diff --git a/src/AbstractBtMessage.cc b/src/AbstractBtMessage.cc
index 39dd13e9..76eb4787 100644
--- a/src/AbstractBtMessage.cc
+++ b/src/AbstractBtMessage.cc
@@ -45,11 +45,11 @@ AbstractBtMessage::AbstractBtMessage(uint8_t id, const char* name)
     uploading_(false),
     cuid_(0),
     name_(name),
-    pieceStorage_(0),
-    dispatcher_(0),
-    messageFactory_(0),
-    requestFactory_(0),
-    peerConnection_(0),
+    pieceStorage_(nullptr),
+    dispatcher_(nullptr),
+    messageFactory_(nullptr),
+    requestFactory_(nullptr),
+    peerConnection_(nullptr),
     metadataGetMode_(false)
 {}
 
diff --git a/src/AbstractDiskWriter.cc b/src/AbstractDiskWriter.cc
index 2e5a5357..a8a7f931 100644
--- a/src/AbstractDiskWriter.cc
+++ b/src/AbstractDiskWriter.cc
@@ -64,7 +64,7 @@ AbstractDiskWriter::AbstractDiskWriter(const std::string& filename)
 #endif // !__MINGW32__
     readOnly_(false),
     enableMmap_(false),
-    mapaddr_(0),
+    mapaddr_(nullptr),
     maplen_(0)
 
 {}
@@ -155,7 +155,7 @@ void AbstractDiskWriter::closeFile()
     } else {
       A2_LOG_INFO(fmt("Unmapping file %s succeeded", filename_.c_str()));
     }
-    mapaddr_ = 0;
+    mapaddr_ = nullptr;
     maplen_ = 0;
   }
 #endif // HAVE_MMAP || defined __MINGW32__
@@ -356,7 +356,7 @@ void AbstractDiskWriter::ensureMmapWrite(size_t len, int64_t offset)
           A2_LOG_ERROR(fmt("Unmapping file %s failed: %s",
                            filename_.c_str(), fileStrerror(errNum).c_str()));
         }
-        mapaddr_ = 0;
+        mapaddr_ = nullptr;
         maplen_ = 0;
         enableMmap_ = false;
       }
@@ -381,7 +381,7 @@ void AbstractDiskWriter::ensureMmapWrite(size_t len, int64_t offset)
         }
 #else // !__MINGW32__
         mapaddr_ = reinterpret_cast<unsigned char*>
-          (mmap(0, size(), PROT_READ | PROT_WRITE, MAP_SHARED, fd_, 0));
+          (mmap(nullptr, size(), PROT_READ | PROT_WRITE, MAP_SHARED, fd_, 0));
         if(!mapaddr_) {
           errNum = errno;
         }
diff --git a/src/AppleTLSContext.cc b/src/AppleTLSContext.cc
index 939caa39..315d051e 100644
--- a/src/AppleTLSContext.cc
+++ b/src/AppleTLSContext.cc
@@ -102,7 +102,7 @@ namespace {
   std::string errToString(OSStatus err)
   {
     std::string rv = "Unkown error";
-    CFStringRef cerr = SecCopyErrorMessageString(err, 0);
+    CFStringRef cerr = SecCopyErrorMessageString(err, nullptr);
     if (cerr) {
       size_t len = CFStringGetLength(cerr) * 4;
       char *buf = new char[len];
@@ -118,7 +118,7 @@ namespace {
   bool checkIdentity(const SecIdentityRef id, const std::string& fingerPrint,
                      const std::vector<std::string> supported)
   {
-    SecCertificateRef ref = 0;
+    SecCertificateRef ref = nullptr;
     if (SecIdentityCopyCertificate(id, &ref) != errSecSuccess) {
       A2_LOG_ERROR("Failed to get a certref!");
       return false;
@@ -155,7 +155,7 @@ AppleTLSContext::~AppleTLSContext()
 {
   if (credentials_) {
     CFRelease(credentials_);
-    credentials_ = 0;
+    credentials_ = nullptr;
   }
 }
 
@@ -198,7 +198,7 @@ bool AppleTLSContext::tryAsFingerprint(const std::string& fingerprint)
   A2_LOG_DEBUG(fmt("Looking for cert with fingerprint %s", fp.c_str()));
 
   // Build and run the KeyChain the query.
-  SecPolicyRef policy = SecPolicyCreateSSL(true, 0);
+  SecPolicyRef policy = SecPolicyCreateSSL(true, nullptr);
   if (!policy) {
     A2_LOG_ERROR("Failed to create SecPolicy");
     return false;
@@ -210,8 +210,8 @@ bool AppleTLSContext::tryAsFingerprint(const std::string& fingerprint)
     policy,
     kSecMatchLimitAll
   };
-  CFDictionaryRef query = CFDictionaryCreate(0, query_keys, query_values,
-                                             4, 0, 0);
+  CFDictionaryRef query = CFDictionaryCreate(nullptr, query_keys, query_values,
+                                             4, nullptr, nullptr);
   if (!query) {
     A2_LOG_ERROR("Failed to create identity query");
     return false;
diff --git a/src/AppleTLSContext.h b/src/AppleTLSContext.h
index e5c7cbba..d69968a2 100644
--- a/src/AppleTLSContext.h
+++ b/src/AppleTLSContext.h
@@ -51,7 +51,7 @@ public:
   AppleTLSContext(TLSSessionSide side)
     : side_(side),
       verifyPeer_(true),
-      credentials_(0)
+      credentials_(nullptr)
   {}
 
   virtual ~AppleTLSContext();
diff --git a/src/AppleTLSSession.cc b/src/AppleTLSSession.cc
index c34c7fa8..d34282ec 100644
--- a/src/AppleTLSSession.cc
+++ b/src/AppleTLSSession.cc
@@ -295,7 +295,7 @@ TLSSession* TLSSession::make(TLSContext* ctx)
 
 AppleTLSSession::AppleTLSSession(AppleTLSContext* ctx)
   : ctx_(ctx),
-    sslCtx_(0),
+    sslCtx_(nullptr),
     sockfd_(0),
     state_(st_constructed),
     lastError_(noErr),
@@ -343,7 +343,7 @@ AppleTLSSession::AppleTLSSession(AppleTLSContext* ctx)
       state_ = st_error;
       return;
     }
-    CFArrayRef certs = CFArrayCreate(0, (const void**)&creds, 1, 0);
+    CFArrayRef certs = CFArrayCreate(nullptr, (const void**)&creds, 1, nullptr);
     if (!certs) {
       A2_LOG_ERROR("AppleTLS: Failed to setup credentials");
       state_ = st_error;
@@ -374,7 +374,7 @@ AppleTLSSession::~AppleTLSSession()
   closeConnection();
   if (sslCtx_) {
     SSLDisposeContext(sslCtx_);
-    sslCtx_ = 0;
+    sslCtx_ = nullptr;
   }
   state_ = st_error;
 }
@@ -448,7 +448,7 @@ ssize_t AppleTLSSession::writeData(const void* data, size_t len)
   }
   size_t processed = 0;
   if (writeBuffered_) {
-    lastError_ = SSLWrite(sslCtx_, 0, 0, &processed);
+    lastError_ = SSLWrite(sslCtx_, nullptr, 0, &processed);
     switch (lastError_) {
       case noErr:
         processed = writeBuffered_;
diff --git a/src/AsyncNameResolver.cc b/src/AsyncNameResolver.cc
index 8cdee30e..048f7377 100644
--- a/src/AsyncNameResolver.cc
+++ b/src/AsyncNameResolver.cc
@@ -148,21 +148,21 @@ ares_addr_node* parseAsyncDNSServers(const std::string& serversOpt)
               ',',
               true /* doStrip */);
   ares_addr_node root;
-  root.next = 0;
+  root.next = nullptr;
   ares_addr_node* tail = &root;
-  ares_addr_node* node = 0;
+  ares_addr_node* node = nullptr;
   for(std::vector<std::string>::const_iterator i = servers.begin(),
         eoi = servers.end(); i != eoi; ++i) {
-    if(node == 0) {
+    if(node == nullptr) {
       node = new ares_addr_node();
     }
     size_t len = net::getBinAddr(&node->addr, (*i).c_str());
     if(len != 0) {
-      node->next = 0;
+      node->next = nullptr;
       node->family = (len == 4 ? AF_INET : AF_INET6);
       tail->next = node;
       tail = node;
-      node = 0;
+      node = nullptr;
     }
   }
   if(node) {
diff --git a/src/BencodeParser.cc b/src/BencodeParser.cc
index b04f288f..84d94322 100644
--- a/src/BencodeParser.cc
+++ b/src/BencodeParser.cc
@@ -164,7 +164,7 @@ ssize_t BencodeParser::parseUpdate(const char* data, size_t size)
         i = j;
         currentState_ = BENCODE_STRING;
         if(strLength_ == 0) {
-          runCharactersCallback(0, 0);
+          runCharactersCallback(nullptr, 0);
           onStringEnd();
         }
       } else {
diff --git a/src/BitfieldMan.cc b/src/BitfieldMan.cc
index 33ea6630..4cfc9994 100644
--- a/src/BitfieldMan.cc
+++ b/src/BitfieldMan.cc
@@ -50,9 +50,9 @@ BitfieldMan::BitfieldMan(int32_t blockLength, int64_t totalLength)
    bitfieldLength_(0),
    blocks_(0),
    filterEnabled_(false),
-   bitfield_(0),
-   useBitfield_(0),
-   filterBitfield_(0),
+   bitfield_(nullptr),
+   useBitfield_(nullptr),
+   filterBitfield_(nullptr),
    cachedNumMissingBlock_(0),
    cachedNumFilteredBlock_(0),
    cachedCompletedLength_(0),
@@ -78,7 +78,7 @@ BitfieldMan::BitfieldMan(const BitfieldMan& bitfieldMan)
    filterEnabled_(bitfieldMan.filterEnabled_),
    bitfield_(new unsigned char[bitfieldLength_]),
    useBitfield_(new unsigned char[bitfieldLength_]),
-   filterBitfield_(0),
+   filterBitfield_(nullptr),
    cachedNumMissingBlock_(0),
    cachedNumFilteredBlock_(0),
    cachedCompletedLength_(0),
@@ -116,7 +116,7 @@ BitfieldMan& BitfieldMan::operator=(const BitfieldMan& bitfieldMan)
       filterBitfield_ = new unsigned char[bitfieldLength_];
       memcpy(filterBitfield_, bitfieldMan.filterBitfield_, bitfieldLength_);
     } else {
-      filterBitfield_ = 0;
+      filterBitfield_ = nullptr;
     }
 
     updateCache();
@@ -724,7 +724,7 @@ void BitfieldMan::disableFilter() {
 void BitfieldMan::clearFilter() {
   if(filterBitfield_) {
     delete [] filterBitfield_;
-    filterBitfield_ = 0;
+    filterBitfield_ = nullptr;
   }
   filterEnabled_ = false;
   updateCache();
diff --git a/src/BtBitfieldMessage.cc b/src/BtBitfieldMessage.cc
index dca8959f..a0437c91 100644
--- a/src/BtBitfieldMessage.cc
+++ b/src/BtBitfieldMessage.cc
@@ -49,14 +49,14 @@ namespace aria2 {
 const char BtBitfieldMessage::NAME[] = "bitfield";
 
