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    <head>
      <base href="https://bugs.llvm.org/">
    </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 - Calling sync() when rdbuf() is a null pointer should return -1."
   href="https://bugs.llvm.org/show_bug.cgi?id=52155">52155</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Calling sync() when rdbuf() is a null pointer should return -1.
          </td>
        </tr>

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

        <tr>
          <th>Version</th>
          <td>11.0
          </td>
        </tr>

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

        <tr>
          <th>OS</th>
          <td>All
          </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>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>edward.vogel@hpe.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>The Standard doc for the sync() function states:
if rdbuf() is a null pointer, returns -1.

It appears libc++ is missing this check.   

Here's a cut/paste from a cygwin session:

$ cat t1.cpp
#include <istream>
extern "C" int printf(const char *a,...);
using namespace std;
int main() {
  istream x(0);
  int s = x.sync();
  printf("value is %d\n",s);
}

VogelEd@XLB3502Q4E ~/tests
$ clang++  t1.cpp -o a.out

VogelEd@XLB3502Q4E ~/tests
$ ./a.out
value is -1

VogelEd@XLB3502Q4E ~/tests
$ clang++  -stdlib=libc++ t1.cpp -o a.out                                       
VogelEd@XLB3502Q4E ~/tests
$ ./a.out
value is 0


Note that the g++ library gets this right, but libc++ does not.  Visual Studio
2019 also gives the correct answer.

Not a big deal, but I thought I'd post it.

Thanks,

Ed Vogel</pre>
        </div>
      </p>


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