[Bug libstdc++/84367] New: [C++11] std::ostringstream stops inserting after multiple call to move assignment operator

[ftingaud at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84367

            Bug ID: 84367
           Summary: [C++11] std::ostringstream stops inserting after
                    multiple call to move assignment operator
           Product: gcc
           Version: 7.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ftingaud at gmail dot com
  Target Milestone: ---

The following code asserts after a few iterations, because oss is no longer
inserting when calling operator<<.
Replacing the move assignment by a clear + str("") works.

#include <sstream>
#include <cassert>
int main()
{
   std::ostringstream oss;
   for (int i = 0; i < 100; ++i) {
      oss << "abc";
      assert(oss.str() == "abc");
      oss = std::ostringstream();
   }
   return 0;
}