#include 
#include 
using namespace std::literals;

#include 

template
std::string type_str(){ return boost::core::demangle(typeid(T).name()); }

auto main() -> int{
    auto make_vector = [](auto head, auto ... tail) -> std::vector{
        return {head, tail...};
    };

    auto i = 1;
    auto f = 1.f;
    auto d = 1.0;
    auto s = "1.0"s;
    auto v = make_vector(1, 2, 3, 4, 5);

    std::cout
    << "typeof(i) = " << type_str() << '\n'
    << "typeof(f) = " << type_str() << '\n'
    << "typeof(d) = " << type_str() << '\n'
    << "typeof(s) = " << type_str() << '\n'
    << "typeof(v) = " << type_str() << '\n'
    << std::endl;
}

Which prints this on my system:

typeof(i) = int
typeof(f) = float
typeof(d) = double
typeof(s) = std::__cxx11::basic_string, std::allocator >
typeof(v) = std::vector >