 BtBitfieldMessage::BtBitfieldMessage():SimpleBtMessage(ID, NAME),
-                                       bitfield_(0),
+                                       bitfield_(nullptr),
                                        bitfieldLength_(0)
 {}
 
 BtBitfieldMessage::BtBitfieldMessage
 (const unsigned char* bitfield, size_t bitfieldLength):
   SimpleBtMessage(ID, NAME),
-  bitfield_(0),
+  bitfield_(nullptr),
   bitfieldLength_(0)
 {
   setBitfield(bitfield, bitfieldLength);
diff --git a/src/BtCheckIntegrityEntry.cc b/src/BtCheckIntegrityEntry.cc
index 79e57cd4..e88e1093 100644
--- a/src/BtCheckIntegrityEntry.cc
+++ b/src/BtCheckIntegrityEntry.cc
@@ -44,7 +44,7 @@
 namespace aria2 {
 
 BtCheckIntegrityEntry::BtCheckIntegrityEntry(RequestGroup* requestGroup):
-  PieceHashCheckIntegrityEntry(requestGroup, 0) {}
+  PieceHashCheckIntegrityEntry(requestGroup, nullptr) {}
 
 BtCheckIntegrityEntry::~BtCheckIntegrityEntry() {}
 
diff --git a/src/BtFileAllocationEntry.cc b/src/BtFileAllocationEntry.cc
index 74cc826e..4b1f4147 100644
--- a/src/BtFileAllocationEntry.cc
+++ b/src/BtFileAllocationEntry.cc
@@ -51,7 +51,7 @@
 namespace aria2 {
 
 BtFileAllocationEntry::BtFileAllocationEntry(RequestGroup* requestGroup):
-  FileAllocationEntry(requestGroup, 0) {}
+  FileAllocationEntry(requestGroup, nullptr) {}
 
 BtFileAllocationEntry::~BtFileAllocationEntry() {}
 
diff --git a/src/BtInterestedMessage.cc b/src/BtInterestedMessage.cc
index 48ce6bd7..a2fbc6b6 100644
--- a/src/BtInterestedMessage.cc
+++ b/src/BtInterestedMessage.cc
@@ -43,7 +43,7 @@ const char BtInterestedMessage::NAME[] = "interested";
 
 BtInterestedMessage::BtInterestedMessage()
   : ZeroBtMessage(ID, NAME),
-    peerStorage_(0)
+    peerStorage_(nullptr)
 {}
 
 BtInterestedMessage::~BtInterestedMessage() {}
diff --git a/src/BtNotInterestedMessage.cc b/src/BtNotInterestedMessage.cc
index e91f231c..274ec9e6 100644
--- a/src/BtNotInterestedMessage.cc
+++ b/src/BtNotInterestedMessage.cc
@@ -43,7 +43,7 @@ const char BtNotInterestedMessage::NAME[] = "not interested";
 
 BtNotInterestedMessage::BtNotInterestedMessage()
   : ZeroBtMessage(ID, NAME),
-    peerStorage_(0)
+    peerStorage_(nullptr)
 {}
 
 BtNotInterestedMessage::~BtNotInterestedMessage() {}
diff --git a/src/BtPieceMessage.cc b/src/BtPieceMessage.cc
index 2301db6d..96b092dc 100644
--- a/src/BtPieceMessage.cc
+++ b/src/BtPieceMessage.cc
@@ -72,9 +72,9 @@ BtPieceMessage::BtPieceMessage
     index_(index),
     begin_(begin),
     blockLength_(blockLength),
-    data_(0),
-    downloadContext_(0),
-    peerStorage_(0)
+    data_(nullptr),
+    downloadContext_(nullptr),
+    peerStorage_(nullptr)
 {
   setUploading(true);
 }
diff --git a/src/BtPortMessage.cc b/src/BtPortMessage.cc
index 37abc352..5e61c0eb 100644
--- a/src/BtPortMessage.cc
+++ b/src/BtPortMessage.cc
@@ -55,10 +55,10 @@ const char BtPortMessage::NAME[] = "port";
 BtPortMessage::BtPortMessage(uint16_t port)
   : SimpleBtMessage(ID, NAME),
     port_(port),
-    localNode_(0),
-    routingTable_(0),
-    taskQueue_(0),
-    taskFactory_(0)
+    localNode_(nullptr),
+    routingTable_(nullptr),
+    taskQueue_(nullptr),
+    taskFactory_(nullptr)
 {}
 
 std::unique_ptr<BtPortMessage> BtPortMessage::create
diff --git a/src/BufferedFile.cc b/src/BufferedFile.cc
index 1342c125..118cfc1b 100644
--- a/src/BufferedFile.cc
+++ b/src/BufferedFile.cc
@@ -82,7 +82,7 @@ int BufferedFile::onClose()
   int rv = 0;
   if (fp_) {
     rv = fclose(fp_);
-    fp_ = 0;
+    fp_ = nullptr;
   }
   return rv;
 }
diff --git a/src/ConsoleStatCalc.cc b/src/ConsoleStatCalc.cc
index 8fb20a96..4a29af8e 100644
--- a/src/ConsoleStatCalc.cc
+++ b/src/ConsoleStatCalc.cc
@@ -240,8 +240,8 @@ void printProgressSummary
     time_t now;
     struct tm* staticNowtmPtr;
     char buf[26];
-    if(time(&now) != (time_t)-1 && (staticNowtmPtr = localtime(&now)) != 0 &&
-       asctime_r(staticNowtmPtr, buf) != 0) {
+    if(time(&now) != (time_t)-1 && (staticNowtmPtr = localtime(&now)) != nullptr &&
+       asctime_r(staticNowtmPtr, buf) != nullptr) {
       char* lfptr = strchr(buf, '\n');
       if(lfptr) {
         *lfptr = '\0';
diff --git a/src/DHTAbstractTask.cc b/src/DHTAbstractTask.cc
index b7c100fd..2dc62297 100644
--- a/src/DHTAbstractTask.cc
+++ b/src/DHTAbstractTask.cc
@@ -47,10 +47,10 @@ namespace aria2 {
 
 DHTAbstractTask::DHTAbstractTask():
   finished_(false),
-  routingTable_(0),
-  dispatcher_(0),
-  factory_(0),
-  taskQueue_(0)
+  routingTable_(nullptr),
+  dispatcher_(nullptr),
+  factory_(nullptr),
+  taskQueue_(nullptr)
 {}
 
 bool DHTAbstractTask::finished()
diff --git a/src/DHTBucketTree.cc b/src/DHTBucketTree.cc
index 80deb65b..05a67723 100644
--- a/src/DHTBucketTree.cc
+++ b/src/DHTBucketTree.cc
@@ -45,7 +45,7 @@ namespace aria2 {
 DHTBucketTreeNode::DHTBucketTreeNode
 (DHTBucketTreeNode* left,
  DHTBucketTreeNode* right)
-  : parent_(0),
+  : parent_(nullptr),
     left_(left),
     right_(right)
 {
@@ -53,9 +53,9 @@ DHTBucketTreeNode::DHTBucketTreeNode
 }
 
 DHTBucketTreeNode::DHTBucketTreeNode(const std::shared_ptr<DHTBucket>& bucket)
-  : parent_(0),
-    left_(0),
-    right_(0),
+  : parent_(nullptr),
+    left_(nullptr),
+    right_(nullptr),
     bucket_(bucket)
 {
   memcpy(minId_, bucket_->getMinID(), DHT_ID_LENGTH);
@@ -79,7 +79,7 @@ void DHTBucketTreeNode::resetRelation()
 DHTBucketTreeNode* DHTBucketTreeNode::dig(const unsigned char* key)
 {
   if(leaf()) {
-    return 0;
+    return nullptr;
   }
   if(left_->isInRange(key)) {
     return left_;
diff --git a/src/DHTTaskFactoryImpl.cc b/src/DHTTaskFactoryImpl.cc
index 0d89164f..c11ff880 100644
--- a/src/DHTTaskFactoryImpl.cc
+++ b/src/DHTTaskFactoryImpl.cc
@@ -51,10 +51,10 @@
 namespace aria2 {
 
 DHTTaskFactoryImpl::DHTTaskFactoryImpl()
-  : routingTable_(0),
-    dispatcher_(0),
-    factory_(0),
-    taskQueue_(0),
+  : routingTable_(nullptr),
+    dispatcher_(nullptr),
+    factory_(nullptr),
+    taskQueue_(nullptr),
     timeout_(DHT_MESSAGE_TIMEOUT)
 {}
 
diff --git a/src/DHTUnknownMessage.cc b/src/DHTUnknownMessage.cc
index 46cdaf5c..025b2b33 100644
--- a/src/DHTUnknownMessage.cc
+++ b/src/DHTUnknownMessage.cc
@@ -56,7 +56,7 @@ DHTUnknownMessage::DHTUnknownMessage(const std::shared_ptr<DHTNode>& localNode,
   port_(port)
 {
   if(length_ == 0) {
-    data_ = 0;
+    data_ = nullptr;
   } else {
     data_ = new unsigned char[length];
     memcpy(data_, data, length);
diff --git a/src/DefaultBtInteractive.cc b/src/DefaultBtInteractive.cc
index 18887970..012738cd 100644
--- a/src/DefaultBtInteractive.cc
+++ b/src/DefaultBtInteractive.cc
@@ -91,7 +91,7 @@ DefaultBtInteractive::DefaultBtInteractive
     downloadContext_(downloadContext),
     peer_(peer),
     metadataGetMode_(false),
-    localNode_(0),
+    localNode_(nullptr),
     allowedFastSetSize_(10),
     haveTimer_(global::wallclock()),
     keepAliveTimer_(global::wallclock()),
@@ -104,7 +104,7 @@ DefaultBtInteractive::DefaultBtInteractive
     dhtEnabled_(false),
     numReceivedMessage_(0),
     maxOutstandingRequest_(DEFAULT_MAX_OUTSTANDING_REQUEST),
-    requestGroupMan_(0),
+    requestGroupMan_(nullptr),
     tcpPort_(0),
     haveLastSent_(global::wallclock())
 {}
diff --git a/src/DefaultBtMessageReceiver.cc b/src/DefaultBtMessageReceiver.cc
index a8d243c0..fe06d2bb 100644
--- a/src/DefaultBtMessageReceiver.cc
+++ b/src/DefaultBtMessageReceiver.cc
@@ -119,7 +119,7 @@ std::unique_ptr<BtMessage> DefaultBtMessageReceiver::receiveMessage()
 {
   size_t dataLength = 0;
   // Give 0 to PeerConnection::receiveMessage() to prevent memcpy.
-  if(!peerConnection_->receiveMessage(0, dataLength)) {
+  if(!peerConnection_->receiveMessage(nullptr, dataLength)) {
     return nullptr;
   }
   auto msg =
diff --git a/src/DefaultBtRequestFactory.cc b/src/DefaultBtRequestFactory.cc
index a7cd4838..8d62ef32 100644
--- a/src/DefaultBtRequestFactory.cc
+++ b/src/DefaultBtRequestFactory.cc
@@ -53,9 +53,9 @@
 namespace aria2 {
 
