<html>
    <head>
      <base href="http://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - failed formatted input overwrites output value"
   href="http://llvm.org/bugs/show_bug.cgi?id=15934">15934</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>failed formatted input overwrites output value
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libc++
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>3.2
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>MacOS X
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>All Bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>hhinnant@apple.com
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>sbn@tbricks.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Hello!

Here is a small test:

#include <sstream>
#include <iostream>

int main()
{
    std::istringstream iss("-a");
    unsigned i = 12345;
    iss >> i;
    std::cout << i << std::endl;
    return 0;
}

When building with clang/libc++ I got the following output:

$ clang++ -stdlib=libc++ a.cpp
$ ./a.out
0
$ clang -v
Apple LLVM version 4.2 (clang-425.0.27) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.3.0
Thread model: posix
$ uname -a
Darwin hostname 12.3.0 Darwin Kernel Version 12.3.0: Sun Jan  6 22:37:10 PST
2013; root:xnu-2050.22.13~1/RELEASE_X86_64 x86_64

In C++ standard (C++03) I can see 22.2.2.1.2p1 [lib.facet.num.get.virtuals]:
"If an error occurs, val is unchanged; otherwise it is set to the resulting
value."</pre>
        </div>
      </p>
      <hr>
      <span>You are receiving this mail because:</span>
      
      <ul>
          <li>You are on the CC list for the bug.</li>
      </ul>
    </body>
</html>