How can i read a 0xFF in a file with libc++ istream_iterator?

Question

Consider the following example code:

#include <iostream>

using namespace std;

int main()
{
  istreambuf_iterator<char> eos;
  istreambuf_iterator<char> iit(cin.rdbuf());
  int i;
  for (i = 0; iit != eos; ++i, ++iit) {
    cout << *iit;
  }
  cout << endl << i << endl;
}

And an input file containing the following: "foo\xffbar":

$ hexdump testin
0000000 66 6f 6f ff 62 61 72
0000007

Now for the test using clang libc++ vs gnu libstdc++:

$ make test
clang++ -std=c++11 -stdlib=libc++ -Wall -stdlib=libc++ -o bug-libcc bug.cpp
clang++ -std=c++11 -stdlib=libc++ -Wall -stdlib=libstdc++ -o bug-libstd bug.cpp
./bug-libcc < testin
foo
3
./bug-libstd < testin
foo�bar
7

As you can see the libc++ version thinks the 0xff is the end of stream and it stops reading. So this leads to a couple of questions.

1) Is this a bug in libc++ that I should report? My google searches for existing bugs have turned up nothing.

2) Is there a good way to work around this issue?

EDIT

The following code works:

#include <iostream>
#include <fstream>

using namespace std;

int main()
{
  ifstream ifs ("testin", ios::binary);
  istreambuf_iterator<char> eos;
  istreambuf_iterator<char> iit(ifs.rdbuf());
  int i;
  for (i = 0; iit != eos; ++i, ++iit) {
    cout << *iit;
  }
  cout << endl << i << endl;
}

Leading me to believe that it is a binary conversion issue, but that doesn't explain why libstdc++ works properly.

EDIT2

Using a file without binary works fine too:

ifstream ifs ("testin");

So there is definitely something fishy going on. It looks like it might be an issue in the implementation of cin though, not the iterator.

Answer 1

Unfortunately there is still a bug in libc++ (in addition to the one ecatmur pointed out). Here is the fix:

Index: include/__std_stream
===================================================================
--- include/__std_stream    (revision 176092)
+++ include/__std_stream    (working copy)
@@ -150,7 +150,7 @@
     {
         for (int __i = __nread; __i > 0;)
         {
-            if (ungetc(__extbuf[--__i], __file_) == EOF)
+            if (ungetc(traits_type::to_int_type(__extbuf[--__i]), __file_) == EOF)
                 return traits_type::eof();
         }
     }

I will get this checked in asap. Sorry for the bug. Thanks for bringing it to my attention.

Fix Committed revision 176822 to the libcxx public svn trunk. The fix requires a re-compiled dylib even though the fix is in a header.