char != signed char && char != unsigned char

char-type.cc

// x86_64-redhat-linux
  
#include <iostream>

template<typename T> struct foo;

#ifndef NO_CHAR
template<> struct foo<char> { void operator()() { std::cout << "char" <<  std::endl;} };
#endif
template<> struct foo<unsigned char> { void operator()() { std::cout << "unsigned char" <<  std::endl;} };
template<> struct foo<signed char> { void operator()() { std::cout << "signed char" <<  std::endl;} };

template<> struct foo<unsigned int> { void operator()() { std::cout << "unsigned ing" <<  std::endl;} };
template<> struct foo<signed int> { void operator()() { std::cout << "signed int" <<  std::endl;} };

int main()
{   

    foo<char>()();              // char or compiletime error if -DNO_CHAR
    foo<unsigned char>()();     // unsigned char
    foo<signed char>()();       // signed char

    foo<int>()();               // unsigned int

    struct { int nothing:1; unsigned int nosign:1; signed int sign:1; } bitfield;

    foo<decltype(bitfield.nothing)>()();    // signed int   (but could be unsigned AFAIK)
    foo<decltype(bitfield.nosign)>()();     // unsigned int
    foo<decltype(bitfield.sign)>()();       // signed int
}