C++ show bitmap in hex

Asked Apr 14 '16 at 13:07

Active Apr 14 '16 at 13:15

Viewed 836 times

I am trying to read a bitmap ("sample.bmp") with fstream in C++. Every char of the file should be printed as a decimal and hexadecimal number. But the problem is, that at the 60th character or so the decimal numbers become negative. This is the code snippet I use:

//edit: code fixed

void bitmap::printHeader(std::string filename){
    std::ifstream bmpFile;
    std::vector<char> line;
    util func;
    bmpFile.open(filename, std::ios::binary | std::ios::in);
    bmpFile.seekg(0, std::ios::end);
    std::streampos length = bmpFile.tellg();
    bmpFile.seekg(0, std::ios::beg);
    line.resize(length);
    bmpFile.read(&line[0], length);

    for (int i = 0; i < line.size(); i++){
        std::cout << (int)(UINT8)line[i] << std::endl;
        func.dec2hex((int)(UINT8)line[i]);
    }
    bmpFile.close();
}

The first 60 characters are converted right. After that I get numbers from 0 to -255 which are not representing the right chararcter.

edited Apr 14 '16 at 13:15

asked Apr 14 '16 at 13:07

Moritz W.

1

`char` may be signed. Try using `(int)(unsigned char)line[i]` instead of `(int)line[i]`. – MikeCAT Apr 14 '16 at 13:08
@MikeCAT Or `std::uint8_8` to be more explicit that you are interpreting the value as an integer not a character. – Lingxi Apr 14 '16 at 13:10
Use `uint8_t` is you want a generic unsigned byte. – Some programmer dude Apr 14 '16 at 13:10
std::vector line; -> std::cout << (unsigned int) ... – Exceptyon Apr 14 '16 at 13:12
(int)(UINT8)line[i] worked. Thank you. – Moritz W. Apr 14 '16 at 13:14
Now where is that guy who keeps telling that iostream is not silly but the users are, running into that trap? :) http://stackoverflow.com/questions/2753060/who-architected-designed-cs-iostreams-and-would-it-still-be-considered-wel/16615906#16615906 – BitTickler Apr 14 '16 at 13:38

C++ show bitmap in hex

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