[libc++] Implement LWG 3199

Summary:
The resolution of LWG 3199 makes sure that input-streaming into an empty bitset
does not set the failbit on the input stream.

Reviewers: mclow.lists, EricWF

Subscribers: christof, jkorous, dexonsmith, libcxx-commits

Tags: #libc

Differential Revision: https://reviews.llvm.org/D65105

llvm-svn: 369422

1 files changed, 12 insertions, 0 deletions

diff --git a/libcxx/test/std/utilities/template.bitset/bitset.operators/stream_in.pass.cpp b/libcxx/test/std/utilities/template.bitset/bitset.operators/stream_in.pass.cpp
index 1cb92ea3458..0127b75160b 100644
--- a/libcxx/test/std/utilities/template.bitset/bitset.operators/stream_in.pass.cpp
+++ b/libcxx/test/std/utilities/template.bitset/bitset.operators/stream_in.pass.cpp
@@ -25,6 +25,18 @@ int main(int, char**)
         in >> b;
         assert(b.to_ulong() == 0x5A);
     }
+    {
+        // Make sure that input-streaming an empty bitset does not cause the
+        // failbit to be set (LWG 3199).
+        std::istringstream in("01011010");
+        std::bitset<0> b;
+        in >> b;
+        assert(b.to_string() == "");
+        assert(!in.bad());
+        assert(!in.fail());
+        assert(!in.eof());
+        assert(in.good());
+    }
 #ifndef TEST_HAS_NO_EXCEPTIONS
     {
         std::stringbuf sb;