Merge master branch.

38 files changed, 169 insertions, 169 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 9e55261a..af264a95 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -164,7 +164,7 @@ nobase_include_HEADERS =                                         \
 lib_LTLIBRARIES = libprotobuf-lite.la libprotobuf.la libprotoc.la
 
 libprotobuf_lite_la_LIBADD = $(PTHREAD_LIBS)
-libprotobuf_lite_la_LDFLAGS = -version-info 16:0:0 -export-dynamic -no-undefined
+libprotobuf_lite_la_LDFLAGS = -version-info 17:0:0 -export-dynamic -no-undefined
 if HAVE_LD_VERSION_SCRIPT
 libprotobuf_lite_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libprotobuf-lite.map
 EXTRA_libprotobuf_lite_la_DEPENDENCIES = libprotobuf-lite.map
@@ -210,7 +210,7 @@ libprotobuf_lite_la_SOURCES =                                  \
   google/protobuf/io/zero_copy_stream_impl_lite.cc
 
 libprotobuf_la_LIBADD = $(PTHREAD_LIBS)
-libprotobuf_la_LDFLAGS = -version-info 16:0:0 -export-dynamic -no-undefined
+libprotobuf_la_LDFLAGS = -version-info 17:0:0 -export-dynamic -no-undefined
 if HAVE_LD_VERSION_SCRIPT
 libprotobuf_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libprotobuf.map
 EXTRA_libprotobuf_la_DEPENDENCIES = libprotobuf.map
@@ -301,7 +301,7 @@ libprotobuf_la_SOURCES =                                       \
 nodist_libprotobuf_la_SOURCES = $(nodist_libprotobuf_lite_la_SOURCES)
 
 libprotoc_la_LIBADD = $(PTHREAD_LIBS) libprotobuf.la
-libprotoc_la_LDFLAGS = -version-info 16:0:0 -export-dynamic -no-undefined
+libprotoc_la_LDFLAGS = -version-info 17:0:0 -export-dynamic -no-undefined
 if HAVE_LD_VERSION_SCRIPT
 libprotoc_la_LDFLAGS += -Wl,--version-script=$(srcdir)/libprotoc.map
 EXTRA_libprotoc_la_DEPENDENCIES = libprotoc.map
diff --git a/src/README.md b/src/README.md
index 3cbeb3e6..4ca9a02a 100644
--- a/src/README.md
+++ b/src/README.md
@@ -1,7 +1,7 @@
 Protocol Buffers - Google's data interchange format
 ===================================================
 
-[![Build Status](https://travis-ci.org/google/protobuf.svg?branch=master)](https://travis-ci.org/google/protobuf) [![Build status](https://ci.appveyor.com/api/projects/status/73ctee6ua4w2ruin?svg=true)](https://ci.appveyor.com/project/protobuf/protobuf)
+[![Build status](https://storage.googleapis.com/protobuf-kokoro-results/status-badge/linux-cpp_distcheck.png)](https://fusion.corp.google.com/projectanalysis/current/KOKORO/prod:protobuf%2Fgithub%2Fmaster%2Fubuntu%2Fcpp_distcheck%2Fcontinuous) [![Build status](https://storage.googleapis.com/protobuf-kokoro-results/status-badge/macos-cpp.png)](https://fusion.corp.google.com/projectanalysis/current/KOKORO/prod:protobuf%2Fgithub%2Fmaster%2Fmacos%2Fcpp%2Fcontinuous) [![Build status](https://storage.googleapis.com/protobuf-kokoro-results/status-badge/macos-cpp_distcheck.png)](https://fusion.corp.google.com/projectanalysis/current/KOKORO/prod:protobuf%2Fgithub%2Fmaster%2Fmacos%2Fcpp_distcheck%2Fcontinuous) [![Build status](https://ci.appveyor.com/api/projects/status/73ctee6ua4w2ruin?svg=true)](https://ci.appveyor.com/project/protobuf/protobuf)
 
 Copyright 2008 Google Inc.
 
diff --git a/src/google/protobuf/any.pb.h b/src/google/protobuf/any.pb.h
index a47000c8..60d2e4cc 100644
--- a/src/google/protobuf/any.pb.h
+++ b/src/google/protobuf/any.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/api.pb.h b/src/google/protobuf/api.pb.h
index 38e43dff..cea0ffe1 100644
--- a/src/google/protobuf/api.pb.h
+++ b/src/google/protobuf/api.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/compiler/plugin.pb.h b/src/google/protobuf/compiler/plugin.pb.h
index 8ccdeae2..55569b5e 100644
--- a/src/google/protobuf/compiler/plugin.pb.h
+++ b/src/google/protobuf/compiler/plugin.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/descriptor.pb.h b/src/google/protobuf/descriptor.pb.h
index b7ef7afc..99d66d00 100644
--- a/src/google/protobuf/descriptor.pb.h
+++ b/src/google/protobuf/descriptor.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/duration.pb.h b/src/google/protobuf/duration.pb.h
index fabc5b00..b66e343a 100644
--- a/src/google/protobuf/duration.pb.h
+++ b/src/google/protobuf/duration.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/empty.pb.h b/src/google/protobuf/empty.pb.h
index 13a4ab0b..7d88bb92 100644
--- a/src/google/protobuf/empty.pb.h
+++ b/src/google/protobuf/empty.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/field_mask.pb.h b/src/google/protobuf/field_mask.pb.h
index 1db37eb2..b46d4997 100644
--- a/src/google/protobuf/field_mask.pb.h
+++ b/src/google/protobuf/field_mask.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/source_context.pb.h b/src/google/protobuf/source_context.pb.h
index d6b45155..5d4dae81 100644
--- a/src/google/protobuf/source_context.pb.h
+++ b/src/google/protobuf/source_context.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/struct.pb.h b/src/google/protobuf/struct.pb.h
index 1ccabb08..7ff4465b 100644
--- a/src/google/protobuf/struct.pb.h
+++ b/src/google/protobuf/struct.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/stubs/bytestream.cc b/src/google/protobuf/stubs/bytestream.cc
index f4af6a50..8df2566a 100644
--- a/src/google/protobuf/stubs/bytestream.cc
+++ b/src/google/protobuf/stubs/bytestream.cc
@@ -113,7 +113,7 @@ char* GrowingArrayByteSink::GetBuffer(size_t* nbytes) {
   ShrinkToFit();
   char* b = buf_;
   *nbytes = size_;
-  buf_ = NULL;
+  buf_ = nullptr;
   size_ = capacity_ = 0;
   return b;
 }
diff --git a/src/google/protobuf/stubs/casts.h b/src/google/protobuf/stubs/casts.h
index 35e2dba0..b509f68c 100644
--- a/src/google/protobuf/stubs/casts.h
+++ b/src/google/protobuf/stubs/casts.h
@@ -89,7 +89,7 @@ inline To down_cast(From* f) {                   // so we only accept pointers
   }
 
 #if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI)
-  assert(f == NULL || dynamic_cast<To>(f) != NULL);  // RTTI: debug mode only!
+  assert(f == nullptr || dynamic_cast<To>(f) != nullptr);  // RTTI: debug mode only!
 #endif
   return static_cast<To>(f);
 }
@@ -107,7 +107,7 @@ inline To down_cast(From& f) {
 
 #if !defined(NDEBUG) && !defined(GOOGLE_PROTOBUF_NO_RTTI)
   // RTTI: debug mode only!
-  assert(dynamic_cast<ToAsPointer>(&f) != NULL);
+  assert(dynamic_cast<ToAsPointer>(&f) != nullptr);
 #endif
   return *static_cast<ToAsPointer>(&f);
 }
diff --git a/src/google/protobuf/stubs/common.cc b/src/google/protobuf/stubs/common.cc
index b54fd1c8..4b65eb89 100644
--- a/src/google/protobuf/stubs/common.cc
+++ b/src/google/protobuf/stubs/common.cc
@@ -175,12 +175,12 @@ void NullLogHandler(LogLevel /* level */, const char* /* filename */,
 static LogHandler* log_handler_ = &DefaultLogHandler;
 static int log_silencer_count_ = 0;
 
