将字符转换为无符号整数

Question

I read a huge binary file into a vector of char s.

I need to treat every byte as an unsigned integer(from 0 to 255); and do some arithmetics. How can I convert vector to vector?

---

char a = 227;
cout << a;

prints ?

---

char a = 227;
int b = (int) a;
cout << b << endl;

prints -29

---

char a = 227;
unsigned int b = (unsigned int) a;
cout << b << endl;

prints 4294967267

---

char a = 227;
unsigned char b = (unsigned char) a;
cout << b << endl;

prints ?

Answer 1

std::vector<char> source;
// ... read values into source ...

// Make a copy of source with the chars converted to unsigned chars.
std::vector<unsigned char> destination;
for (const auto s : source) {
  destination.push_back(static_cast<unsigned char>(s))
}

// Examine the values in the new vector.  We cast them to int to get
// the output stream to format it as a number rather than a character.
for (const auto d : destination) {
    std::cout << static_cast<int>(d) << std::endl;
}