How to read entire stream into a std::string?

How about

std::istreambuf_iterator<char> eos;
std::string s(std::istreambuf_iterator<char>(stream), eos);

(could be a one-liner if not for MVP)

post-2011 edit, this approach is now spelled

std::string s(std::istreambuf_iterator<char>(stream), {});

I'm late to the party, but here is a fairly efficient solution:

std::string gulp(std::istream &in)
{
    std::string ret;
    char buffer[4096];
    while (in.read(buffer, sizeof(buffer)))
        ret.append(buffer, sizeof(buffer));
    ret.append(buffer, in.gcount());
    return ret;
}

I did some benchmarking, and it turns out that the std::istreambuf_iterator technique (used by the accepted answer) is actually much slower. On gcc 4.4.5 with -O3, it's about a 4.5x difference on my machine, and the gap becomes wider with lower optimization settings.

You could do

std::string s;
std::ostringstream os;
os<<stream.rdbuf();
s=os.str();

but I don't know if it's more efficient.

Alternative version:

std::string s;
std::ostringstream os;
stream>>os.rdbuf();
s=os.str();