C++ sign extension - c++

Question

I am working on a homework problem, printing from a binary file.
I have searched and found out that my problem is a sign extension problem.
In c the correct action would be to cast to an (unsigned char)
I have tried this solution and it does not work with cout
output with (unsigned) is:
4D 5A FFFFFF90 00 03 00 00 00 04 00 00 00 FFFFFFFF FFFFFFFF 00 00
output with (unsigned char) is:
0M 0Z 0ê 0� 0 0� 0� 0� 0 0� 0� 0� 0ˇ 0ˇ 0� 0�
Any guidance would be most helpful;
Here is the code:
void ListHex(ifstream &inFile)
{
// declare variables
char buf[NUMCHAR];
unsigned char bchar;
while(!inFile.eof())
{
inFile.read(buf,NUMCHAR);
for (int count = 0; count < inFile.gcount(); ++count)
{
cout << setfill('0') << setw(2) << uppercase << hex <<
(unsigned)buf[count] << ' ';
}
cout << '\n';
}
}

Answer 1

How about cout <<setfill('0') << setw(2) << uppercase << hex << (0xFF & buf[count])

Answer 2

void ListHex(std::istream& inFile) {
// declare variables
char c;
while(inFile >> c) {
std::cout << std::setw(2) << std::hex
<< static_cast<int>(c);
}
}
I would recommend do this character by character, the reason being there are all sorts of endian issues I would rather not even think about when dealing with rinterpretive int conversions. The std::ifstream will buffer the chars for you anyway (as will your OS likely too as well).
Notice how we take in the file stream as the more generic std::istream this allows us to pass in any type of istream including std::istringstream, std::cin and std::ifstream.
for example:
ListHex(std::cin);
std::istringstream iss("hello world!");
ListHex(iss);
would hex you user input.
edit
Using a buffer
void ListHex(std::istream& inFile) {
// declare variables
char arr[NUMCHAR];
while(inFile.read(arr, NUMCHAR)) {
for(std::size_t i=0; i!=NUMCHAR; ++i) {
std::cout << std::setw(2) << std::hex
<< static_cast<int>(arr[i]);
}
}
}

Answer 3

You can get rid of the sign extension by masking off the high bits:
(((unsigned) buf[count)) & 0xff)

Answer 4

std::cout prints unsigned char as a character, not an integer. You can perform two casts here – something along the lines of:
static_cast <int> (static_cast <unsigned char> (buf[count]))
Alternatively, use an unsigned char buffer and a single cast:
void ListHext(ifstream& inFile)
{
unsigned char buf[NUMCHAR];
while (inFile.read(reinterpret_cast <char*> (&buf[0]), NUMCHAR))
{
for (int i=0; i < NUMCHAR; ++i)
cout << ... << static_cast <int> (buf[i]) << ' ';
cout << endl;
}
}
Edit:
A mask should not be used here as it assumes a particular character size. The following are equivalent only when CHAR_BIT is 8:
// bad examples
x & 0xFF // note - implicit int conversion
static_cast <int> (x) & 0xFF // note - explicit int conversion
// good example
static_cast <int> (static_cast <unsigned char> (x))