 DefaultBtRequestFactory::DefaultBtRequestFactory()
-  : pieceStorage_(0),
-    dispatcher_(0),
-    messageFactory_(0),
+  : pieceStorage_(nullptr),
+    dispatcher_(nullptr),
+    messageFactory_(nullptr),
     cuid_(0)
 {}
 
diff --git a/src/DefaultPieceStorage.cc b/src/DefaultPieceStorage.cc
index 8188d26a..7e52b0e2 100644
--- a/src/DefaultPieceStorage.cc
+++ b/src/DefaultPieceStorage.cc
@@ -84,7 +84,7 @@ DefaultPieceStorage::DefaultPieceStorage
    option_(option),
    pieceStatMan_(new PieceStatMan(downloadContext->getNumPieces(), true)),
    pieceSelector_(make_unique<RarestPieceSelector>(pieceStatMan_)),
-   wrDiskCache_(0)
+   wrDiskCache_(nullptr)
 {
   const std::string& pieceSelectorOpt =
     option_->get(PREF_STREAM_PIECE_SELECTOR);
diff --git a/src/DownloadContext.cc b/src/DownloadContext.cc
index 0dd274e1..fc5b1681 100644
--- a/src/DownloadContext.cc
+++ b/src/DownloadContext.cc
@@ -51,7 +51,7 @@ DownloadContext::DownloadContext():
   pieceLength_(0),
   checksumVerified_(false),
   knowsTotalLength_(true),
-  ownerRequestGroup_(0),
+  ownerRequestGroup_(nullptr),
   attrs_(MAX_CTX_ATTR),
   downloadStopTime_(0),
   acceptMetalink_(true) {}
@@ -62,7 +62,7 @@ DownloadContext::DownloadContext(int32_t pieceLength,
   pieceLength_(pieceLength),
   checksumVerified_(false),
   knowsTotalLength_(true),
-  ownerRequestGroup_(0),
+  ownerRequestGroup_(nullptr),
   attrs_(MAX_CTX_ATTR),
   downloadStopTime_(0),
   acceptMetalink_(true)
diff --git a/src/DownloadEngine.cc b/src/DownloadEngine.cc
index ba730076..6b200d4d 100644
--- a/src/DownloadEngine.cc
+++ b/src/DownloadEngine.cc
@@ -99,10 +99,10 @@ DownloadEngine::DownloadEngine(std::unique_ptr<EventPoll> eventPoll)
     btRegistry_(make_unique<BtRegistry>()),
 #endif // ENABLE_BITTORRENT
 #ifdef HAVE_ARES_ADDR_NODE
-    asyncDNSServers_(0),
+    asyncDNSServers_(nullptr),
 #endif // HAVE_ARES_ADDR_NODE
     dnsCache_(make_unique<DNSCache>()),
-    option_(0)
+    option_(nullptr)
 {
   unsigned char sessionId[20];
   util::generateRandomKey(sessionId);
@@ -112,7 +112,7 @@ DownloadEngine::DownloadEngine(std::unique_ptr<EventPoll> eventPoll)
 DownloadEngine::~DownloadEngine()
 {
 #ifdef HAVE_ARES_ADDR_NODE
-  setAsyncDNSServers(0);
+  setAsyncDNSServers(nullptr);
 #endif // HAVE_ARES_ADDR_NODE
 }
 
diff --git a/src/DownloadHandlerConstants.cc b/src/DownloadHandlerConstants.cc
index 0f86c6da..95b260d7 100644
--- a/src/DownloadHandlerConstants.cc
+++ b/src/DownloadHandlerConstants.cc
@@ -40,7 +40,7 @@ namespace {
 const char* METALINK_EXTENSIONS[] = {
   ".metalink", // Metalink3Spec
   ".meta4", // Metalink4Spec
-  0
+  nullptr
 };
 } // namespace
 
@@ -53,7 +53,7 @@ namespace {
 const char* METALINK_CONTENT_TYPES[] = {
   "application/metalink4+xml", // Metalink4Spec
   "application/metalink+xml", // Metalink3Spec
-  0
+  nullptr
 };
 } // namespace
 
@@ -65,7 +65,7 @@ const char** getMetalinkContentTypes()
 namespace {
 const char* BT_EXTENSIONS[] = {
   ".torrent",
-  0
+  nullptr
 };
 } // namespace
 
@@ -77,7 +77,7 @@ const char** getBtExtensions()
 namespace {
 const char* BT_CONTENT_TYPES[] = {
   "application/x-bittorrent",
-  0
+  nullptr
 };
 } // namespace
 
diff --git a/src/DownloadResult.cc b/src/DownloadResult.cc
index 6a7f35cb..49cba379 100644
--- a/src/DownloadResult.cc
+++ b/src/DownloadResult.cc
@@ -40,7 +40,7 @@
 namespace aria2 {
 
 DownloadResult::DownloadResult()
-  : gid(0),
+  : gid(nullptr),
     inMemoryDownload(false),
     sessionDownloadLength(0),
     sessionTime(0),
diff --git a/src/ExtensionMessageRegistry.cc b/src/ExtensionMessageRegistry.cc
index 8197eb1e..e821c92f 100644
--- a/src/ExtensionMessageRegistry.cc
+++ b/src/ExtensionMessageRegistry.cc
@@ -49,7 +49,7 @@ namespace {
 const char* EXTENSION_NAMES[] = {
   "ut_metadata",
   "ut_pex",
-  0
+  nullptr
 };
 } // namespace
 
@@ -63,7 +63,7 @@ const char* ExtensionMessageRegistry::getExtensionName(uint8_t id) const
 {
   int i;
   if(id == 0) {
-    return 0;
+    return nullptr;
   }
   for(i = 0; i < MAX_EXTENSION; ++i) {
     if(extensions_[i] == id) {
@@ -93,7 +93,7 @@ void ExtensionMessageRegistry::setExtensions(const Extensions& extensions)
 const char* strBtExtension(int key)
 {
   if(key >= ExtensionMessageRegistry::MAX_EXTENSION) {
-    return 0;
+    return nullptr;
   } else {
     return EXTENSION_NAMES[key];
   }
diff --git a/src/FeatureConfig.cc b/src/FeatureConfig.cc
index a61c9283..61b866f8 100644
--- a/src/FeatureConfig.cc
+++ b/src/FeatureConfig.cc
@@ -104,7 +104,7 @@ const char* strSupportedFeature(int feature)
 #ifdef ENABLE_ASYNC_DNS
     return "Async DNS";
 #else // !ENABLE_ASYNC_DNS
-    return 0;
+    return nullptr;
 #endif // !ENABLE_ASYNC_DNS
     break;
 
@@ -120,7 +120,7 @@ const char* strSupportedFeature(int feature)
 #ifdef HAVE_SQLITE3
     return "Firefox3 Cookie";
 #else // !HAVE_SQLITE3
-    return 0;
+    return nullptr;
 #endif // !HAVE_SQLITE3
     break;
 
@@ -165,7 +165,7 @@ const char* strSupportedFeature(int feature)
     break;
 
   default:
-    return 0;
+    return nullptr;
   }
 }
 
diff --git a/src/FileEntry.cc b/src/FileEntry.cc
index 478a90ac..8ea635ad 100644
--- a/src/FileEntry.cc
+++ b/src/FileEntry.cc
@@ -536,7 +536,7 @@ size_t FileEntry::setUris(const std::vector<std::string>& uris)
 bool FileEntry::addUri(const std::string& uri)
 {
   std::string peUri = util::percentEncodeMini(uri);
-  if(uri_split(NULL, peUri.c_str()) == 0) {
+  if(uri_split(nullptr, peUri.c_str()) == 0) {
     uris_.push_back(peUri);
     return true;
   } else {
@@ -547,7 +547,7 @@ bool FileEntry::addUri(const std::string& uri)
 bool FileEntry::insertUri(const std::string& uri, size_t pos)
 {
   std::string peUri = util::percentEncodeMini(uri);
-  if(uri_split(NULL, peUri.c_str()) == 0) {
+  if(uri_split(nullptr, peUri.c_str()) == 0) {
     pos = std::min(pos, uris_.size());
     uris_.insert(uris_.begin()+pos, peUri);
     return true;
diff --git a/src/GZipDecodingStreamFilter.cc b/src/GZipDecodingStreamFilter.cc
index 5939535d..ac8f5a4a 100644
--- a/src/GZipDecodingStreamFilter.cc
+++ b/src/GZipDecodingStreamFilter.cc
@@ -78,7 +78,7 @@ void GZipDecodingStreamFilter::release()
   if(strm_) {
     inflateEnd(strm_);
     delete strm_;
-    strm_ = 0;
+    strm_ = nullptr;
   }
 }
 
diff --git a/src/GZipEncoder.cc b/src/GZipEncoder.cc
index bd57c1f1..2a3f6720 100644
--- a/src/GZipEncoder.cc
+++ b/src/GZipEncoder.cc
@@ -46,7 +46,7 @@ namespace {
 const int OUTBUF_LENGTH = 4096;
 } // namespace
 
-GZipEncoder::GZipEncoder():strm_(0) {}
+GZipEncoder::GZipEncoder():strm_(nullptr) {}
 
 GZipEncoder::~GZipEncoder()
 {
@@ -74,7 +74,7 @@ void GZipEncoder::release()
   if(strm_) {
     deflateEnd(strm_);
     delete strm_;
-    strm_ = 0;
+    strm_ = nullptr;
   }
 }
 
@@ -104,7 +104,7 @@ std::string GZipEncoder::encode
 
 std::string GZipEncoder::str()
 {
-  internalBuf_ += encode(0, 0, Z_FINISH);
+  internalBuf_ += encode(nullptr, 0, Z_FINISH);
   return internalBuf_;
 }
 
diff --git a/src/GZipFile.cc b/src/GZipFile.cc
index 05350df2..a6229373 100644
--- a/src/GZipFile.cc
+++ b/src/GZipFile.cc
@@ -44,7 +44,7 @@
 namespace aria2 {
 
