Just want to clarify the whole "char" thing

I realise that none of the following types may contain padding bits, and
that all of their bits must take part in value representation:

    signed char
    unsigned char

(As "char" must map to one of the above, this also applies to "char".)

What I would like to clarify however, is the possiblity of a "signed char"
(and thus plain char) having an invalid value, or "trap value".

Below, I reproduce code which prints out an object's bytes by using an
"unsigned char". If I were to change it to "signed char" or plain char,
could the code potentially invoke undefined behaviour?

#include <ostream>

template<class T>
void PrintObjectBytes(T const &obj,std::ostream &os)
{
    unsigned char const * const p_over =
        reinterpret_cast<unsigned char const *>(&obj + 1);

    unsigned char const *p =
        reinterpret_cast<unsigned char const *>(&obj);

    do os << (unsigned)*p++ << " ";
    while(p != p_over);

    os << '\n';
}

#include <iostream>
#include <vector>

int main()
{
    std::vector<double> obj1;

    int obj2[5] = {2,3,4,5,6};

    PrintObjectBytes(obj1, std::cout);
    PrintObjectBytes(obj2, std::cout);
}

--

Frederick Gotham

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