-static Mutex* log_silencer_count_mutex_ = NULL;
+static Mutex* log_silencer_count_mutex_ = nullptr;
 GOOGLE_PROTOBUF_DECLARE_ONCE(log_silencer_count_init_);
 
 void DeleteLogSilencerCount() {
   delete log_silencer_count_mutex_;
-  log_silencer_count_mutex_ = NULL;
+  log_silencer_count_mutex_ = nullptr;
 }
 void InitLogSilencerCount() {
   log_silencer_count_mutex_ = new Mutex;
@@ -281,9 +281,9 @@ void LogFinisher::operator=(LogMessage& other) {
 LogHandler* SetLogHandler(LogHandler* new_func) {
   LogHandler* old = internal::log_handler_;
   if (old == &internal::NullLogHandler) {
-    old = NULL;
+    old = nullptr;
   }
-  if (new_func == NULL) {
+  if (new_func == nullptr) {
     internal::log_handler_ = &internal::NullLogHandler;
   } else {
     internal::log_handler_ = new_func;
diff --git a/src/google/protobuf/stubs/common.h b/src/google/protobuf/stubs/common.h
index c5256d32..585e0128 100644
--- a/src/google/protobuf/stubs/common.h
+++ b/src/google/protobuf/stubs/common.h
@@ -101,27 +101,27 @@ namespace internal {
 
 // The current version, represented as a single integer to make comparison
 // easier:  major * 10^6 + minor * 10^3 + micro
-#define GOOGLE_PROTOBUF_VERSION 3006000
+#define GOOGLE_PROTOBUF_VERSION 3006001
 
 // A suffix string for alpha, beta or rc releases. Empty for stable releases.
 #define GOOGLE_PROTOBUF_VERSION_SUFFIX ""
 
 // The minimum library version which works with the current version of the
 // headers.
-#define GOOGLE_PROTOBUF_MIN_LIBRARY_VERSION 3006000
+#define GOOGLE_PROTOBUF_MIN_LIBRARY_VERSION 3006001
 
 // The minimum header version which works with the current version of
 // the library.  This constant should only be used by protoc's C++ code
 // generator.
-static const int kMinHeaderVersionForLibrary = 3006000;
+static const int kMinHeaderVersionForLibrary = 3006001;
 
 // The minimum protoc version which works with the current version of the
 // headers.
-#define GOOGLE_PROTOBUF_MIN_PROTOC_VERSION 3006000
+#define GOOGLE_PROTOBUF_MIN_PROTOC_VERSION 3006001
 
 // The minimum header version which works with the current version of
 // protoc.  This constant should only be used in VerifyVersion().
-static const int kMinHeaderVersionForProtoc = 3006000;
+static const int kMinHeaderVersionForProtoc = 3006001;
 
 // Verifies that the headers and libraries are compatible.  Use the macro
 // below to call this.
diff --git a/src/google/protobuf/stubs/common_unittest.cc b/src/google/protobuf/stubs/common_unittest.cc
index 798a2a27..3ce1c49a 100644
--- a/src/google/protobuf/stubs/common_unittest.cc
+++ b/src/google/protobuf/stubs/common_unittest.cc
@@ -100,14 +100,14 @@ TEST(LoggingTest, DefaultLogging) {
 }
 
 TEST(LoggingTest, NullLogging) {
-  LogHandler* old_handler = SetLogHandler(NULL);
+  LogHandler* old_handler = SetLogHandler(nullptr);
 
   CaptureTestStderr();
   GOOGLE_LOG(INFO   ) << "A message.";
   GOOGLE_LOG(WARNING) << "A warning.";
   GOOGLE_LOG(ERROR  ) << "An error.";
 
-  EXPECT_TRUE(SetLogHandler(old_handler) == NULL);
+  EXPECT_TRUE(SetLogHandler(old_handler) == nullptr);
 
   string text = GetCapturedTestStderr();
   EXPECT_EQ("", text);
@@ -179,9 +179,9 @@ class ClosureTest : public testing::Test {
   virtual void SetUp() {
     current_instance_ = this;
     a_ = 0;
-    b_ = NULL;
+    b_ = nullptr;
     c_.clear();
-    permanent_closure_ = NULL;
+    permanent_closure_ = nullptr;
   }
 
   void DeleteClosureInCallback() {
@@ -196,7 +196,7 @@ class ClosureTest : public testing::Test {
   static ClosureTest* current_instance_;
 };
 
-ClosureTest* ClosureTest::current_instance_ = NULL;
+ClosureTest* ClosureTest::current_instance_ = nullptr;
 
 TEST_F(ClosureTest, TestClosureFunction0) {
   Closure* closure = NewCallback(&SetA123Function);
@@ -321,7 +321,7 @@ TEST_F(ClosureTest, TestPermanentClosureFunction2) {
   EXPECT_EQ(789, a_);
   EXPECT_EQ(cstr, b_);
   a_ = 0;
-  b_ = NULL;
+  b_ = nullptr;
   closure->Run();
   EXPECT_EQ(789, a_);
   EXPECT_EQ(cstr, b_);
@@ -338,7 +338,7 @@ TEST_F(ClosureTest, TestPermanentClosureMethod2) {
   EXPECT_EQ(789, a_);
   EXPECT_EQ(cstr, b_);
   a_ = 0;
-  b_ = NULL;
+  b_ = nullptr;
   closure->Run();
   EXPECT_EQ(789, a_);
   EXPECT_EQ(cstr, b_);
diff --git a/src/google/protobuf/stubs/io_win32.cc b/src/google/protobuf/stubs/io_win32.cc
index 4407facb..f00a268f 100644
--- a/src/google/protobuf/stubs/io_win32.cc
+++ b/src/google/protobuf/stubs/io_win32.cc
@@ -91,7 +91,7 @@ struct CharTraits<wchar_t> {
 
 template <typename char_type>
 bool null_or_empty(const char_type* s) {
-  return s == NULL || *s == 0;
+  return s == nullptr || *s == 0;
 }
 
 // Returns true if the path starts with a drive letter, e.g. "c:".
@@ -225,7 +225,7 @@ bool as_windows_path(const char* path, wstring* result) {
 
 
   if (!is_path_absolute(wpath.c_str())) {
-    int size = ::GetCurrentDirectoryW(0, NULL);
+    int size = ::GetCurrentDirectoryW(0, nullptr);
     if (size == 0 && GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
       return false;
     }
@@ -316,17 +316,17 @@ FILE* fopen(const char* path, const char* mode) {
 #ifdef SUPPORT_LONGPATHS
   if (null_or_empty(path)) {
     errno = EINVAL;
-    return NULL;
+    return nullptr;
   }
   wstring wpath;
   if (!as_windows_path(path, &wpath)) {
     errno = ENOENT;
-    return NULL;
+    return nullptr;
   }
   wstring wmode;
   if (!strings::utf8_to_wcs(mode, &wmode)) {
     errno = EINVAL;
-    return NULL;
+    return nullptr;
   }
   return ::_wfopen(wpath.c_str(), wmode.c_str());
 #else
@@ -365,15 +365,15 @@ bool wcs_to_mbs(const WCHAR* s, string* out, bool outUtf8) {
   BOOL usedDefaultChar = FALSE;
   SetLastError(0);
   int size = WideCharToMultiByte(
-      outUtf8 ? CP_UTF8 : CP_ACP, 0, s, -1, NULL, 0, NULL,
-      outUtf8 ? NULL : &usedDefaultChar);
+      outUtf8 ? CP_UTF8 : CP_ACP, 0, s, -1, nullptr, 0, nullptr,
+      outUtf8 ? nullptr : &usedDefaultChar);
   if ((size == 0 && GetLastError() != ERROR_INSUFFICIENT_BUFFER)
       || usedDefaultChar) {
     return false;
   }
   std::unique_ptr<CHAR[]> astr(new CHAR[size]);
   WideCharToMultiByte(
-      outUtf8 ? CP_UTF8 : CP_ACP, 0, s, -1, astr.get(), size, NULL, NULL);
+      outUtf8 ? CP_UTF8 : CP_ACP, 0, s, -1, astr.get(), size, nullptr, nullptr);
   out->assign(astr.get());
   return true;
 }
@@ -386,7 +386,7 @@ bool mbs_to_wcs(const char* s, wstring* out, bool inUtf8) {
 