 GZipFile::GZipFile(const char* filename, const char* mode)
-  : fp_(0),
+  : fp_(nullptr),
     buflen_(1024), buf_(reinterpret_cast<char*>(malloc(buflen_)))
 {
   FILE* fp =
@@ -85,7 +85,7 @@ int GZipFile::onClose()
   int rv = 0;
   if (fp_) {
     rv = gzclose(fp_);
-    fp_ = 0;
+    fp_ = nullptr;
   }
   return rv;
 }
@@ -99,7 +99,7 @@ bool GZipFile::isError() const
 {
   int rv = 0;
   const char *e = gzerror(fp_, &rv);
-  return (e != 0 && *e != 0) || rv != 0;
+  return (e != nullptr && *e != 0) || rv != 0;
 }
 
 bool GZipFile::isEOF() const
diff --git a/src/GrowSegment.cc b/src/GrowSegment.cc
index c176cdde..bb5d1e54 100644
--- a/src/GrowSegment.cc
+++ b/src/GrowSegment.cc
@@ -63,7 +63,7 @@ void GrowSegment::clear(WrDiskCache* diskCache)
 {
   writtenLength_ = 0;
   // cache won't be used in this object.
-  piece_->clearAllBlock(0);
+  piece_->clearAllBlock(nullptr);
 }
 
 std::shared_ptr<Piece> GrowSegment::getPiece() const
diff --git a/src/HttpListenCommand.cc b/src/HttpListenCommand.cc
index a81929b8..1b591934 100644
--- a/src/HttpListenCommand.cc
+++ b/src/HttpListenCommand.cc
@@ -103,7 +103,7 @@ bool HttpListenCommand::bindPort(uint16_t port)
     if(e_->getOption()->getAsBool(PREF_RPC_LISTEN_ALL)) {
       flags = AI_PASSIVE;
     }
-    serverSocket_->bind(0, port, family_, flags);
+    serverSocket_->bind(nullptr, port, family_, flags);
     serverSocket_->beginListen();
     A2_LOG_INFO(fmt(MSG_LISTENING_PORT,
                     getCuid(), port));
diff --git a/src/HttpRequest.cc b/src/HttpRequest.cc
index 33469813..ea6ea973 100644
--- a/src/HttpRequest.cc
+++ b/src/HttpRequest.cc
@@ -61,9 +61,9 @@ HttpRequest::HttpRequest()
   : contentEncodingEnabled_(true),
     userAgent_(USER_AGENT),
     acceptMetalink_(false),
-    cookieStorage_(0),
-    authConfigFactory_(0),
-    option_(0),
+    cookieStorage_(nullptr),
+    authConfigFactory_(nullptr),
+    option_(nullptr),
     noCache_(true),
     acceptGzip_(false),
     endOffsetOverride_(0)
diff --git a/src/IOFile.cc b/src/IOFile.cc
index 5088f584..3cf01c69 100644
--- a/src/IOFile.cc
+++ b/src/IOFile.cc
@@ -50,7 +50,7 @@ const char IOFile::APPEND[] = "ab";
 IOFile::operator unspecified_bool_type() const
 {
   bool ok = isOpen() && !isError();
-  return ok ? &IOFile::goodState : 0;
+  return ok ? &IOFile::goodState : nullptr;
 }
 
 size_t IOFile::read(void* ptr, size_t count)
diff --git a/src/LibuvEventPoll.cc b/src/LibuvEventPoll.cc
index 321721df..43298e43 100644
--- a/src/LibuvEventPoll.cc
+++ b/src/LibuvEventPoll.cc
@@ -115,7 +115,7 @@ LibuvEventPoll::~LibuvEventPoll()
 
   if (loop_) {
     uv_loop_delete(loop_);
-    loop_ = 0;
+    loop_ = nullptr;
   }
 
   // Need this to free only after the loop is gone.
diff --git a/src/Logger.cc b/src/Logger.cc
index 6115db4e..d18bbb42 100644
--- a/src/Logger.cc
+++ b/src/Logger.cc
@@ -133,7 +133,7 @@ void writeHeader
 (Output& fp, Logger::LEVEL level, const char* sourceFile, int lineNum)
 {
   struct timeval tv;
-  gettimeofday(&tv, 0);
+  gettimeofday(&tv, nullptr);
   char datestr[20]; // 'YYYY-MM-DD hh:mm:ss'+'\0' = 20 bytes
   struct tm tm;
   //tv.tv_sec may not be of type time_t.
@@ -172,7 +172,7 @@ template<typename Output>
 void writeHeaderConsole(Output& fp, Logger::LEVEL level, bool useColor)
 {
   struct timeval tv;
-  gettimeofday(&tv, 0);
+  gettimeofday(&tv, nullptr);
   char datestr[15]; // 'MM/DD hh:mm:ss'+'\0' = 15 bytes
   struct tm tm;
   //tv.tv_sec may not be of type time_t.
diff --git a/src/MSEHandshake.cc b/src/MSEHandshake.cc
index 6cff516e..33ef8e61 100644
--- a/src/MSEHandshake.cc
+++ b/src/MSEHandshake.cc
@@ -81,12 +81,12 @@ MSEHandshake::MSEHandshake
     rbufLength_(0),
     socketBuffer_(socket),
     negotiatedCryptoType_(CRYPTO_NONE),
-    dh_(0),
+    dh_(nullptr),
     initiator_(true),
     markerIndex_(0),
     padLength_(0),
     iaLength_(0),
-    ia_(0),
+    ia_(nullptr),
     sha1_(MessageDigest::sha1())
 {}
 
diff --git a/src/MetalinkParserController.cc b/src/MetalinkParserController.cc
index 5ae75845..edf7fe09 100644
--- a/src/MetalinkParserController.cc
+++ b/src/MetalinkParserController.cc
@@ -581,7 +581,7 @@ void MetalinkParserController::setURLOfMetaurl(const std::string& url)
 #endif // ENABLE_BITTORRENT
     {
       std::string u = uri::joinUri(baseUri_, url);
-      if(uri_split(NULL, u.c_str()) == 0) {
+      if(uri_split(nullptr, u.c_str()) == 0) {
         tMetaurl_->url = u;
       } else {
         tMetaurl_->url = url;
diff --git a/src/MetalinkParserStateImpl.cc b/src/MetalinkParserStateImpl.cc
index bcc76029..0692d7f9 100644
--- a/src/MetalinkParserStateImpl.cc
+++ b/src/MetalinkParserStateImpl.cc
@@ -58,7 +58,7 @@ public:
   bool operator()(const XmlAttr& attr) const
   {
     return strcmp(attr.localname, localname_) == 0 &&
-      (attr.nsUri == 0 || strcmp(attr.nsUri, nsUri_) == 0);
+      (attr.nsUri == nullptr || strcmp(attr.nsUri, nsUri_) == 0);
   }
 };
 } // namespace
diff --git a/src/NameResolver.cc b/src/NameResolver.cc
index 33954423..ddb9979e 100644
--- a/src/NameResolver.cc
+++ b/src/NameResolver.cc
@@ -52,7 +52,7 @@ void NameResolver::resolve(std::vector<std::string>& resolvedAddresses,
 {
   struct addrinfo* res;
   int s;
-  s = callGetaddrinfo(&res, hostname.c_str(), 0, family_, socktype_, 0, 0);
+  s = callGetaddrinfo(&res, hostname.c_str(), nullptr, family_, socktype_, 0, 0);
   if(s) {
     throw DL_ABORT_EX2(fmt(EX_RESOLVE_HOSTNAME,
                            hostname.c_str(), gai_strerror(s)),
diff --git a/src/Option.cc b/src/Option.cc
index 00ada34a..72bc52be 100644
--- a/src/Option.cc
+++ b/src/Option.cc
@@ -122,7 +122,7 @@ int32_t Option::getAsInt(const Pref* pref) const {
   if(value.empty()) {
     return 0;
   } else {
-    return strtol(value.c_str(), 0, 10);
+    return strtol(value.c_str(), nullptr, 10);
   }
 }
 
@@ -131,7 +131,7 @@ int64_t Option::getAsLLInt(const Pref* pref) const {
   if(value.empty()) {
     return 0;
   } else {
-    return strtoll(value.c_str(), 0, 10);
+    return strtoll(value.c_str(), nullptr, 10);
   }
 }
 
@@ -144,7 +144,7 @@ double Option::getAsDouble(const Pref* pref) const {
   if(value.empty()) {
     return 0.0;
   } else {
-    return strtod(value.c_str(), 0);
+    return strtod(value.c_str(), nullptr);
   }
 }
 
diff --git a/src/OptionHandlerImpl.cc b/src/OptionHandlerImpl.cc
index 3e8fc8a0..75a40354 100644
--- a/src/OptionHandlerImpl.cc
+++ b/src/OptionHandlerImpl.cc
@@ -241,7 +241,7 @@ FloatNumberOptionHandler::~FloatNumberOptionHandler() {}
 void FloatNumberOptionHandler::parseArg
 (Option& option, const std::string& optarg) const
 {
-  double number = strtod(optarg.c_str(), 0);
+  double number = strtod(optarg.c_str(), nullptr);
   if((min_ < 0 || min_ <= number) && (max_ < 0 || number <= max_)) {
     option.put(pref_, optarg);
   } else {
diff --git a/src/OptionHandlerImpl.h b/src/OptionHandlerImpl.h
index 05d66fd2..a1e963db 100644
--- a/src/OptionHandlerImpl.h
+++ b/src/OptionHandlerImpl.h
@@ -271,7 +271,7 @@ public:
   // argument.
   DeprecatedOptionHandler
   (OptionHandler* depOptHandler,
-   const OptionHandler* repOptHandler = 0);
+   const OptionHandler* repOptHandler = nullptr);
   virtual ~DeprecatedOptionHandler();
   virtual void parse(Option& option, const std::string& arg) const
     CXX11_OVERRIDE;
diff --git a/src/OptionParser.cc b/src/OptionParser.cc
index bcb900cb..154045dc 100644
--- a/src/OptionParser.cc
+++ b/src/OptionParser.cc
@@ -59,7 +59,7 @@
 namespace aria2 {
 
 OptionParser::OptionParser()
-  : handlers_(option::countOption(), 0),
+  : handlers_(option::countOption(), nullptr),
     shortOpts_(256)
 {}
 
