以二进制模式扫描文件并将十六进制字符解释为C ++中的实际数字

Question

I know this title might sound confusing. I have a simple question which I haven't been able to solve yet.

Lets imagine I have a file, opening it with an Hex Editor shows it has two characters inside, say 0x1B and 0x00 (obviously unprintable). I'd like to take that as 1B00 in HEX , which is 6912 in DEC , as opposed to directly converting the characters which would be wrong and is what all other questions I saw asked. Well, thats the task I want to do here. Seems simple, but everything I've tried just does it wrong! Even though I am obviously opening the file in binary mode.

I have only managed to read the characters individually, and mess around a bit, but never do what I actually want, which is as simple as taking those 2 hex characters, interpreting them as an Hex Number, and then convert it to Decimal.

Sorry for any unclear idea, Im not a native speaker. Any help will be appreciated, Im sure you'll think this was quite a noobish question :P

EDIT: Sorry, apparently I didn't explain myself properly. I know this might seem abstract, but it is a really concrete little thing which I have struggled to get solved, yet I haven't been able. Maybe I can ask it another way:

How can I scan a character in binary mode, lets say 0x1B , and convert that to actual 1B characters. Just that.

Answer 1

Sounds like you want to read the file as raw data, and then display it on the screen in decimal? Super easy!

int main() {
    std::ifstream myfile("filename.data", std::ofstream::binary);
    uint16_t number;
    char* buffer = (char*)(&number);
    while(myfile.read(buffer, sizeof(number))) {
        std::cout << number << ' ';
    }
}

The reason it's so easy is that there's no hexidecimal involved. The file is saved as a series of bytes, each byte holds one of 256 values. They aren't hex, they're just a series of values. If you read two bytes into the uint16_t , that is the easiest way to interpret two bytes as a single unsigned 2 byte value. And streaming out a uint16_t will, by default, display that value in decimal. There's no hexidecimal involved. The hexidecimal you saw in the hex editor was because a hex editor interprets the bytes as hex values .

Answer 2

If all you want to do is print a number in hexadecimal form, use std::hex

int i = 0x1B;
std::cout << std::hex << i << std::endl;

Answer 3

std::ifstream infile("test.bin", std::ofstream::binary);

while (true) 
{
    char c1 = ifs.get();
    if (!infile.good())
    {
        break;
    }

    char c2 = ifs.get();
    if (!infile.good())
    {
        break;
    }

    int num = (int)c1 |((int)c2 << 8);

    // if you need the oppisite order then
    // int num = (int)c2 &((int)c1 << 8);
    cout << num;
}