diff --git a/src/AbstractOptionHandler.h b/src/AbstractOptionHandler.h
index b13c2b2f7..c7faf4b99 100644
--- a/src/AbstractOptionHandler.h
+++ b/src/AbstractOptionHandler.h
@@ -44,7 +44,7 @@
 namespace aria2 {
 
 class Option;
-class Pref;
+struct Pref;
 
 class AbstractOptionHandler : public OptionHandler {
 protected:
diff --git a/src/BitfieldMan.cc b/src/BitfieldMan.cc
index 7fde929b3..bfbc69375 100644
--- a/src/BitfieldMan.cc
+++ b/src/BitfieldMan.cc
@@ -871,7 +871,7 @@ off_t BitfieldMan::getOffsetCompletedLength
 
 off_t BitfieldMan::getMissingUnusedLength(size_t startingIndex) const
 {
-  if(startingIndex < 0 || blocks_ <= startingIndex) {
+  if(blocks_ <= startingIndex) {
     return 0;
   }
   off_t length = 0;
diff --git a/src/DefaultBtProgressInfoFile.cc b/src/DefaultBtProgressInfoFile.cc
index 0698f85a4..a3efb72e5 100644
--- a/src/DefaultBtProgressInfoFile.cc
+++ b/src/DefaultBtProgressInfoFile.cc
@@ -241,8 +241,7 @@ void DefaultBtProgressInfoFile::load()
   if(version >= 1) {
     infoHashLength = ntohl(infoHashLength);
   }
-  if((infoHashLength < 0) ||
-     ((infoHashLength == 0) && infoHashCheckEnabled)) {
+  if(infoHashLength == 0 && infoHashCheckEnabled) {
     throw DL_ABORT_EX(fmt("Invalid info hash length: %d", infoHashLength));
   }
   if(infoHashLength > 0) {
diff --git a/src/DefaultPieceStorage.cc b/src/DefaultPieceStorage.cc
index 867bb3365..a338b6bda 100644
--- a/src/DefaultPieceStorage.cc
+++ b/src/DefaultPieceStorage.cc
@@ -124,7 +124,7 @@ SharedHandle<Piece> DefaultPieceStorage::checkOutPiece
 SharedHandle<Piece> DefaultPieceStorage::getPiece(size_t index)
 {
   SharedHandle<Piece> piece;
-  if(0 <= index && index <= bitfieldMan_->getMaxIndex()) {
+  if(index <= bitfieldMan_->getMaxIndex()) {
     piece = findUsedPiece(index);
     if(!piece) {
       piece.reset(new Piece(index, bitfieldMan_->getBlockLength(index)));
diff --git a/src/DownloadContext.h b/src/DownloadContext.h
index 4f05431b4..5bee68a3e 100644
--- a/src/DownloadContext.h
+++ b/src/DownloadContext.h
@@ -52,7 +52,7 @@ namespace aria2 {
 class RequestGroup;
 class Signature;
 class FileEntry;
-class ContextAttribute;
+struct ContextAttribute;
 
 class DownloadContext
 {
diff --git a/src/HttpResponse.h b/src/HttpResponse.h
index 7e43cb8c1..8695b6a28 100644
--- a/src/HttpResponse.h
+++ b/src/HttpResponse.h
@@ -49,7 +49,7 @@ namespace aria2 {
 class HttpRequest;
 class HttpHeader;
 class StreamFilter;
-class MetalinkHttpEntry;
+struct MetalinkHttpEntry;
 class Option;
 class Checksum;
 
diff --git a/src/LpdMessageReceiver.h b/src/LpdMessageReceiver.h
index 757d98000..c3061fd85 100644
--- a/src/LpdMessageReceiver.h
+++ b/src/LpdMessageReceiver.h
@@ -42,7 +42,7 @@
 namespace aria2 {
 
 class SocketCore;
-class LpdMessage;
+struct LpdMessage;
 
 class LpdMessageReceiver {
 private:
diff --git a/src/MetalinkParserState.h b/src/MetalinkParserState.h
index 54fce4a07..f75c11370 100644
--- a/src/MetalinkParserState.h
+++ b/src/MetalinkParserState.h
@@ -43,7 +43,7 @@
 namespace aria2 {
 