@@ -111,15 +111,15 @@ void putOptions(struct option* longOpts, int* plopt,
         (*longOpts).flag = plopt;
         (*longOpts).val = (*first)->getPref()->i;
       } else {
-        (*longOpts).flag = 0;
+        (*longOpts).flag = nullptr;
         (*longOpts).val = (*first)->getShortName();
       }
       ++longOpts;
     }
   }
-  (*longOpts).name = 0;
+  (*longOpts).name = nullptr;
   (*longOpts).has_arg = 0;
-  (*longOpts).flag = 0;
+  (*longOpts).flag = nullptr;
   (*longOpts).val = 0;
 }
 } // namespace
@@ -156,11 +156,11 @@ void OptionParser::parseArg
   putOptions(longOpts.get(), &lopt, handlers_.begin(), handlers_.end());
   std::string optstring = createOptstring(handlers_.begin(), handlers_.end());
   while(1) {
-    int c = getopt_long(argc, argv, optstring.c_str(), longOpts.get(), 0);
+    int c = getopt_long(argc, argv, optstring.c_str(), longOpts.get(), nullptr);
     if(c == -1) {
       break;
     }
-    const OptionHandler* op = 0;
+    const OptionHandler* op = nullptr;
     if(c == 0) {
       op = findById(lopt);
     } else if(c != '?') {
diff --git a/src/Peer.cc b/src/Peer.cc
index 4edcebb9..06e08b8e 100644
--- a/src/Peer.cc
+++ b/src/Peer.cc
@@ -53,7 +53,7 @@ Peer::Peer(std::string ipaddr, uint16_t port, bool incoming):
   firstContactTime_(global::wallclock()),
   dropStartTime_(0),
   seeder_(false),
-  res_(0),
+  res_(nullptr),
   incoming_(incoming),
   localPeer_(false),
   disconnectedGracefully_(false)
@@ -88,7 +88,7 @@ void Peer::reconfigureSessionResource(int32_t pieceLength, int64_t totalLength)
 void Peer::releaseSessionResource()
 {
   delete res_;
-  res_ = 0;
+  res_ = nullptr;
 }
 
 void Peer::setPeerId(const unsigned char* peerId)
diff --git a/src/Peer.h b/src/Peer.h
index b0f4a09e..e146580c 100644
--- a/src/Peer.h
+++ b/src/Peer.h
@@ -129,7 +129,7 @@ public:
   // Returns true iff res_ != 0.
   bool isActive() const
   {
-    return res_ != 0;
+    return res_ != nullptr;
   }
 
   void setPeerId(const unsigned char* peerId);
diff --git a/src/PeerListenCommand.cc b/src/PeerListenCommand.cc
index a7e3a147..4c137e55 100644
--- a/src/PeerListenCommand.cc
+++ b/src/PeerListenCommand.cc
@@ -77,7 +77,7 @@ bool PeerListenCommand::bindPort(uint16_t& port, SegList<int>& sgl)
         eoi = ports.end(); i != eoi; ++i) {
     port = *i;
     try {
-      socket_->bind(0, port, family_);
+      socket_->bind(nullptr, port, family_);
       socket_->beginListen();
       A2_LOG_NOTICE(fmt(_("IPv%d BitTorrent: listening on TCP port %u"),
                         ipv, port));
diff --git a/src/PeerReceiveHandshakeCommand.cc b/src/PeerReceiveHandshakeCommand.cc
index 981fec37..e9ed7fb7 100644
--- a/src/PeerReceiveHandshakeCommand.cc
+++ b/src/PeerReceiveHandshakeCommand.cc
@@ -96,7 +96,7 @@ bool PeerReceiveHandshakeCommand::executeInternal()
     size_t dataLength = 0;
     // Ignore return value. The received data is kept in
     // PeerConnection object because of peek = true.
-    peerConnection_->receiveHandshake(0, dataLength, true);
+    peerConnection_->receiveHandshake(nullptr, dataLength, true);
   }
   if(peerConnection_->getBufferLength() >= 48) {
     const unsigned char* data = peerConnection_->getBuffer();
diff --git a/src/PeerSessionResource.cc b/src/PeerSessionResource.cc
index 2bb779d4..becf1f03 100644
--- a/src/PeerSessionResource.cc
+++ b/src/PeerSessionResource.cc
@@ -49,7 +49,7 @@ PeerSessionResource::PeerSessionResource(int32_t pieceLength, int64_t totalLengt
   bitfieldMan_(new BitfieldMan(pieceLength, totalLength)),
   lastDownloadUpdate_(0),
   lastAmUnchoking_(0),
-  dispatcher_(0),
+  dispatcher_(nullptr),
   amChoking_(true),
   amInterested_(false),
   peerChoking_(true),
diff --git a/src/Piece.cc b/src/Piece.cc
index 24e5beff..4c779626 100644
--- a/src/Piece.cc
+++ b/src/Piece.cc
@@ -52,8 +52,8 @@
 
 namespace aria2 {
 
-Piece::Piece():index_(0), length_(0), blockLength_(BLOCK_LENGTH), bitfield_(0),
-               usedBySegment_(false), wrCache_(0)
+Piece::Piece():index_(0), length_(0), blockLength_(BLOCK_LENGTH), bitfield_(nullptr),
+               usedBySegment_(false), wrCache_(nullptr)
 #ifdef ENABLE_MESSAGE_DIGEST
               , nextBegin_(0)
 #endif // ENABLE_MESSAGE_DIGEST
@@ -64,7 +64,7 @@ Piece::Piece(size_t index, int32_t length, int32_t blockLength)
    length_(length),
    blockLength_(blockLength),
    bitfield_(new BitfieldMan(blockLength_, length)),
-   usedBySegment_(false), wrCache_(0)
+   usedBySegment_(false), wrCache_(nullptr)
 #ifdef ENABLE_MESSAGE_DIGEST
  ,nextBegin_(0)
 #endif // ENABLE_MESSAGE_DIGEST
@@ -325,7 +325,7 @@ void Piece::initWrCache(WrDiskCache* diskCache,
   if(!diskCache) {
     return;
   }
-  assert(wrCache_ == 0);
+  assert(wrCache_ == nullptr);
   wrCache_ = new WrDiskCacheEntry(diskAdaptor);
   bool rv = diskCache->add(wrCache_);
   assert(rv);
@@ -396,7 +396,7 @@ void Piece::releaseWrCache(WrDiskCache* diskCache)
   if(diskCache && wrCache_) {
     diskCache->remove(wrCache_);
     delete wrCache_;
-    wrCache_ = 0;
+    wrCache_ = nullptr;
   }
 }
 
diff --git a/src/ProtocolDetector.cc b/src/ProtocolDetector.cc
index 4326e77d..be914e14 100644
--- a/src/ProtocolDetector.cc
+++ b/src/ProtocolDetector.cc
@@ -55,7 +55,7 @@ ProtocolDetector::~ProtocolDetector() {}
 
 bool ProtocolDetector::isStreamProtocol(const std::string& uri) const
 {
-  return uri_split(NULL, uri.c_str()) == 0;
+  return uri_split(nullptr, uri.c_str()) == 0;
 }
 
 bool ProtocolDetector::guessTorrentFile(const std::string& uri) const
diff --git a/src/RequestGroup.cc b/src/RequestGroup.cc
index aef696ec..93c466df 100644
--- a/src/RequestGroup.cc
+++ b/src/RequestGroup.cc
@@ -141,15 +141,15 @@ RequestGroup::RequestGroup(const std::shared_ptr<GroupId>& gid,
     fileNotFoundCount_(0),
     timeout_(option->getAsInt(PREF_TIMEOUT)),
 #ifdef ENABLE_BITTORRENT
-    btRuntime_(0),
-    peerStorage_(0),
+    btRuntime_(nullptr),
+    peerStorage_(nullptr),
 #endif // ENABLE_BITTORRENT
     inMemoryDownload_(false),
     maxDownloadSpeedLimit_(option->getAsInt(PREF_MAX_DOWNLOAD_LIMIT)),
     maxUploadSpeedLimit_(option->getAsInt(PREF_MAX_UPLOAD_LIMIT)),
     lastErrorCode_(error_code::UNDEFINED),
     belongsToGID_(0),
-    requestGroupMan_(0),
+    requestGroupMan_(nullptr),
     resumeFailureCount_(0)
 {
   fileAllocationEnabled_ = option_->get(PREF_FILE_ALLOCATION) != V_NONE;
@@ -314,7 +314,7 @@ void RequestGroup::createInitialCommand
         }
       }
 
-      DefaultBtProgressInfoFile* progressInfoFilePtr = 0;
+      DefaultBtProgressInfoFile* progressInfoFilePtr = nullptr;
       std::shared_ptr<BtProgressInfoFile> progressInfoFile;
       if(!metadataGetMode) {
         progressInfoFilePtr = new DefaultBtProgressInfoFile(downloadContext_,
@@ -997,8 +997,8 @@ void RequestGroup::releaseRuntimeResource(DownloadEngine* e)
 {
 #ifdef ENABLE_BITTORRENT
   e->getBtRegistry()->remove(gid_->getNumericId());
-  btRuntime_ = 0;
-  peerStorage_ = 0;
+  btRuntime_ = nullptr;
+  peerStorage_ = nullptr;
 #endif // ENABLE_BITTORRENT
   if(pieceStorage_) {
     pieceStorage_->removeAdvertisedPiece(0);
diff --git a/src/RequestGroupMan.cc b/src/RequestGroupMan.cc
index e3a461eb..d446280b 100644
--- a/src/RequestGroupMan.cc
+++ b/src/RequestGroupMan.cc
@@ -111,7 +111,7 @@ RequestGroupMan::RequestGroupMan
     removedErrorResult_(0),
     removedLastErrorResult_(error_code::FINISHED),
     maxDownloadResult_(option->getAsInt(PREF_MAX_DOWNLOAD_RESULT)),
-    wrDiskCache_(0)
+    wrDiskCache_(nullptr)
 {
   appendReservedGroup(reservedGroups_,
                       requestGroups.begin(), requestGroups.end());
@@ -962,7 +962,7 @@ void RequestGroupMan::setUriListParser
 
 void RequestGroupMan::initWrDiskCache()
 {
-  assert(wrDiskCache_ == 0);
+  assert(wrDiskCache_ == nullptr);
   size_t limit = option_->getAsInt(PREF_DISK_CACHE);
   if(limit > 0) {
     wrDiskCache_ = new WrDiskCache(limit);
diff --git a/src/SelectEventPoll.cc b/src/SelectEventPoll.cc
index 11a6c156..7974f3ba 100644
--- a/src/SelectEventPoll.cc
+++ b/src/SelectEventPoll.cc
@@ -198,7 +198,7 @@ void SelectEventPoll::poll(const struct timeval& tv)
 #ifdef __MINGW32__
     retval = select(fdmax_+1, &rfds, &wfds, &efds, &ttv);
 #else // !__MINGW32__
-    retval = select(fdmax_+1, &rfds, &wfds, NULL, &ttv);
+    retval = select(fdmax_+1, &rfds, &wfds, nullptr, &ttv);
 #endif // !__MINGW32__
   } while(retval == -1 && errno == EINTR);
   if(retval > 0) {
diff --git a/src/SimpleRandomizer.cc b/src/SimpleRandomizer.cc
index 5d304243..aaba91a4 100644
--- a/src/SimpleRandomizer.cc
+++ b/src/SimpleRandomizer.cc
@@ -56,7 +56,7 @@ const std::unique_ptr<SimpleRandomizer>& SimpleRandomizer::getInstance()
 void SimpleRandomizer::init()
 {
 #ifndef __MINGW32__
-  srandom(time(0)^getpid());
+  srandom(time(nullptr)^getpid());
 #endif // !__MINGW32__
 }
 
diff --git a/src/SingleFileAllocationIterator.cc b/src/SingleFileAllocationIterator.cc
index 2e97b124..be31d820 100644
--- a/src/SingleFileAllocationIterator.cc
+++ b/src/SingleFileAllocationIterator.cc
@@ -55,7 +55,7 @@ SingleFileAllocationIterator::SingleFileAllocationIterator
   : stream_(stream),
     offset_(offset),
     totalLength_(totalLength),
-    buffer_(0)
+    buffer_(nullptr)
 {}
 
