Reading directly from an std::istream into an std::string

Question

Is there anyway to read a known number of bytes, directly into an std::string, without creating a temporary buffer to do so?

eg currently I can do it by

Answer 1

You could use a combination of copy_n and an insert_iterator

void test_1816319()
{
    static char const* fname = "test_1816319.bin";
    std::ofstream ofs(fname, std::ios::binary);
    ofs.write("\x2\x0", 2);
    ofs.write("ab", 2);
    ofs.close();

    std::ifstream ifs(fname, std::ios::binary);
    std::string s;
    size_t n = 0;
    ifs.read((char*)&n, 2);
    std::istream_iterator isi(ifs), isiend;
    std::copy_n(isi, n, std::insert_iterator(s, s.begin()));
    ifs.close();
    _unlink(fname);

    std::cout << s << std::endl;
}

no copying, no hacks, no possibility of overrun, no undefined behaviour.