   SetLastError(0);
   int size =
-      MultiByteToWideChar(inUtf8 ? CP_UTF8 : CP_ACP, 0, s, -1, NULL, 0);
+      MultiByteToWideChar(inUtf8 ? CP_UTF8 : CP_ACP, 0, s, -1, nullptr, 0);
   if (size == 0 && GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
     return false;
   }
diff --git a/src/google/protobuf/stubs/io_win32_unittest.cc b/src/google/protobuf/stubs/io_win32_unittest.cc
index 9085ed91..6c70d461 100644
--- a/src/google/protobuf/stubs/io_win32_unittest.cc
+++ b/src/google/protobuf/stubs/io_win32_unittest.cc
@@ -112,7 +112,7 @@ void StripTrailingSlashes(string* str) {
 }
 
 bool GetEnvVarAsUtf8(const WCHAR* name, string* result) {
-  DWORD size = ::GetEnvironmentVariableW(name, NULL, 0);
+  DWORD size = ::GetEnvironmentVariableW(name, nullptr, 0);
   if (size > 0 && GetLastError() != ERROR_ENVVAR_NOT_FOUND) {
     std::unique_ptr<WCHAR[]> wcs(new WCHAR[size]);
     ::GetEnvironmentVariableW(name, wcs.get(), size);
@@ -128,7 +128,7 @@ bool GetEnvVarAsUtf8(const WCHAR* name, string* result) {
 }
 
 bool GetCwdAsUtf8(string* result) {
-  DWORD size = ::GetCurrentDirectoryW(0, NULL);
+  DWORD size = ::GetCurrentDirectoryW(0, nullptr);
   if (size > 0) {
     std::unique_ptr<WCHAR[]> wcs(new WCHAR[size]);
     ::GetCurrentDirectoryW(size, wcs.get());
@@ -201,7 +201,7 @@ bool IoWin32Test::CreateAllUnder(wstring path) {
   if (path.find(L"\\\\?\\") != 0) {
     path = wstring(L"\\\\?\\") + path;
   }
-  if (::CreateDirectoryW(path.c_str(), NULL) ||
+  if (::CreateDirectoryW(path.c_str(), nullptr) ||
       GetLastError() == ERROR_ALREADY_EXISTS ||
       GetLastError() == ERROR_ACCESS_DENIED) {
     return true;
@@ -210,7 +210,7 @@ bool IoWin32Test::CreateAllUnder(wstring path) {
     size_t pos = path.find_last_of(L'\\');
     if (pos != wstring::npos) {
       wstring parent(path, 0, pos);
-      if (CreateAllUnder(parent) && CreateDirectoryW(path.c_str(), NULL)) {
+      if (CreateAllUnder(parent) && CreateDirectoryW(path.c_str(), nullptr)) {
         return true;
       }
     }
@@ -352,8 +352,8 @@ TEST_F(IoWin32Test, MkdirTestNonAscii) {
 
   // Create a non-ASCII path.
   // Ensure that we can create the directory using SetCurrentDirectoryW.
-  EXPECT_TRUE(CreateDirectoryW((wtest_tmpdir + L"\\1").c_str(), NULL));
-  EXPECT_TRUE(CreateDirectoryW((wtest_tmpdir + L"\\1\\" + kUtf16Text).c_str(), NULL));
+  EXPECT_TRUE(CreateDirectoryW((wtest_tmpdir + L"\\1").c_str(), nullptr));
+  EXPECT_TRUE(CreateDirectoryW((wtest_tmpdir + L"\\1\\" + kUtf16Text).c_str(), nullptr));
   // Ensure that we can create a very similarly named directory using mkdir.
   // We don't attemp to delete and recreate the same directory, because on
   // Windows, deleting files and directories seems to be asynchronous.
@@ -386,7 +386,7 @@ TEST_F(IoWin32Test, ChdirTestNonAscii) {
   wstring wNonAscii(wtest_tmpdir + L"\\" + kUtf16Text);
   string nonAscii;
   EXPECT_TRUE(strings::wcs_to_utf8(wNonAscii.c_str(), &nonAscii));
-  EXPECT_TRUE(CreateDirectoryW(wNonAscii.c_str(), NULL));
+  EXPECT_TRUE(CreateDirectoryW(wNonAscii.c_str(), nullptr));
   WCHAR cwd[MAX_PATH];
   EXPECT_TRUE(GetCurrentDirectoryW(MAX_PATH, cwd));
   // Ensure that we can cd into the path using SetCurrentDirectoryW.
@@ -400,7 +400,7 @@ TEST_F(IoWin32Test, ChdirTestNonAscii) {
 }
 
 TEST_F(IoWin32Test, AsWindowsPathTest) {
-  DWORD size = GetCurrentDirectoryW(0, NULL);
+  DWORD size = GetCurrentDirectoryW(0, nullptr);
   std::unique_ptr<wchar_t[]> cwd_str(new wchar_t[size]);
   EXPECT_GT(GetCurrentDirectoryW(size, cwd_str.get()), 0);
   wstring cwd = wstring(L"\\\\?\\") + cwd_str.get();
diff --git a/src/google/protobuf/stubs/logging.h b/src/google/protobuf/stubs/logging.h
index f69605d9..f7c6d6a8 100644
--- a/src/google/protobuf/stubs/logging.h
+++ b/src/google/protobuf/stubs/logging.h
@@ -162,7 +162,7 @@ namespace internal {
 template<typename T>
 T* CheckNotNull(const char* /* file */, int /* line */,
                 const char* name, T* val) {
-  if (val == NULL) {
+  if (val == nullptr) {
     GOOGLE_LOG(FATAL) << name;
   }
   return val;
@@ -170,7 +170,7 @@ T* CheckNotNull(const char* /* file */, int /* line */,
 }  // namespace internal
 #define GOOGLE_CHECK_NOTNULL(A) \
   ::google::protobuf::internal::CheckNotNull(\
-      __FILE__, __LINE__, "'" #A "' must not be NULL", (A))
+      __FILE__, __LINE__, "'" #A "' must not be nullptr", (A))
 
 #ifdef NDEBUG
 
@@ -208,7 +208,7 @@ typedef void LogHandler(LogLevel level, const char* filename, int line,
 // also help end users figure out a problem.  If you would prefer that
 // these messages be sent somewhere other than stderr, call SetLogHandler()
 // to set your own handler.  This returns the old handler.  Set the handler
-// to NULL to ignore log messages (but see also LogSilencer, below).
+// to nullptr to ignore log messages (but see also LogSilencer, below).
 //
 // Obviously, SetLogHandler is not thread-safe.  You should only call it
 // at initialization time, and probably not from library code.  If you
diff --git a/src/google/protobuf/stubs/map_util.h b/src/google/protobuf/stubs/map_util.h
index 3e6d381f..2313e1f5 100644
--- a/src/google/protobuf/stubs/map_util.h
+++ b/src/google/protobuf/stubs/map_util.h
@@ -131,7 +131,7 @@ FindWithDefault(const Collection& collection,
 }
 
 // Returns a pointer to the const value associated with the given key if it
-// exists, or NULL otherwise.
+// exists, or nullptr otherwise.
 template <class Collection>
 const typename Collection::value_type::second_type*
 FindOrNull(const Collection& collection,
@@ -156,11 +156,11 @@ FindOrNull(Collection& collection,  // NOLINT
 }
 
 // Returns the pointer value associated with the given key. If none is found,
-// NULL is returned. The function is designed to be used with a map of keys to
+// nullptr is returned. The function is designed to be used with a map of keys to
 // pointers.
 //
 // This function does not distinguish between a missing key and a key mapped
-// to a NULL value.
+// to nullptr.
 template <class Collection>
 typename Collection::value_type::second_type
 FindPtrOrNull(const Collection& collection,
@@ -188,7 +188,7 @@ FindPtrOrNull(Collection& collection,  // NOLINT
 }
 
 // Finds the pointer value associated with the given key in a map whose values
-// are linked_ptrs. Returns NULL if key is not found.
+// are linked_ptrs. Returns nullptr if key is not found.
 template <class Collection>
 typename Collection::value_type::second_type::element_type*
 FindLinkedPtrOrNull(const Collection& collection,
@@ -215,7 +215,7 @@ FindLinkedPtrOrDie(const Collection& collection,
 }
 