 SingleFileAllocationIterator::~SingleFileAllocationIterator()
diff --git a/src/SinkStreamFilter.h b/src/SinkStreamFilter.h
index ebb72c1a..debfa409 100644
--- a/src/SinkStreamFilter.h
+++ b/src/SinkStreamFilter.h
@@ -47,7 +47,7 @@ private:
   bool hashUpdate_;
   size_t bytesProcessed_;
 public:
-  SinkStreamFilter(WrDiskCache* wrDiskCache = 0, bool hashUpdate = false);
+  SinkStreamFilter(WrDiskCache* wrDiskCache = nullptr, bool hashUpdate = false);
 
   virtual void init() CXX11_OVERRIDE {}
 
diff --git a/src/SocketCore.cc b/src/SocketCore.cc
index ca451339..6cfc3b75 100644
--- a/src/SocketCore.cc
+++ b/src/SocketCore.cc
@@ -103,12 +103,12 @@ std::string errorMsg(int errNum)
   if (FormatMessage(
                     FORMAT_MESSAGE_FROM_SYSTEM |
                     FORMAT_MESSAGE_IGNORE_INSERTS,
-                    NULL,
+                    nullptr,
                     errNum,
                     MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
                     (LPTSTR) &buf,
                     sizeof(buf),
-                    NULL
+                    nullptr
                     ) == 0) {
     snprintf(buf, sizeof(buf), EX_SOCKET_UNKNOWN_ERROR, errNum, errNum);
   }
@@ -267,7 +267,7 @@ void SocketCore::bindWithFamily(uint16_t port, int family, int flags)
 {
   closeConnection();
   std::string error;
-  sock_t fd = bindTo(0, port, family, sockType_, flags, error);
+  sock_t fd = bindTo(nullptr, port, family, sockType_, flags, error);
   if(fd == (sock_t) -1) {
     throw DL_ABORT_EX(fmt(EX_SOCKET_BIND, error.c_str()));
   } else {
@@ -284,7 +284,7 @@ void SocketCore::bind
   if(addr && addr[0]) {
     addrp = addr;
   } else {
-    addrp = 0;
+    addrp = nullptr;
   }
   if(!(flags&AI_PASSIVE) || bindAddrs_.empty()) {
     sock_t fd = bindTo(addrp, port, family, sockType_, flags, error);
@@ -297,7 +297,7 @@ void SocketCore::bind
         i != eoi; ++i) {
       char host[NI_MAXHOST];
       int s;
-      s = getnameinfo(&(*i).first.sa, (*i).second, host, NI_MAXHOST, 0, 0,
+      s = getnameinfo(&(*i).first.sa, (*i).second, host, NI_MAXHOST, nullptr, 0,
                       NI_NUMERICHOST);
       if(s) {
         error = gai_strerror(s);
@@ -321,7 +321,7 @@ void SocketCore::bind
 
 void SocketCore::bind(uint16_t port, int flags)
 {
-  bind(0, port, protocolFamily_, flags);
+  bind(nullptr, port, protocolFamily_, flags);
 }
 
 void SocketCore::bind(const struct sockaddr* addr, socklen_t addrlen)
@@ -622,7 +622,7 @@ bool SocketCore::isWritable(time_t timeout)
   tv.tv_sec = timeout;
   tv.tv_usec = 0;
 
-  int r = select(sockfd_+1, NULL, &fds, NULL, &tv);
+  int r = select(sockfd_+1, nullptr, &fds, nullptr, &tv);
   int errNum = SOCKET_ERRNO;
   if(r == 1) {
     return true;
@@ -668,7 +668,7 @@ bool SocketCore::isReadable(time_t timeout)
   tv.tv_sec = timeout;
   tv.tv_usec = 0;
 
-  int r = select(sockfd_+1, &fds, NULL, NULL, &tv);
+  int r = select(sockfd_+1, &fds, nullptr, nullptr, &tv);
   int errNum = SOCKET_ERRNO;
   if(r == 1) {
     return true;
@@ -986,7 +986,7 @@ void SocketCore::bindAddress(const std::string& iface)
         i != eoi; ++i) {
       char host[NI_MAXHOST];
       int s;
-      s = getnameinfo(&(*i).first.sa, (*i).second, host, NI_MAXHOST, 0, 0,
+      s = getnameinfo(&(*i).first.sa, (*i).second, host, NI_MAXHOST, nullptr, 0,
                       NI_NUMERICHOST);
       if(s == 0) {
         A2_LOG_DEBUG(fmt("Sockets will bind to %s", host));
@@ -1002,7 +1002,7 @@ void getInterfaceAddress
   A2_LOG_DEBUG(fmt("Finding interface %s", iface.c_str()));
 #ifdef HAVE_GETIFADDRS
   // First find interface in interface addresses
-  struct ifaddrs* ifaddr = 0;
+  struct ifaddrs* ifaddr = nullptr;
   if(getifaddrs(&ifaddr) == -1) {
     int errNum = SOCKET_ERRNO;
     A2_LOG_INFO(fmt(MSG_INTERFACE_NOT_FOUND,
@@ -1044,7 +1044,7 @@ void getInterfaceAddress
   if(ifAddrs.empty()) {
     addrinfo* res;
     int s;
-    s = callGetaddrinfo(&res, iface.c_str(), 0, family, SOCK_STREAM, aiFlags,0);
+    s = callGetaddrinfo(&res, iface.c_str(), nullptr, family, SOCK_STREAM, aiFlags,0);
     if(s) {
       A2_LOG_INFO(fmt(MSG_INTERFACE_NOT_FOUND, iface.c_str(), gai_strerror(s)));
     } else {
@@ -1111,7 +1111,7 @@ int inetNtop(int af, const void* src, char* dst, socklen_t size)
 #endif // HAVE_SOCKADDR_IN_SIN_LEN
     memcpy(&su.in.sin_addr, src, sizeof(su.in.sin_addr));
     s = getnameinfo(&su.sa, sizeof(su.in),
-                    dst, size, 0, 0, NI_NUMERICHOST);
+                    dst, size, nullptr, 0, NI_NUMERICHOST);
   } else if(af == AF_INET6) {
     su.in6.sin6_family = AF_INET6;
 #ifdef HAVE_SOCKADDR_IN6_SIN6_LEN
@@ -1119,7 +1119,7 @@ int inetNtop(int af, const void* src, char* dst, socklen_t size)
 #endif // HAVE_SOCKADDR_IN6_SIN6_LEN
     memcpy(&su.in6.sin6_addr, src, sizeof(su.in6.sin6_addr));
     s = getnameinfo(&su.sa, sizeof(su.in6),
-                    dst, size, 0, 0, NI_NUMERICHOST);
+                    dst, size, nullptr, 0, NI_NUMERICHOST);
   } else {
     s = EAI_FAMILY;
   }
@@ -1157,7 +1157,7 @@ size_t getBinAddr(void* dest, const std::string& ip)
 {
   size_t len = 0;
   addrinfo* res;
-  if(callGetaddrinfo(&res, ip.c_str(), 0, AF_UNSPEC,
+  if(callGetaddrinfo(&res, ip.c_str(), nullptr, AF_UNSPEC,
                      0, AI_NUMERICHOST, 0) != 0) {
     return len;
   }
@@ -1307,7 +1307,7 @@ void checkAddrconfig()
   A2_LOG_INFO("Checking configured addresses");
   ipv4AddrConfigured = false;
   ipv6AddrConfigured = false;
-  ifaddrs* ifaddr = 0;
+  ifaddrs* ifaddr = nullptr;
   int rv;
   rv = getifaddrs(&ifaddr);
   if(rv == -1) {
@@ -1348,7 +1348,7 @@ void checkAddrconfig()
     default:
       continue;
     }
-    rv = getnameinfo(ifa->ifa_addr, addrlen, host, NI_MAXHOST, 0, 0,
+    rv = getnameinfo(ifa->ifa_addr, addrlen, host, NI_MAXHOST, nullptr, 0,
                      NI_NUMERICHOST);
     if(rv == 0) {
       if(found) {
diff --git a/src/TimeA2.cc b/src/TimeA2.cc
index 836b7e58..89ec0278 100644
--- a/src/TimeA2.cc
+++ b/src/TimeA2.cc
@@ -80,12 +80,12 @@ bool Time::operator<(const Time& time) const
 }
 
 void Time::reset() {
-  gettimeofday(&tv_, 0);
+  gettimeofday(&tv_, nullptr);
 }
 
 struct timeval Time::getCurrentTime() const {
   struct timeval now;
-  gettimeofday(&now, 0);
+  gettimeofday(&now, nullptr);
   return now;
 }
 
