Apparently missing overload of getline() taking RRef to stream in GCC 4.7.2 and Clang 3.2

问题

I ran into an unexpected compilation error when trying to use getline() with a temporary stream object:

#include <iostream>
#include <string>
#include <sstream>

using namespace std;

int main()
{
    string input = "hello\nworld\nof\ndelimiters";

    string line;
    if (getline(stringstream(input), line)) // ERROR!
    {
        cout << line << endl;
    }
}

It looks like no overload of getline() exists that accepts an rvalue reference to a stream object. If I change main() to use an lvalue, it compiles and runs as expected:

int main()
{
    string input = "hello\nworld\nof\ndelimiters";

    string line;
    stringstream ss(inpupt);
    if (getline(ss, line)) // OK
    {
        cout << line << endl;
    }
}

So I had a look in the C++11 Standard and I found out (§ 21.4.8.9) that an overload of getline() that takes an rvalue reference to a stream object should be present.

Am I missing something obvious, or is this a bug? The error occurs both with GCC 4.7.2 and with Clang 3.2. I cannot test this on VC at the moment.

回答1:

If I compile on OS X with the following line, it compiles successfully. What version of the libstdc++ or libc++ are you using?

clang++ -std=c++11 -stdlib=libc++ foo.cc

libstdc++ (and libc++ for that matter) do not yet fully implement the C++ 2011 standard library. This appears to be one of the missing functions from libstdc++.

Sadly, I don't know of any resource that lists exactly what is missing from each implementation.

来源：https://stackoverflow.com/questions/14574486/apparently-missing-overload-of-getline-taking-rref-to-stream-in-gcc-4-7-2-and