 // Finds the value associated with the given key and copies it to *value (if not
-// NULL). Returns false if the key was not found, true otherwise.
+// nullptr). Returns false if the key was not found, true otherwise.
 template <class Collection, class Key, class Value>
 bool FindCopy(const Collection& collection,
               const Key& key,
@@ -447,7 +447,7 @@ LookupOrInsertNew(Collection* const collection,
   std::pair<typename Collection::iterator, bool> ret =
       collection->insert(typename Collection::value_type(
           key,
-          static_cast<typename Collection::value_type::second_type>(NULL)));
+          static_cast<typename Collection::value_type::second_type>(nullptr)));
   if (ret.second) {
     ret.first->second = new Element();
   }
@@ -466,7 +466,7 @@ LookupOrInsertNew(Collection* const collection,
   std::pair<typename Collection::iterator, bool> ret =
       collection->insert(typename Collection::value_type(
           key,
-          static_cast<typename Collection::value_type::second_type>(NULL)));
+          static_cast<typename Collection::value_type::second_type>(nullptr)));
   if (ret.second) {
     ret.first->second = new Element(arg);
   }
@@ -612,7 +612,7 @@ bool UpdateReturnCopy(Collection* const collection,
   return false;
 }
 
-// Tries to insert the given key-value pair into the collection. Returns NULL if
+// Tries to insert the given key-value pair into the collection. Returns nullptr if
 // the insert succeeds. Otherwise, returns a pointer to the existing value.
 //
 // This complements UpdateReturnCopy in that it allows to update only after
@@ -625,7 +625,7 @@ InsertOrReturnExisting(Collection* const collection,
                        const typename Collection::value_type& vt) {
   std::pair<typename Collection::iterator, bool> ret = collection->insert(vt);
   if (ret.second) {
-    return NULL;  // Inserted, no existing previous value.
+    return nullptr;  // Inserted, no existing previous value.
   } else {
     return &ret.first->second;  // Return address of already existing value.
   }
@@ -644,7 +644,7 @@ InsertOrReturnExisting(
 
 // Erases the collection item identified by the given key, and returns the value
 // associated with that key. It is assumed that the value (i.e., the
-// mapped_type) is a pointer. Returns NULL if the key was not found in the
+// mapped_type) is a pointer. Returns nullptr if the key was not found in the
 // collection.
 //
 // Examples:
@@ -665,7 +665,7 @@ typename Collection::value_type::second_type EraseKeyReturnValuePtr(
     const typename Collection::value_type::first_type& key) {
   typename Collection::iterator it = collection->find(key);
   if (it == collection->end()) {
-    return NULL;
+    return nullptr;
   }
   typename Collection::value_type::second_type v = it->second;
   collection->erase(it);
@@ -679,7 +679,7 @@ typename Collection::value_type::second_type EraseKeyReturnValuePtr(
 template <class MapContainer, class KeyContainer>
 void InsertKeysFromMap(const MapContainer& map_container,
                        KeyContainer* key_container) {
-  GOOGLE_CHECK(key_container != NULL);
+  GOOGLE_CHECK(key_container != nullptr);
   for (typename MapContainer::const_iterator it = map_container.begin();
        it != map_container.end(); ++it) {
     key_container->insert(it->first);
@@ -693,7 +693,7 @@ void InsertKeysFromMap(const MapContainer& map_container,
 template <class MapContainer, class KeyContainer>
 void AppendKeysFromMap(const MapContainer& map_container,
                        KeyContainer* key_container) {
-  GOOGLE_CHECK(key_container != NULL);
+  GOOGLE_CHECK(key_container != nullptr);
   for (typename MapContainer::const_iterator it = map_container.begin();
        it != map_container.end(); ++it) {
     key_container->push_back(it->first);
@@ -710,7 +710,7 @@ void AppendKeysFromMap(const MapContainer& map_container,
 template <class MapContainer, class KeyType>
 void AppendKeysFromMap(const MapContainer& map_container,
                        std::vector<KeyType>* key_container) {
-  GOOGLE_CHECK(key_container != NULL);
+  GOOGLE_CHECK(key_container != nullptr);
   // We now have the opportunity to call reserve(). Calling reserve() every
   // time is a bad idea for some use cases: libstdc++'s implementation of
   // vector<>::reserve() resizes the vector's backing store to exactly the
@@ -737,7 +737,7 @@ void AppendKeysFromMap(const MapContainer& map_container,
 template <class MapContainer, class ValueContainer>
 void AppendValuesFromMap(const MapContainer& map_container,
                          ValueContainer* value_container) {
-  GOOGLE_CHECK(value_container != NULL);
+  GOOGLE_CHECK(value_container != nullptr);
   for (typename MapContainer::const_iterator it = map_container.begin();
        it != map_container.end(); ++it) {
     value_container->push_back(it->second);
@@ -754,7 +754,7 @@ void AppendValuesFromMap(const MapContainer& map_container,
 template <class MapContainer, class ValueType>
 void AppendValuesFromMap(const MapContainer& map_container,
                          std::vector<ValueType>* value_container) {
-  GOOGLE_CHECK(value_container != NULL);
+  GOOGLE_CHECK(value_container != nullptr);
   // See AppendKeysFromMap for why this is done.
   if (value_container->empty()) {
     value_container->reserve(map_container.size());
diff --git a/src/google/protobuf/stubs/mutex.h b/src/google/protobuf/stubs/mutex.h
index 47edb7a3..2b1aab87 100644
--- a/src/google/protobuf/stubs/mutex.h
+++ b/src/google/protobuf/stubs/mutex.h
@@ -86,12 +86,12 @@ class LIBPROTOBUF_EXPORT MutexLock {
 typedef MutexLock ReaderMutexLock;
 typedef MutexLock WriterMutexLock;
 
-// MutexLockMaybe is like MutexLock, but is a no-op when mu is NULL.
+// MutexLockMaybe is like MutexLock, but is a no-op when mu is nullptr.
 class LIBPROTOBUF_EXPORT MutexLockMaybe {
  public:
   explicit MutexLockMaybe(Mutex *mu) :
-    mu_(mu) { if (this->mu_ != NULL) { this->mu_->Lock(); } }
-  ~MutexLockMaybe() { if (this->mu_ != NULL) { this->mu_->Unlock(); } }
+    mu_(mu) { if (this->mu_ != nullptr) { this->mu_->Lock(); } }
+  ~MutexLockMaybe() { if (this->mu_ != nullptr) { this->mu_->Unlock(); } }
  private:
   Mutex *const mu_;
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MutexLockMaybe);
@@ -109,7 +109,7 @@ class ThreadLocalStorage {
   }
   T* Get() {
     T* result = static_cast<T*>(pthread_getspecific(key_));
-    if (result == NULL) {
+    if (result == nullptr) {
       result = new T();
       pthread_setspecific(key_, result);
     }
diff --git a/src/google/protobuf/stubs/singleton.h b/src/google/protobuf/stubs/singleton.h
index 2e6ccbdb..5f0f4610 100644
--- a/src/google/protobuf/stubs/singleton.h
+++ b/src/google/protobuf/stubs/singleton.h
@@ -45,7 +45,7 @@ class Singleton {
   }
   static void ShutDown() {
     delete instance_;
-    instance_ = NULL;
+    instance_ = nullptr;
   }
  private:
   static void Init() {
@@ -59,7 +59,7 @@ template<typename T>
 ProtobufOnceType Singleton<T>::once_;
 
 template<typename T>
-T* Singleton<T>::instance_ = NULL;
+T* Singleton<T>::instance_ = nullptr;
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
diff --git a/src/google/protobuf/stubs/statusor.h b/src/google/protobuf/stubs/statusor.h
index 29f869ad..b1c1e6b4 100644
--- a/src/google/protobuf/stubs/statusor.h
+++ b/src/google/protobuf/stubs/statusor.h
@@ -33,7 +33,7 @@
 // usable value, or an error Status explaining why such a value is
 // not present. To this end, StatusOr<T> does not allow its Status
 // value to be Status::OK. Further, StatusOr<T*> does not allow the
-// contained pointer to be NULL.
+// contained pointer to be nullptr.
 //
 // The primary use-case for StatusOr<T> is as the return value of a
 // function which may fail.
@@ -114,15 +114,15 @@ class StatusOr {
   StatusOr(const Status& status);  // NOLINT
 
