Read a binary file (jpg) to a string using c++

Question

I need to read a jpg file to a string. I want to upload this file to our server, I just find out that the API requires a string as the data of this pic. I followed the sugge

Answer 1

You shouldn't read the file to a string because it is legal for a jpg to contain values that are 0. However in a string, the value 0 has a special meaning (it's the end of string indicator aka \0). You should instead read the file into a vector. You can do this easily like so:

#include <algorithm>
#include <iostream>
#include <fstream>
#include <vector>

int main(int argc, char* argv[])
{
    std::ifstream ifs("C:\\Users\\Borgleader\\Documents\\Rapptz.h");

    if(!ifs)
    {
        return -1;
    }

    std::vector<char> data = std::vector<char>(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());

    //If you really need it in a string you can initialize it the same way as the vector
    std::string data2 = std::string(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());

    std::for_each(data.begin(), data.end(), [](char c) { std::cout << c; });

    std::cin.get();
    return 0;
}

Answer 2

Try opening the file in binary mode:

ifstream fin("cloud.jpg", std::ios::binary);

At a guess, you were probably trying to read the file on Windows and the 61^st character was probably 0x26 -- a control-Z, which (on Windows) will be treated as marking the end of the file.

As far as how to best do the reading, you end up with a choice between simplicity and speed, as demonstrated in a previous answer.

Answer 3

Open the file in binary mode, otherwise it will have funny behavior, and it will handle certain non-text characters in inappropriate ways, at least on Windows.

ifstream fin("cloud.jpg", ios::binary);

Also, instead of a while loop, you can just read the whole file in one shot:

ostrm << fin.rdbuf();