@@ -94,7 +94,7 @@ bool Time::elapsed(time_t sec) const {
   // the time this function is called before specified time passes, we first do
   // simple test using time.
   // Then only when the further test is required, call gettimeofday.
-  time_t now = time(0);
+  time_t now = time(nullptr);
   if(tv_.tv_sec+sec < now) {
     return true;
   } else if(tv_.tv_sec+sec == now) {
diff --git a/src/TimerA2.cc b/src/TimerA2.cc
index 3ed6b564..29e5d32f 100644
--- a/src/TimerA2.cc
+++ b/src/TimerA2.cc
@@ -95,7 +95,7 @@ static timeval getCurrentTime()
     tv.tv_sec = ts.tv_sec+2678400; // 1month offset(24*3600*31)
     tv.tv_usec = ts.tv_nsec/1000;
   } else {
-    gettimeofday(&tv, 0);
+    gettimeofday(&tv, nullptr);
   }
   return tv;
 }
diff --git a/src/UDPTrackerClient.cc b/src/UDPTrackerClient.cc
index 024776f8..23192e04 100644
--- a/src/UDPTrackerClient.cc
+++ b/src/UDPTrackerClient.cc
@@ -474,12 +474,12 @@ UDPTrackerConnection* UDPTrackerClient::getConnectionId
            UDPTrackerConnection>::iterator i =
     connectionIdCache_.find(std::make_pair(remoteAddr, remotePort));
   if(i == connectionIdCache_.end()) {
-    return 0;
+    return nullptr;
   }
   if((*i).second.state == UDPT_CST_CONNECTED &&
      (*i).second.lastUpdated.difference(now) > 60) {
     connectionIdCache_.erase(i);
-    return 0;
+    return nullptr;
   } else {
     return &(*i).second;
   }
diff --git a/src/UnknownLengthPieceStorage.cc b/src/UnknownLengthPieceStorage.cc
index dcacccb2..8813e9bb 100644
--- a/src/UnknownLengthPieceStorage.cc
+++ b/src/UnknownLengthPieceStorage.cc
@@ -156,7 +156,7 @@ std::shared_ptr<Piece> UnknownLengthPieceStorage::getMissingPiece
  cuid_t cuid)
 {
   if(index == 0) {
-    return getMissingPiece(0, 0, 0, cuid);
+    return getMissingPiece(0, nullptr, 0, cuid);
   } else {
     return nullptr;
   }
diff --git a/src/UnknownLengthPieceStorage.h b/src/UnknownLengthPieceStorage.h
index f74adf03..5aad9667 100644
--- a/src/UnknownLengthPieceStorage.h
+++ b/src/UnknownLengthPieceStorage.h
@@ -205,7 +205,7 @@ public:
 
   virtual const unsigned char* getBitfield() CXX11_OVERRIDE
   {
-    return 0;
+    return nullptr;
   }
 
   virtual void setBitfield(const unsigned char* bitfield,
@@ -232,7 +232,7 @@ public:
 
   virtual std::shared_ptr<DiskAdaptor> getDiskAdaptor() CXX11_OVERRIDE;
 
-  virtual WrDiskCache* getWrDiskCache() CXX11_OVERRIDE { return 0; }
+  virtual WrDiskCache* getWrDiskCache() CXX11_OVERRIDE { return nullptr; }
 
   virtual void flushWrDiskCacheEntry() CXX11_OVERRIDE {}
 
diff --git a/src/WatchProcessCommand.cc b/src/WatchProcessCommand.cc
index 6ad2b8f7..0efee39e 100644
--- a/src/WatchProcessCommand.cc
+++ b/src/WatchProcessCommand.cc
@@ -107,7 +107,7 @@ void WatchProcessCommand::process()
   mib[2]=KERN_PROC_PID;
   mib[3]=pid_;
 
-  int ret = sysctl(mib, MIBSIZE, &kp, &len, NULL, 0);
+  int ret = sysctl(mib, MIBSIZE, &kp, &len, nullptr, 0);
   if (ret == -1 || len <= 0) {
     waiting = false;
   }
diff --git a/src/WebSocketSession.cc b/src/WebSocketSession.cc
index 2e3d28a2..86fb08d2 100644
--- a/src/WebSocketSession.cc
+++ b/src/WebSocketSession.cc
@@ -160,7 +160,7 @@ void onMsgRecvCallback(wslay_event_context_ptr wsctx,
   if(!wslay_is_ctrl_frame(arg->opcode)) {
     // TODO Only process text frame
     ssize_t error = 0;
-    auto json = wsSession->parseFinal(0, 0, error);
+    auto json = wsSession->parseFinal(nullptr, 0, error);
     if(error < 0) {
       A2_LOG_INFO("Failed to parse JSON-RPC request");
       RpcResponse res
diff --git a/src/Xml2XmlParser.cc b/src/Xml2XmlParser.cc
index f7499733..bcc87827 100644
--- a/src/Xml2XmlParser.cc
+++ b/src/Xml2XmlParser.cc
@@ -121,45 +121,45 @@ void mlCharacters(void* userData, const xmlChar* ch, int len)
 namespace {
 xmlSAXHandler mySAXHandler =
   {
-    0, // internalSubsetSAXFunc
-    0, // isStandaloneSAXFunc
-    0, // hasInternalSubsetSAXFunc
-    0, // hasExternalSubsetSAXFunc
-    0, // resolveEntitySAXFunc
-    0, // getEntitySAXFunc
-    0, // entityDeclSAXFunc
-    0, // notationDeclSAXFunc
-    0, // attributeDeclSAXFunc
-    0, // elementDeclSAXFunc
-    0, //   unparsedEntityDeclSAXFunc
-    0, //   setDocumentLocatorSAXFunc
-    0, //   startDocumentSAXFunc
-    0, //   endDocumentSAXFunc
-    0, //   startElementSAXFunc
-    0, //   endElementSAXFunc
-    0, //   referenceSAXFunc
+    nullptr, // internalSubsetSAXFunc
+    nullptr, // isStandaloneSAXFunc
+    nullptr, // hasInternalSubsetSAXFunc
+    nullptr, // hasExternalSubsetSAXFunc
+    nullptr, // resolveEntitySAXFunc
+    nullptr, // getEntitySAXFunc
+    nullptr, // entityDeclSAXFunc
+    nullptr, // notationDeclSAXFunc
+    nullptr, // attributeDeclSAXFunc
+    nullptr, // elementDeclSAXFunc
+    nullptr, //   unparsedEntityDeclSAXFunc
+    nullptr, //   setDocumentLocatorSAXFunc
+    nullptr, //   startDocumentSAXFunc
+    nullptr, //   endDocumentSAXFunc
+    nullptr, //   startElementSAXFunc
+    nullptr, //   endElementSAXFunc
+    nullptr, //   referenceSAXFunc
     &mlCharacters, //   charactersSAXFunc
-    0, //   ignorableWhitespaceSAXFunc
-    0, //   processingInstructionSAXFunc
-    0, //   commentSAXFunc
-    0, //   warningSAXFunc
-    0, //   errorSAXFunc
-    0, //   fatalErrorSAXFunc
-    0, //   getParameterEntitySAXFunc
-    0, //   cdataBlockSAXFunc
-    0, //   externalSubsetSAXFunc
+    nullptr, //   ignorableWhitespaceSAXFunc
+    nullptr, //   processingInstructionSAXFunc
+    nullptr, //   commentSAXFunc
+    nullptr, //   warningSAXFunc
+    nullptr, //   errorSAXFunc
+    nullptr, //   fatalErrorSAXFunc
+    nullptr, //   getParameterEntitySAXFunc
+    nullptr, //   cdataBlockSAXFunc
+    nullptr, //   externalSubsetSAXFunc
     XML_SAX2_MAGIC, //   unsigned int        initialized
-    0, //   void *      _private
+    nullptr, //   void *      _private
     &mlStartElement, //   startElementNsSAX2Func
     &mlEndElement, //   endElementNsSAX2Func
-    0, //   xmlStructuredErrorFunc
+    nullptr, //   xmlStructuredErrorFunc
   };
 } // namespace
 
 XmlParser::XmlParser(ParserStateMachine* psm)
   : psm_(psm),
     sessionData_(psm),
-    ctx_(xmlCreatePushParserCtxt(&mySAXHandler, &sessionData_, 0, 0, 0)),
+    ctx_(xmlCreatePushParserCtxt(&mySAXHandler, &sessionData_, nullptr, 0, nullptr)),
     lastError_(0)
 {}
 
@@ -198,7 +198,7 @@ int XmlParser::reset()
 {
   psm_->reset();
   sessionData_.reset();
-  int rv = xmlCtxtResetPush(ctx_, 0, 0, 0, 0);
+  int rv = xmlCtxtResetPush(ctx_, nullptr, 0, nullptr, nullptr);
   if(rv != 0) {
     return lastError_ = ERR_RESET;
   } else {
diff --git a/src/XmlAttr.cc b/src/XmlAttr.cc
index 404ebd1e..9baf66ec 100644
--- a/src/XmlAttr.cc
+++ b/src/XmlAttr.cc
@@ -37,10 +37,10 @@
 namespace aria2 {
 
 XmlAttr::XmlAttr()
-  : localname(0),
-    prefix(0),
-    nsUri(0),
-    value(0),
+  : localname(nullptr),
+    prefix(nullptr),
+    nsUri(nullptr),
+    value(nullptr),
     valueLength(0)
 {}
 
diff --git a/src/XmlParser.cc b/src/XmlParser.cc
index 1a0ad331..bf46592c 100644
--- a/src/XmlParser.cc
+++ b/src/XmlParser.cc
@@ -65,7 +65,7 @@ bool parseFile(const std::string& filename, ParserStateMachine* psm)
     }
   }
   if(nread == 0 && retval) {
-    if(ps.parseFinal(0, 0) < 0) {
+    if(ps.parseFinal(nullptr, 0) < 0) {
       retval = false;
     }
   }
diff --git a/src/XmlRpcDiskWriter.cc b/src/XmlRpcDiskWriter.cc
index bfa8a92c..8d610a04 100644
--- a/src/XmlRpcDiskWriter.cc
+++ b/src/XmlRpcDiskWriter.cc
@@ -62,7 +62,7 @@ void XmlRpcDiskWriter::writeData(const unsigned char* data, size_t len,
 
 int XmlRpcDiskWriter::finalize()
 {
-  return parser_.parseFinal(0, 0);
+  return parser_.parseFinal(nullptr, 0);
 }
 
 RpcRequest XmlRpcDiskWriter::getResult()
diff --git a/src/aria2api.cc b/src/aria2api.cc
index 32ae2046..8196744f 100644
--- a/src/aria2api.cc
+++ b/src/aria2api.cc
@@ -69,7 +69,7 @@
 namespace aria2 {
 
 Session::Session(const KeyVals& options)
-  : context(new Context(false, 0, 0, options))
+  : context(new Context(false, 0, nullptr, options))
 {}
 
 Session::~Session()
@@ -78,12 +78,12 @@ Session::~Session()
 SessionConfig::SessionConfig()
   : keepRunning(false),
     useSignalHandler(true),
-    downloadEventCallback(0),
-    userData(0)
+    downloadEventCallback(nullptr),
+    userData(nullptr)
 {}
 
 namespace {
-Platform* platform = 0;
+Platform* platform = nullptr;
 } // namespace
 
 int libraryInit()
@@ -934,7 +934,7 @@ DownloadHandle* getDownloadHandle(Session* session, A2Gid gid)
       return new DownloadResultDH(ds);
     }
   }
-  return 0;
+  return nullptr;
 }
 
 void deleteDownloadHandle(DownloadHandle* dh)
diff --git a/src/metalink_helper.cc b/src/metalink_helper.cc
index bebbc0f7..9a24fe40 100644
--- a/src/metalink_helper.cc
+++ b/src/metalink_helper.cc
@@ -143,7 +143,7 @@ std::unique_ptr<Metalinker> parseBinaryStream
     offread += nread;
   }
   if(nread == 0 && retval) {
-    if(ps.parseFinal(0, 0) < 0) {
+    if(ps.parseFinal(nullptr, 0) < 0) {
       retval = false;
     }
   }
diff --git a/src/util.cc b/src/util.cc
index c53c09aa..0d6621fe 100644
--- a/src/util.cc
+++ b/src/util.cc
@@ -867,7 +867,7 @@ ssize_t parse_content_disposition(char *dest, size_t destlen,
                                   const char **charsetp, size_t *charsetlenp,
                                   const char *in, size_t len)
 {
-  const char *p = in, *eop = in + len, *mark_first = NULL, *mark_last = NULL;
+  const char *p = in, *eop = in + len, *mark_first = nullptr, *mark_last = nullptr;
   int state = CD_BEFORE_DISPOSITION_TYPE;
   int in_file_parm = 0;
   int flags = 0;
@@ -880,7 +880,7 @@ ssize_t parse_content_disposition(char *dest, size_t destlen,
   uint32_t dfa_code = 0;
   uint8_t pctval = 0;
 