   // Construct a new StatusOr with the given value. If T is a plain pointer,
-  // value must not be NULL. After calling this constructor, calls to
+  // value must not be nullptr. After calling this constructor, calls to
   // ValueOrDie() will succeed, and calls to status() will return OK.
   //
   // NOTE: Not explicit - we want to use StatusOr<T> as a return type
   // so it is convenient and sensible to be able to do 'return T()'
   // when when the return type is StatusOr<T>.
   //
-  // REQUIRES: if T is a plain pointer, value != NULL. This requirement is
-  // DCHECKed. In optimized builds, passing a NULL pointer here will have
+  // REQUIRES: if T is a plain pointer, value != nullptr. This requirement is
+  // DCHECKed. In optimized builds, passing a null pointer here will have
   // the effect of passing PosixErrorSpace::EINVAL as a fallback.
   StatusOr(const T& value);  // NOLINT
 
@@ -174,13 +174,13 @@ class LIBPROTOBUF_EXPORT StatusOrHelper {
 
 template<typename T>
 struct StatusOrHelper::Specialize {
-  // For non-pointer T, a reference can never be NULL.
+  // For non-pointer T, a reference can never be nullptr.
   static inline bool IsValueNull(const T& t) { return false; }
 };
 
 template<typename T>
 struct StatusOrHelper::Specialize<T*> {
-  static inline bool IsValueNull(const T* t) { return t == NULL; }
+  static inline bool IsValueNull(const T* t) { return t == nullptr; }
 };
 
 }  // namespace internal
@@ -202,7 +202,7 @@ inline StatusOr<T>::StatusOr(const Status& status) {
 template<typename T>
 inline StatusOr<T>::StatusOr(const T& value) {
   if (internal::StatusOrHelper::Specialize<T>::IsValueNull(value)) {
-    status_ = Status(error::INTERNAL, "NULL is not a vaild argument.");
+    status_ = Status(error::INTERNAL, "nullptr is not a vaild argument.");
   } else {
     status_ = Status::OK;
     value_ = value;
diff --git a/src/google/protobuf/stubs/stl_util.h b/src/google/protobuf/stubs/stl_util.h
index 9e4c82a4..2c265e92 100644
--- a/src/google/protobuf/stubs/stl_util.h
+++ b/src/google/protobuf/stubs/stl_util.h
@@ -82,7 +82,7 @@ inline void STLStringResizeUninitialized(string* s, size_t new_size) {
 // already work on all current implementations.
 inline char* string_as_array(string* str) {
   // DO NOT USE const_cast<char*>(str->data())! See the unittest for why.
-  return str->empty() ? NULL : &*str->begin();
+  return str->empty() ? nullptr : &*str->begin();
 }
 
 // STLDeleteElements() deletes all the elements in an STL container and clears
@@ -90,7 +90,7 @@ inline char* string_as_array(string* str) {
 // hash_set, or any other STL container which defines sensible begin(), end(),
 // and clear() methods.
 //
-// If container is NULL, this function is a no-op.
+// If container is nullptr, this function is a no-op.
 //
 // As an alternative to calling STLDeleteElements() directly, consider
 // ElementDeleter (defined below), which ensures that your container's elements
@@ -104,7 +104,7 @@ void STLDeleteElements(T *container) {
 
 // Given an STL container consisting of (key, value) pairs, STLDeleteValues
 // deletes all the "value" components and clears the container.  Does nothing
-// in the case it's given a NULL pointer.
+// in the case it's given a null pointer.
 
 template <class T>
 void STLDeleteValues(T *v) {
diff --git a/src/google/protobuf/stubs/stringpiece.cc b/src/google/protobuf/stubs/stringpiece.cc
index 989474b7..96a7d3da 100644
--- a/src/google/protobuf/stubs/stringpiece.cc
+++ b/src/google/protobuf/stubs/stringpiece.cc
@@ -115,7 +115,7 @@ stringpiece_ssize_type StringPiece::find(char c, size_type pos) const {
   }
   const char* result = static_cast<const char*>(
       memchr(ptr_ + pos, c, length_ - pos));
-  return result != NULL ? result - ptr_ : npos;
+  return result != nullptr ? result - ptr_ : npos;
 }
 
 stringpiece_ssize_type StringPiece::rfind(StringPiece s, size_type pos) const {
diff --git a/src/google/protobuf/stubs/stringpiece.h b/src/google/protobuf/stubs/stringpiece.h
index c7bdd810..6ab985cc 100644
--- a/src/google/protobuf/stubs/stringpiece.h
+++ b/src/google/protobuf/stubs/stringpiece.h
@@ -76,30 +76,30 @@
 //
 // There are several ways to create a null StringPiece:
 //   StringPiece()
-//   StringPiece(NULL)
-//   StringPiece(NULL, 0)
-// For all of the above, sp.data() == NULL, sp.length() == 0,
+//   StringPiece(nullptr)
+//   StringPiece(nullptr, 0)
+// For all of the above, sp.data() == nullptr, sp.length() == 0,
 // and sp.empty() == true.  Also, if you create a StringPiece with
-// a non-NULL pointer then sp.data() != NULL.  Once created,
-// sp.data() will stay either NULL or not-NULL, except if you call
+// a non-null pointer then sp.data() != nullptr.  Once created,
+// sp.data() will stay either nullptr or not-nullptr, except if you call
 // sp.clear() or sp.set().
 //
-// Thus, you can use StringPiece(NULL) to signal an out-of-band value
+// Thus, you can use StringPiece(nullptr) to signal an out-of-band value
 // that is different from other StringPiece values.  This is similar
-// to the way that const char* p1 = NULL; is different from
+// to the way that const char* p1 = nullptr; is different from
 // const char* p2 = "";.
 //
 // There are many ways to create an empty StringPiece:
 //   StringPiece()
-//   StringPiece(NULL)
-//   StringPiece(NULL, 0)
+//   StringPiece(nullptr)
+//   StringPiece(nullptr, 0)
 //   StringPiece("")
 //   StringPiece("", 0)
 //   StringPiece("abcdef", 0)
 //   StringPiece("abcdef"+6, 0)
 // For all of the above, sp.length() will be 0 and sp.empty() will be true.
-// For some empty StringPiece values, sp.data() will be NULL.
-// For some empty StringPiece values, sp.data() will not be NULL.
+// For some empty StringPiece values, sp.data() will be nullptr.
+// For some empty StringPiece values, sp.data() will not be nullptr.
 //
 // Be careful not to confuse: null StringPiece and empty StringPiece.
 // The set of empty StringPieces properly includes the set of null StringPieces.
@@ -109,20 +109,20 @@
 // All empty StringPiece values compare equal to each other.
 // Even a null StringPieces compares equal to a non-null empty StringPiece:
 //  StringPiece() == StringPiece("", 0)
-//  StringPiece(NULL) == StringPiece("abc", 0)
-//  StringPiece(NULL, 0) == StringPiece("abcdef"+6, 0)
+//  StringPiece(nullptr) == StringPiece("abc", 0)
+//  StringPiece(nullptr, 0) == StringPiece("abcdef"+6, 0)
 //
 // Look carefully at this example:
-//   StringPiece("") == NULL
+//   StringPiece("") == nullptr
 // True or false?  TRUE, because StringPiece::operator== converts
-// the right-hand side from NULL to StringPiece(NULL),
+// the right-hand side from nullptr to StringPiece(nullptr),
 // and then compares two zero-length spans of characters.
 // However, we are working to make this example produce a compile error.
 //
 // Suppose you want to write:
-//   bool TestWhat?(StringPiece sp) { return sp == NULL; }  // BAD
+//   bool TestWhat?(StringPiece sp) { return sp == nullptr; }  // BAD
 // Do not do that.  Write one of these instead:
-//   bool TestNull(StringPiece sp) { return sp.data() == NULL; }
+//   bool TestNull(StringPiece sp) { return sp.data() == nullptr; }
 //   bool TestEmpty(StringPiece sp) { return sp.empty(); }
 // The intent of TestWhat? is unclear.  Did you mean TestNull or TestEmpty?
 // Right now, TestWhat? behaves likes TestEmpty.
@@ -207,11 +207,11 @@ class LIBPROTOBUF_EXPORT StringPiece {
   //
   // Style guide exception granted:
   // http://goto/style-guide-exception-20978288
-  StringPiece() : ptr_(NULL), length_(0) {}
+  StringPiece() : ptr_(nullptr), length_(0) {}
 
