Consider the following code:

#include <typeinfo>
struct S
{
    unsigned int n4  :  4;
    unsigned int n12 : 12;
};

void f(unsigned char)
{
    std::cout << "uc" << std::endl;
}

void f(unsigned short)
{
    std::cout << "us" << std::endl;
}

void f(unsigned int)
{
    std::cout << "ui" << std::endl;
}

int main(int argc, char* argv[])
{
    S s; s.n4 = 0; s.n12 = 0;
    f(s.n4);
    f(s.n12);
    std::cout << typeid(s.n4).name() << std::endl;
    std::cout << typeid(s.n12).name() << std::endl;
    std::cout << typeid(unsigned char).name() << std::endl;
    std::cout << typeid(unsigned short).name() << std::endl;
    std::cout << typeid(unsigned int).name() << std::endl;
    return 0;
}

Expected output (according to standard [class.bit] (http://eel.is/c++draft/class.bit): "The bit-field attribute is not part of the type of the class member."):

ui
ui
j
j
h
t
j

Output produced with g++ (Ubuntu 8.1.0-5ubuntu1~16.04) 8.1.0 (initially discovered with 5.5.0):

ui
ui
h
t
h
t
j

So while the overload is selected correctly, typeid selects the bad type.

I did not test separately, but assume the compiler showing same behaviour for C as well.