-  *charsetp = NULL;
+  *charsetp = nullptr;
   *charsetlenp = 0;
 
   for(; p != eop; ++p) {
@@ -1226,7 +1226,7 @@ bool isNumericHost(const std::string& name)
   memset(&hints, 0, sizeof(hints));
   hints.ai_family = AF_UNSPEC;
   hints.ai_flags = AI_NUMERICHOST;
-  if(getaddrinfo(name.c_str(), 0, &hints, &res)) {
+  if(getaddrinfo(name.c_str(), nullptr, &hints, &res)) {
     return false;
   }
   freeaddrinfo(res);
@@ -1315,7 +1315,7 @@ void setGlobalSignalHandler(int sig, sigset_t* mask, signal_handler_t handler,
   sigact.sa_handler = handler;
   sigact.sa_flags = flags;
   sigact.sa_mask = *mask;
-  sigaction(sig, &sigact, NULL);
+  sigaction(sig, &sigact, nullptr);
 #else
   signal(sig, handler);
 #endif // HAVE_SIGACTION
@@ -1847,13 +1847,13 @@ void executeHook
   cmdlineLen = utf8ToWChar(wcharCmdline.get(), cmdlineLen, cmdline.c_str());
   assert(cmdlineLen > 0);
   A2_LOG_INFO(fmt("Executing user command: %s", cmdline.c_str()));
-  DWORD rc = CreateProcessW(batch ? utf8ToWChar(cmdexe).c_str() : NULL,
+  DWORD rc = CreateProcessW(batch ? utf8ToWChar(cmdexe).c_str() : nullptr,
                             wcharCmdline.get(),
-                            NULL,
-                            NULL,
+                            nullptr,
+                            nullptr,
                             true,
                             0,
-                            NULL,
+                            nullptr,
                             0,
                             &si,
                             &pi);
diff --git a/test/DefaultBtProgressInfoFileTest.cc b/test/DefaultBtProgressInfoFileTest.cc
index 9fefb8e4..974c0555 100644
--- a/test/DefaultBtProgressInfoFileTest.cc
+++ b/test/DefaultBtProgressInfoFileTest.cc
@@ -557,7 +557,7 @@ void DefaultBtProgressInfoFileTest::testUpdateFilename()
   std::shared_ptr<DownloadContext> dctx
     (new DownloadContext(1024, 81920, A2_TEST_DIR"/file1"));
 
-  DefaultBtProgressInfoFile infoFile(dctx, std::shared_ptr<MockPieceStorage>(), 0);
+  DefaultBtProgressInfoFile infoFile(dctx, std::shared_ptr<MockPieceStorage>(), nullptr);
 #ifdef ENABLE_BITTORRENT
   infoFile.setBtRuntime(btRuntime_);
   infoFile.setPeerStorage(peerStorage_);
diff --git a/test/GZipDecoder.cc b/test/GZipDecoder.cc
index a88faa2a..12aab74c 100644
--- a/test/GZipDecoder.cc
+++ b/test/GZipDecoder.cc
@@ -40,7 +40,7 @@ namespace aria2 {
 
 const std::string GZipDecoder::NAME("GZipDecoder");
 
-GZipDecoder::GZipDecoder():strm_(0), finished_(false) {}
+GZipDecoder::GZipDecoder():strm_(nullptr), finished_(false) {}
 
 GZipDecoder::~GZipDecoder()
 {
@@ -69,7 +69,7 @@ void GZipDecoder::release()
   if(strm_) {
     inflateEnd(strm_);
     delete strm_;
-    strm_ = 0;
+    strm_ = nullptr;
   }
 }
 
diff --git a/test/GrowSegmentTest.cc b/test/GrowSegmentTest.cc
index 97b0509c..c973a39e 100644
--- a/test/GrowSegmentTest.cc
+++ b/test/GrowSegmentTest.cc
@@ -37,7 +37,7 @@ void GrowSegmentTest::testClear()
   GrowSegment segment(std::shared_ptr<Piece>(new Piece()));
   segment.updateWrittenLength(32*1024);
   CPPUNIT_ASSERT_EQUAL(32*1024, segment.getWrittenLength());
-  segment.clear(0);
+  segment.clear(nullptr);
   CPPUNIT_ASSERT_EQUAL(0, segment.getWrittenLength());
 }
 
diff --git a/test/IndexedListTest.cc b/test/IndexedListTest.cc
index e208005b..23d19ab3 100644
--- a/test/IndexedListTest.cc
+++ b/test/IndexedListTest.cc
@@ -229,7 +229,7 @@ void IndexedListTest::testGet()
   int b = 1;
   list.push_back(123, &a);
   list.push_back(1, &b);
-  CPPUNIT_ASSERT_EQUAL((int*)0, list.get(1000));
+  CPPUNIT_ASSERT_EQUAL((int*)nullptr, list.get(1000));
   CPPUNIT_ASSERT_EQUAL(&a, list.get(123));
 }
 
diff --git a/test/MultiDiskAdaptorTest.cc b/test/MultiDiskAdaptorTest.cc
index 001c9a54..75e748fe 100644
--- a/test/MultiDiskAdaptorTest.cc
+++ b/test/MultiDiskAdaptorTest.cc
@@ -270,7 +270,7 @@ void MultiDiskAdaptorTest::testResetDiskWriterEntries()
 
 void readFile(const std::string& filename, char* buf, int bufLength) {
   FILE* f = fopen(filename.c_str(), "r");
-  if(f == NULL) {
+  if(f == nullptr) {
     CPPUNIT_FAIL(strerror(errno));
   }
   int retval = fread(buf, bufLength, 1, f);
diff --git a/test/RpcMethodTest.cc b/test/RpcMethodTest.cc
index 902a1c3a..15a94b45 100644
--- a/test/RpcMethodTest.cc
+++ b/test/RpcMethodTest.cc
@@ -684,7 +684,7 @@ void RpcMethodTest::testChangeGlobalOption_withNotAllowedOption()
 void RpcMethodTest::testNoSuchMethod()
 {
   NoSuchMethodRpcMethod m;
-  auto res = m.execute(createReq("make.hamburger"), 0);
+  auto res = m.execute(createReq("make.hamburger"), nullptr);
   CPPUNIT_ASSERT_EQUAL(1, res.code);
   CPPUNIT_ASSERT_EQUAL(std::string("No such method: make.hamburger"),
                        getString(downcast<Dict>(res.param), "faultString"));
diff --git a/test/SegmentTest.cc b/test/SegmentTest.cc
index 061cb891..0f32e310 100644
--- a/test/SegmentTest.cc
+++ b/test/SegmentTest.cc
@@ -68,7 +68,7 @@ void SegmentTest::testClear()
   PiecedSegment s(16*1024*10, p);
   s.updateWrittenLength(16*1024*10);
   CPPUNIT_ASSERT_EQUAL(16*1024*10, s.getWrittenLength());
-  s.clear(0);
+  s.clear(nullptr);
   CPPUNIT_ASSERT_EQUAL(0, s.getWrittenLength());
 }
 
diff --git a/test/SocketCoreTest.cc b/test/SocketCoreTest.cc
index 064a5141..6f44b093 100644
--- a/test/SocketCoreTest.cc
+++ b/test/SocketCoreTest.cc
@@ -87,7 +87,7 @@ void SocketCoreTest::testInetNtop()
   {
     std::string s = "192.168.0.1";
     addrinfo* res;
-    CPPUNIT_ASSERT_EQUAL(0, callGetaddrinfo(&res, s.c_str(), 0, AF_INET,
+    CPPUNIT_ASSERT_EQUAL(0, callGetaddrinfo(&res, s.c_str(), nullptr, AF_INET,
                                             SOCK_STREAM, 0, 0));
     std::unique_ptr<addrinfo, decltype(&freeaddrinfo)> resDeleter
       (res, freeaddrinfo);
@@ -100,7 +100,7 @@ void SocketCoreTest::testInetNtop()
   {
     std::string s = "2001:db8::2:1";
     addrinfo* res;
-    CPPUNIT_ASSERT_EQUAL(0, callGetaddrinfo(&res, s.c_str(), 0, AF_INET6,
+    CPPUNIT_ASSERT_EQUAL(0, callGetaddrinfo(&res, s.c_str(), nullptr, AF_INET6,
                                             SOCK_STREAM, 0, 0));
     std::unique_ptr<addrinfo, decltype(&freeaddrinfo)> resDeleter
       (res, freeaddrinfo);
diff --git a/test/TimeTest.cc b/test/TimeTest.cc
index b1835716..0a56f21d 100644
--- a/test/TimeTest.cc
+++ b/test/TimeTest.cc
@@ -113,7 +113,7 @@ void TimeTest::testToHTTPDate()
 void TimeTest::testElapsed()
 {
   struct timeval now;
-  gettimeofday(&now, 0);
+  gettimeofday(&now, nullptr);
   {
     struct timeval tv = now;
     CPPUNIT_ASSERT(!Time(tv).elapsed(1));
diff --git a/test/UriSplitTest.cc b/test/UriSplitTest.cc
index bb129091..3016031d 100644
--- a/test/UriSplitTest.cc
+++ b/test/UriSplitTest.cc
@@ -391,28 +391,28 @@ void UriSplitTest::testUriSplit()
 
 void UriSplitTest::testUriSplit_fail()
 {
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, ""));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "h"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http:"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http:a"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http:/"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http:/a"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://:host"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://@user@host"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:pass"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:65536"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:pass?"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:pass@host:65536"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:pass@host:x"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:pass@host:80x"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user@"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://[]"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://[::"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user[::1]"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user[::1]x"));
-  CPPUNIT_ASSERT_EQUAL(-1, uri_split(NULL, "http://user:pass[::1]"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, ""));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "h"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http:"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http:a"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http:/"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http:/a"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://:host"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://@user@host"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:pass"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:65536"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:pass?"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:pass@host:65536"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:pass@host:x"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:pass@host:80x"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user@"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://[]"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://[::"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user[::1]"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user[::1]x"));
+  CPPUNIT_ASSERT_EQUAL(-1, uri_split(nullptr, "http://user:pass[::1]"));
 }
 
 } // namespace aria2