   StringPiece(const char* str)  // NOLINT(runtime/explicit)
       : ptr_(str), length_(0) {
-    if (str != NULL) {
+    if (str != nullptr) {
       length_ = CheckedSsizeTFromSizeT(strlen(str));
     }
   }
@@ -248,7 +248,7 @@ class LIBPROTOBUF_EXPORT StringPiece {
   bool empty() const { return length_ == 0; }
 
   void clear() {
-    ptr_ = NULL;
+    ptr_ = nullptr;
     length_ = 0;
   }
 
@@ -260,7 +260,7 @@ class LIBPROTOBUF_EXPORT StringPiece {
 
   void set(const char* str) {
     ptr_ = str;
-    if (str != NULL)
+    if (str != nullptr)
       length_ = CheckedSsizeTFromSizeT(strlen(str));
     else
       length_ = 0;
@@ -309,7 +309,7 @@ class LIBPROTOBUF_EXPORT StringPiece {
   // for a StringPiece be called "as_string()".  We also leave the
   // "as_string()" method defined here for existing code.
   string ToString() const {
-    if (ptr_ == NULL) return string();
+    if (ptr_ == nullptr) return string();
     return string(data(), static_cast<size_type>(size()));
   }
 
diff --git a/src/google/protobuf/stubs/stringpiece_unittest.cc b/src/google/protobuf/stubs/stringpiece_unittest.cc
index a6a87595..d9a32d03 100644
--- a/src/google/protobuf/stubs/stringpiece_unittest.cc
+++ b/src/google/protobuf/stubs/stringpiece_unittest.cc
@@ -46,7 +46,7 @@ TEST(StringPiece, Ctor) {
   {
     // Null.
     StringPiece s10;
-    EXPECT_TRUE(s10.data() == NULL);
+    EXPECT_TRUE(s10.data() == nullptr);
     EXPECT_EQ(0, s10.length());
   }
 
@@ -148,8 +148,8 @@ TEST(StringPiece, ComparisonOperators) {
   EXPECT_EQ(result, StringPiece((x)).compare(StringPiece((y))) op 0)
 
   COMPARE(true, ==, "",   "");
-  COMPARE(true, ==, "", NULL);
-  COMPARE(true, ==, NULL, "");
+  COMPARE(true, ==, "", nullptr);
+  COMPARE(true, ==, nullptr, "");
   COMPARE(true, ==, "a",  "a");
   COMPARE(true, ==, "aa", "aa");
   COMPARE(false, ==, "a",  "");
@@ -253,7 +253,7 @@ TEST(StringPiece, STL1) {
 
   EXPECT_EQ(*d.data(), 'f');
   EXPECT_EQ(d.data()[5], 'r');
-  EXPECT_TRUE(e.data() == NULL);
+  EXPECT_TRUE(e.data() == nullptr);
 
   EXPECT_EQ(*a.begin(), 'a');
   EXPECT_EQ(*(b.begin() + 2), 'c');
@@ -312,7 +312,7 @@ TEST(StringPiece, STL2) {
   d.clear();
   EXPECT_EQ(d.size(), 0);
   EXPECT_TRUE(d.empty());
-  EXPECT_TRUE(d.data() == NULL);
+  EXPECT_TRUE(d.data() == nullptr);
   EXPECT_TRUE(d.begin() == d.end());
 
   EXPECT_EQ(StringPiece::npos, string::npos);
@@ -707,17 +707,17 @@ TEST(StringPiece, Contains) {
   EXPECT_TRUE(!a.contains(d));
 }
 
-TEST(StringPiece, NULLInput) {
+TEST(StringPiece, NullInput) {
   // we used to crash here, but now we don't.
-  StringPiece s(NULL);
-  EXPECT_EQ(s.data(), (const char*)NULL);
+  StringPiece s(nullptr);
+  EXPECT_EQ(s.data(), (const char*)nullptr);
   EXPECT_EQ(s.size(), 0);
 
-  s.set(NULL);
-  EXPECT_EQ(s.data(), (const char*)NULL);
+  s.set(nullptr);
+  EXPECT_EQ(s.data(), (const char*)nullptr);
   EXPECT_EQ(s.size(), 0);
 
-  // .ToString() on a StringPiece with NULL should produce the empty string.
+  // .ToString() on a StringPiece with nullptr should produce the empty string.
   EXPECT_EQ("", s.ToString());
   EXPECT_EQ("", s.as_string());
 }
diff --git a/src/google/protobuf/stubs/stringprintf.cc b/src/google/protobuf/stubs/stringprintf.cc
index d98b9b87..820bfe7f 100644
--- a/src/google/protobuf/stubs/stringprintf.cc
+++ b/src/google/protobuf/stubs/stringprintf.cc
@@ -76,7 +76,7 @@ void StringAppendV(string* dst, const char* format, va_list ap) {
       // Error or MSVC running out of space.  MSVC 8.0 and higher
       // can be asked about space needed with the special idiom below:
       va_copy(backup_ap, ap);
-      result = vsnprintf(NULL, 0, format, backup_ap);
+      result = vsnprintf(nullptr, 0, format, backup_ap);
       va_end(backup_ap);
     }
 
diff --git a/src/google/protobuf/stubs/stringprintf_unittest.cc b/src/google/protobuf/stubs/stringprintf_unittest.cc
index 15895e59..7fcbf500 100644
--- a/src/google/protobuf/stubs/stringprintf_unittest.cc
+++ b/src/google/protobuf/stubs/stringprintf_unittest.cc
@@ -91,7 +91,7 @@ TEST(StringPrintfTest, Multibyte) {
   // out of memory while trying to determine destination buffer size.
   // see b/4194543.
 
-  char* old_locale = setlocale(LC_CTYPE, NULL);
+  char* old_locale = setlocale(LC_CTYPE, nullptr);
   // Push locale with multibyte mode
   setlocale(LC_CTYPE, "en_US.utf8");
 
@@ -120,7 +120,7 @@ TEST(StringPrintfTest, Multibyte) {
 
 TEST(StringPrintfTest, NoMultibyte) {
   // No multibyte handling, but the string contains funny chars.
-  char* old_locale = setlocale(LC_CTYPE, NULL);
+  char* old_locale = setlocale(LC_CTYPE, nullptr);
   setlocale(LC_CTYPE, "POSIX");
   string value = StringPrintf("%.*s", 3, "\375\067s");
   setlocale(LC_CTYPE, old_locale);
diff --git a/src/google/protobuf/stubs/strutil.cc b/src/google/protobuf/stubs/strutil.cc
index 65f22a96..5bf9f2e6 100644
--- a/src/google/protobuf/stubs/strutil.cc
+++ b/src/google/protobuf/stubs/strutil.cc
@@ -87,7 +87,7 @@ void StripString(string* s, const char* remove, char replacewith) {
   const char * str_start = s->c_str();
   const char * str = str_start;
   for (str = strpbrk(str, remove);
-       str != NULL;
+       str != nullptr;
        str = strpbrk(str + 1, remove)) {
     (*s)[str - str_start] = replacewith;
   }
@@ -102,7 +102,7 @@ void ReplaceCharacters(string *s, const char *remove, char replacewith) {
   const char *str_start = s->c_str();
   const char *str = str_start;
   for (str = strpbrk(str, remove);
-       str != NULL;
+       str != nullptr;
        str = strpbrk(str + 1, remove)) {
     (*s)[str - str_start] = replacewith;
   }
@@ -280,7 +280,7 @@ static void JoinStringsIterator(const ITERATOR& start,
                                 const ITERATOR& end,
                                 const char* delim,
                                 string* result) {
-  GOOGLE_CHECK(result != NULL);
+  GOOGLE_CHECK(result != nullptr);
   result->clear();
   int delim_length = strlen(delim);
 
@@ -318,7 +318,7 @@ void JoinStrings(const std::vector<string>& components,
 //    result is truncated to 8 bits.
 //
 //    The second call stores its errors in a supplied string vector.
-//    If the string vector pointer is NULL, it reports the errors with LOG().
+//    If the string vector pointer is nullptr, it reports the errors with LOG().
 // ----------------------------------------------------------------------
 
