difference in character types

character_types.c

void f0(int x);
void f0(signed int x) {}

void f1(char x);
void f1(signed char x) {}

void f2(char x);
void f2(unsigned char x) {}

void f(char* pc, int* pi)
{
      signed char* psc = pc;
      unsigned char* puc = pc;
      signed int* psi = pi;
}

character_types.cpp

template<typename T, typename >
struct is_same_type { enum { value = false}; };

template<typename T>
struct is_same_type<T,T> { enum { value = true}; };

typedef int assert1[!is_same_type<char, signed char>::value? 1:-1];
typedef int assert2[!is_same_type<char, unsigned char>::value? 1: -1];