Constructing a vector with istream_iterators

Question

I recall once seeing a clever way of using iterators to read an entire binary file into a vector. It looked something like this:

#include 
#i         


        

Answer 1

In C++11 one could:

std::ifstream source("myfile.dat", std::ios::binary);
std::vector<char> data(std::istreambuf_iterator<char>(source), {});

This shorter form avoids the most vexing parse problem because of the {} argument, which removes ambiguity of it being an argument or a formal parameter.

@wilhelmtell's answer could also be updated to avoid this problem by adopting a brace initializer for data. Still in my view, using {} is more simple and turn the initialization form irrelevant.

EDIT

Or, if we had std::lvalue (and maybe std::xvalue instead of std::move):

#include <vector>
#include <fstream>

template <typename T>
constexpr T &lvalue(T &&r) noexcept { return r; }

int main() {
    using namespace std;

    vector<char> data(
        istreambuf_iterator<char>(lvalue(ifstream("myfile.dat", ios::binary))),
        {}
    );
}

Answer 2

You want the std::istreambuf_iterator<>, for raw input. The std::istream_iterator<> is for formatted input. As for the end of the file, use the stream iterator's default constructor.

std::ifstream source("myfile.dat", std::ios::binary);
std::vector<char> data((std::istreambuf_iterator<char>(source)),
                       std::istreambuf_iterator<char>());

Edited to satisfy C++'s most vexing parse. Thanks, @UncleBens.