 #define IS_OCTAL_DIGIT(c) (((c) >= '0') && ((c) <= '7'))
@@ -328,12 +328,12 @@ void JoinStrings(const std::vector<string>& components,
 #define LOG_STRING(LEVEL, VECTOR) GOOGLE_LOG_IF(LEVEL, false)
 
 int UnescapeCEscapeSequences(const char* source, char* dest) {
-  return UnescapeCEscapeSequences(source, dest, NULL);
+  return UnescapeCEscapeSequences(source, dest, nullptr);
 }
 
 int UnescapeCEscapeSequences(const char* source, char* dest,
                              std::vector<string> *errors) {
-  GOOGLE_DCHECK(errors == NULL) << "Error reporting not implemented.";
+  GOOGLE_DCHECK(errors == nullptr) << "Error reporting not implemented.";
 
   char* d = dest;
   const char* p = source;
@@ -458,13 +458,13 @@ int UnescapeCEscapeSequences(const char* source, char* dest,
 //    to be the same.
 //
 //    The second call stores its errors in a supplied string vector.
-//    If the string vector pointer is NULL, it reports the errors with LOG().
+//    If the string vector pointer is nullptr, it reports the errors with LOG().
 //
 //    In the first and second calls, the length of dest is returned. In the
 //    the third call, the new string is returned.
 // ----------------------------------------------------------------------
 int UnescapeCEscapeString(const string& src, string* dest) {
-  return UnescapeCEscapeString(src, dest, NULL);
+  return UnescapeCEscapeString(src, dest, nullptr);
 }
 
 int UnescapeCEscapeString(const string& src, string* dest,
@@ -478,7 +478,7 @@ int UnescapeCEscapeString(const string& src, string* dest,
 
 string UnescapeCEscapeString(const string& src) {
   std::unique_ptr<char[]> unescaped(new char[src.size() + 1]);
-  int len = UnescapeCEscapeSequences(src.c_str(), unescaped.get(), NULL);
+  int len = UnescapeCEscapeSequences(src.c_str(), unescaped.get(), nullptr);
   return string(unescaped.get(), len);
 }
 
@@ -982,7 +982,7 @@ static const char two_ASCII_digits[100][2] = {
 
 char* FastUInt32ToBufferLeft(uint32 u, char* buffer) {
   uint32 digits;
-  const char *ASCII_digits = NULL;
+  const char *ASCII_digits = nullptr;
   // The idea of this implementation is to trim the number of divides to as few
   // as possible by using multiplication and subtraction rather than mod (%),
   // and by outputting two digits at a time rather than one.
@@ -1073,7 +1073,7 @@ char* FastInt32ToBufferLeft(int32 i, char* buffer) {
 
 char* FastUInt64ToBufferLeft(uint64 u64, char* buffer) {
   int digits;
-  const char *ASCII_digits = NULL;
+  const char *ASCII_digits = nullptr;
 
   uint32 u = static_cast<uint32>(u64);
   if (u == u64) return FastUInt32ToBufferLeft(u, buffer);
@@ -1231,7 +1231,7 @@ static inline bool IsValidFloatChar(char c) {
 void DelocalizeRadix(char* buffer) {
   // Fast check:  if the buffer has a normal decimal point, assume no
   // translation is needed.
-  if (strchr(buffer, '.') != NULL) return;
+  if (strchr(buffer, '.') != nullptr) return;
 
   // Find the first unknown character.
   while (IsValidFloatChar(*buffer)) ++buffer;
@@ -1286,7 +1286,7 @@ char* DoubleToBuffer(double value, char* buffer) {
   // of a double.  This long double may have extra bits that make it compare
   // unequal to "value" even though it would be exactly equal if it were
   // truncated to a double.
-  volatile double parsed_value = strtod(buffer, NULL);
+  volatile double parsed_value = strtod(buffer, nullptr);
   if (parsed_value != value) {
     int snprintf_result =
       snprintf(buffer, kDoubleToBufferSize, "%.*g", DBL_DIG+2, value);
@@ -1318,7 +1318,7 @@ inline bool CaseEqual(StringPiece s1, StringPiece s2) {
 }
 
 bool safe_strtob(StringPiece str, bool* value) {
-  GOOGLE_CHECK(value != NULL) << "NULL output boolean given.";
+  GOOGLE_CHECK(value != nullptr) << "nullptr output boolean given.";
   if (CaseEqual(str, "true") || CaseEqual(str, "t") ||
       CaseEqual(str, "yes") || CaseEqual(str, "y") ||
       CaseEqual(str, "1")) {
@@ -1619,7 +1619,7 @@ void StrAppend(string *result,
 int GlobalReplaceSubstring(const string& substring,
                            const string& replacement,
                            string* s) {
-  GOOGLE_CHECK(s != NULL);
+  GOOGLE_CHECK(s != nullptr);
   if (s->empty() || substring.empty())
     return 0;
   string tmp;
@@ -1969,7 +1969,7 @@ int Base64UnescapeInternal(const char *src_param, int szsrc,
 //   for (i = 0; i < 255; i += 8) {
 //     for (j = i; j < i + 8; j++) {
 //       pos = strchr(Base64, j);
-//       if ((pos == NULL) || (j == 0))
+//       if ((pos == nullptr) || (j == 0))
 //         idx = -1;
 //       else
 //         idx = pos - Base64;
diff --git a/src/google/protobuf/stubs/strutil.h b/src/google/protobuf/stubs/strutil.h
index d16ffc34..d6bcbc32 100644
--- a/src/google/protobuf/stubs/strutil.h
+++ b/src/google/protobuf/stubs/strutil.h
@@ -285,7 +285,7 @@ inline string JoinStrings(const std::vector<string>& components,
 //
 //    Errors: In the first form of the call, errors are reported with
 //    LOG(ERROR). The same is true for the second form of the call if
-//    the pointer to the string std::vector is NULL; otherwise, error
+//    the pointer to the string std::vector is nullptr; otherwise, error
 //    messages are stored in the std::vector. In either case, the effect on
 //    the dest array is not defined, but rest of the source will be
 //    processed.
@@ -304,7 +304,7 @@ LIBPROTOBUF_EXPORT int UnescapeCEscapeSequences(const char* source, char* dest,
 //    to be the same.
 //
 //    The second call stores its errors in a supplied string vector.
-//    If the string vector pointer is NULL, it reports the errors with LOG().
+//    If the string vector pointer is nullptr, it reports the errors with LOG().
 //
 //    In the first and second calls, the length of dest is returned. In the
 //    the third call, the new string is returned.
diff --git a/src/google/protobuf/stubs/strutil_unittest.cc b/src/google/protobuf/stubs/strutil_unittest.cc
index 6bf0f598..9460a665 100644
--- a/src/google/protobuf/stubs/strutil_unittest.cc
+++ b/src/google/protobuf/stubs/strutil_unittest.cc
@@ -50,18 +50,18 @@ namespace {
 
 TEST(StringUtilityTest, ImmuneToLocales) {
   // Remember the old locale.
-  char* old_locale_cstr = setlocale(LC_NUMERIC, NULL);
-  ASSERT_TRUE(old_locale_cstr != NULL);
+  char* old_locale_cstr = setlocale(LC_NUMERIC, nullptr);
+  ASSERT_TRUE(old_locale_cstr != nullptr);
   string old_locale = old_locale_cstr;
 
   // Set the locale to "C".
-  ASSERT_TRUE(setlocale(LC_NUMERIC, "C") != NULL);
+  ASSERT_TRUE(setlocale(LC_NUMERIC, "C") != nullptr);
 
   EXPECT_EQ("1.5", SimpleDtoa(1.5));
   EXPECT_EQ("1.5", SimpleFtoa(1.5));
 
