How to read a binary file into a vector of unsigned chars

Lately I've been asked to write a function that reads the binary file into the std::vector<BYTE> where BYTE is an unsigned char. Quite quickly I came with something like this:

#include <fstream>
#include <vector>
typedef unsigned char BYTE;

std::vector<BYTE> readFile(const char* filename)
{
    // open the file:
    std::streampos fileSize;
    std::ifstream file(filename, std::ios::binary);

    // get its size:
    file.seekg(0, std::ios::end);
    fileSize = file.tellg();
    file.seekg(0, std::ios::beg);

    // read the data:
    std::vector<BYTE> fileData(fileSize);
    file.read((char*) &fileData[0], fileSize);
    return fileData;
}

which seems to be unnecessarily complicated and the explicit cast to char* that I was forced to use while calling file.read doesn't make me feel any better about it.

Another option is to use std::istreambuf_iterator:

std::vector<BYTE> readFile(const char* filename)
{
    // open the file:
    std::ifstream file(filename, std::ios::binary);

    // read the data:
    return std::vector<BYTE>((std::istreambuf_iterator<char>(file)),
                              std::istreambuf_iterator<char>());
}

which is pretty simple and short, but still I have to use the std::istreambuf_iterator<char> even when I'm reading into std::vector<unsigned char>.

The last option that seems to be perfectly straightforward is to use std::basic_ifstream<BYTE>, which kinda expresses it explicitly that "I want an input file stream and I want to use it to read BYTEs":

std::vector<BYTE>