-  if (setlocale(LC_NUMERIC, "es_ES") == NULL &&
-      setlocale(LC_NUMERIC, "es_ES.utf8") == NULL) {
+  if (setlocale(LC_NUMERIC, "es_ES") == nullptr &&
+      setlocale(LC_NUMERIC, "es_ES.utf8") == nullptr) {
     // Some systems may not have the desired locale available.
     GOOGLE_LOG(WARNING)
       << "Couldn't set locale to es_ES.  Skipping this test.";
diff --git a/src/google/protobuf/stubs/substitute.cc b/src/google/protobuf/stubs/substitute.cc
index 7194a5b1..1ac9ab45 100644
--- a/src/google/protobuf/stubs/substitute.cc
+++ b/src/google/protobuf/stubs/substitute.cc
@@ -44,7 +44,7 @@ using internal::SubstituteArg;
 // to Substitute().
 static int CountSubstituteArgs(const SubstituteArg* const* args_array) {
   int count = 0;
-  while (args_array[count] != NULL && args_array[count]->size() != -1) {
+  while (args_array[count] != nullptr && args_array[count]->size() != -1) {
     ++count;
   }
   return count;
@@ -71,7 +71,7 @@ void SubstituteAndAppend(
     const SubstituteArg& arg6, const SubstituteArg& arg7,
     const SubstituteArg& arg8, const SubstituteArg& arg9) {
   const SubstituteArg* const args_array[] = {
-    &arg0, &arg1, &arg2, &arg3, &arg4, &arg5, &arg6, &arg7, &arg8, &arg9, NULL
+    &arg0, &arg1, &arg2, &arg3, &arg4, &arg5, &arg6, &arg7, &arg8, &arg9, nullptr
   };
 
   // Determine total size needed.
diff --git a/src/google/protobuf/stubs/substitute.h b/src/google/protobuf/stubs/substitute.h
index 7ee442af..e05ca8d8 100644
--- a/src/google/protobuf/stubs/substitute.h
+++ b/src/google/protobuf/stubs/substitute.h
@@ -93,7 +93,7 @@ class SubstituteArg {
 
   // Indicates that no argument was given.
   inline explicit SubstituteArg()
-    : text_(NULL), size_(-1) {}
+    : text_(nullptr), size_(-1) {}
 
   // Primitives
   // We don't overload for signed and unsigned char because if people are
diff --git a/src/google/protobuf/stubs/time.cc b/src/google/protobuf/stubs/time.cc
index 6def637e..a1e5e1e2 100644
--- a/src/google/protobuf/stubs/time.cc
+++ b/src/google/protobuf/stubs/time.cc
@@ -142,12 +142,12 @@ string FormatNanos(int32 nanos) {
 
 // Parses an integer from a null-terminated char sequence. The method
 // consumes at most "width" chars. Returns a pointer after the consumed
-// integer, or NULL if the data does not start with an integer or the
+// integer, or nullptr if the data does not start with an integer or the
 // integer value does not fall in the range of [min_value, max_value].
 const char* ParseInt(const char* data, int width, int min_value,
                      int max_value, int* result) {
   if (!ascii_isdigit(*data)) {
-    return NULL;
+    return nullptr;
   }
   int value = 0;
   for (int i = 0; i < width; ++i, ++data) {
@@ -161,7 +161,7 @@ const char* ParseInt(const char* data, int width, int min_value,
     *result = value;
     return data;
   } else {
-    return NULL;
+    return nullptr;
   }
 }
 
@@ -169,7 +169,7 @@ const char* ParseInt(const char* data, int width, int min_value,
 // "010" will be parsed to 10000000 nanos.
 const char* ParseNanos(const char* data, int32* nanos) {
   if (!ascii_isdigit(*data)) {
-    return NULL;
+    return nullptr;
   }
   int value = 0;
   int len = 0;
@@ -193,15 +193,15 @@ const char* ParseNanos(const char* data, int32* nanos) {
 const char* ParseTimezoneOffset(const char* data, int64* offset) {
   // Accept format "HH:MM". E.g., "08:00"
   int hour;
-  if ((data = ParseInt(data, 2, 0, 23, &hour)) == NULL) {
-    return NULL;
+  if ((data = ParseInt(data, 2, 0, 23, &hour)) == nullptr) {
+    return nullptr;
   }
   if (*data++ != ':') {
-    return NULL;
+    return nullptr;
   }
   int minute;
-  if ((data = ParseInt(data, 2, 0, 59, &minute)) == NULL) {
-    return NULL;
+  if ((data = ParseInt(data, 2, 0, 59, &minute)) == nullptr) {
+    return nullptr;
   }
   *offset = (hour * 60 + minute) * 60;
   return data;
@@ -264,7 +264,7 @@ bool DateTimeToSeconds(const DateTime& time, int64* seconds) {
 void GetCurrentTime(int64* seconds, int32* nanos) {
   // TODO(xiaofeng): Improve the accuracy of this implementation (or just
   // remove this method from protobuf).
-  *seconds = time(NULL);
+  *seconds = time(nullptr);
   *nanos = 0;
 }
 
@@ -290,37 +290,37 @@ bool ParseTime(const string& value, int64* seconds, int32* nanos) {
   //   With UTC offset: 2015-05-20T13:29:35.120-08:00
 
   // Parse year
-  if ((data = ParseInt(data, 4, 1, 9999, &time.year)) == NULL) {
+  if ((data = ParseInt(data, 4, 1, 9999, &time.year)) == nullptr) {
     return false;
   }
   // Expect '-'
   if (*data++ != '-') return false;
   // Parse month
-  if ((data = ParseInt(data, 2, 1, 12, &time.month)) == NULL) {
+  if ((data = ParseInt(data, 2, 1, 12, &time.month)) == nullptr) {
     return false;
   }
   // Expect '-'
   if (*data++ != '-') return false;
   // Parse day
-  if ((data = ParseInt(data, 2, 1, 31, &time.day)) == NULL) {
+  if ((data = ParseInt(data, 2, 1, 31, &time.day)) == nullptr) {
     return false;
   }
   // Expect 'T'
   if (*data++ != 'T') return false;
   // Parse hour
-  if ((data = ParseInt(data, 2, 0, 23, &time.hour)) == NULL) {
+  if ((data = ParseInt(data, 2, 0, 23, &time.hour)) == nullptr) {
     return false;
   }
   // Expect ':'
   if (*data++ != ':') return false;
   // Parse minute
-  if ((data = ParseInt(data, 2, 0, 59, &time.minute)) == NULL) {
+  if ((data = ParseInt(data, 2, 0, 59, &time.minute)) == nullptr) {
     return false;
   }
   // Expect ':'
   if (*data++ != ':') return false;
   // Parse second
-  if ((data = ParseInt(data, 2, 0, 59, &time.second)) == NULL) {
+  if ((data = ParseInt(data, 2, 0, 59, &time.second)) == nullptr) {
     return false;
   }
   if (!DateTimeToSeconds(time, seconds)) {
@@ -330,7 +330,7 @@ bool ParseTime(const string& value, int64* seconds, int32* nanos) {
   if (*data == '.') {
     ++data;
     // Parse nanoseconds.
-    if ((data = ParseNanos(data, nanos)) == NULL) {
+    if ((data = ParseNanos(data, nanos)) == nullptr) {
       return false;
     }
   } else {
@@ -342,14 +342,14 @@ bool ParseTime(const string& value, int64* seconds, int32* nanos) {
   } else if (*data == '+') {
     ++data;
     int64 offset;
-    if ((data = ParseTimezoneOffset(data, &offset)) == NULL) {
+    if ((data = ParseTimezoneOffset(data, &offset)) == nullptr) {
       return false;
     }
     *seconds -= offset;
   } else if (*data == '-') {
     ++data;
     int64 offset;
-    if ((data = ParseTimezoneOffset(data, &offset)) == NULL) {
+    if ((data = ParseTimezoneOffset(data, &offset)) == nullptr) {
       return false;
     }
     *seconds += offset;
diff --git a/src/google/protobuf/timestamp.pb.h b/src/google/protobuf/timestamp.pb.h
index 2800ecdd..88b22b23 100644
--- a/src/google/protobuf/timestamp.pb.h
+++ b/src/google/protobuf/timestamp.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/type.pb.h b/src/google/protobuf/type.pb.h
index dfecb835..b155a8fd 100644
--- a/src/google/protobuf/type.pb.h
+++ b/src/google/protobuf/type.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.
diff --git a/src/google/protobuf/wrappers.pb.h b/src/google/protobuf/wrappers.pb.h
index a7b38162..7e3b7d40 100644
--- a/src/google/protobuf/wrappers.pb.h
+++ b/src/google/protobuf/wrappers.pb.h
@@ -13,7 +13,7 @@
 #error incompatible with your Protocol Buffer headers. Please update
 #error your headers.
 #endif
-#if 3006000 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
+#if 3006001 < GOOGLE_PROTOBUF_MIN_PROTOC_VERSION
 #error This file was generated by an older version of protoc which is
 #error incompatible with your Protocol Buffer headers. Please
 #error regenerate this file with a newer version of protoc.