 class MetalinkParserStateMachine;
-class XmlAttr;
+struct XmlAttr;
 
 class MetalinkParserState
 {
diff --git a/src/Option.h b/src/Option.h
index 4d5de4202..a1f71e905 100644
--- a/src/Option.h
+++ b/src/Option.h
@@ -42,7 +42,7 @@
 
 namespace aria2 {
 
-class Pref;
+struct Pref;
 
 class Option {
 private:
diff --git a/src/OptionHandler.h b/src/OptionHandler.h
index 7740b9ce1..3e17ada79 100644
--- a/src/OptionHandler.h
+++ b/src/OptionHandler.h
@@ -57,7 +57,7 @@ extern const std::string PATH_TO_DIR;
 extern const std::string PATH_TO_COMMAND;
 
 class Option;
-class Pref;
+struct Pref;
 
 class OptionHandler {
 public:
diff --git a/src/OptionHandlerException.h b/src/OptionHandlerException.h
index 946475f7c..49c456c92 100644
--- a/src/OptionHandlerException.h
+++ b/src/OptionHandlerException.h
@@ -38,7 +38,7 @@
 
 namespace aria2 {
 
-class Pref;
+struct Pref;
 
 class OptionHandlerException:public RecoverableException {
 private:
diff --git a/src/OptionHandlerImpl.h b/src/OptionHandlerImpl.h
index 22e598b69..b046cd8a6 100644
--- a/src/OptionHandlerImpl.h
+++ b/src/OptionHandlerImpl.h
@@ -44,7 +44,7 @@
 namespace aria2 {
 
 class Option;
-class Pref;
+struct Pref;
 
 class BooleanOptionHandler : public AbstractOptionHandler {
 public:
diff --git a/src/OptionParser.h b/src/OptionParser.h
index 0d05d5687..8d28bbeb9 100644
--- a/src/OptionParser.h
+++ b/src/OptionParser.h
@@ -47,7 +47,7 @@ namespace aria2 {
 
 class Option;
 class OptionHandler;
-class Pref;
+struct Pref;
 
 class OptionParser {
 private:
diff --git a/src/ParserStateMachine.h b/src/ParserStateMachine.h
index abd07b32c..5d0c08d2d 100644
--- a/src/ParserStateMachine.h
+++ b/src/ParserStateMachine.h
@@ -42,7 +42,7 @@
 
 namespace aria2 {
 
-class XmlAttr;
+struct XmlAttr;
 
 class ParserStateMachine {
 public:
diff --git a/src/XmlRpcRequestParserState.h b/src/XmlRpcRequestParserState.h
index 691382340..79b421ee9 100644
--- a/src/XmlRpcRequestParserState.h
+++ b/src/XmlRpcRequestParserState.h
@@ -42,7 +42,7 @@
 
 namespace aria2 {
 
-class XmlAttr;
+struct XmlAttr;
 
 namespace rpc {
 
diff --git a/src/rpc_helper.h b/src/rpc_helper.h
index a4abae5c1..f4c2ba69d 100644
--- a/src/rpc_helper.h
+++ b/src/rpc_helper.h
@@ -43,7 +43,7 @@ namespace aria2 {
 
 namespace rpc {
 
-class RpcRequest;
+struct RpcRequest;
 
 #ifdef ENABLE_XML_RPC
 RpcRequest xmlParseMemory(const char* xml, size_t size);
diff --git a/src/util.h b/src/util.h
index 80de4d299..243a2eebf 100644
--- a/src/util.h
+++ b/src/util.h
@@ -71,7 +71,7 @@ class BinaryStream;
 class FileEntry;
 class RequestGroup;
 class Option;
-class Pref;
+struct Pref;
 
 #define STRTOLL(X) strtoll(X, reinterpret_cast<char**>(0), 10)
 #define STRTOULL(X) strtoull(X, reinterpret_cast<char**>(0), 10)
@@ -111,6 +111,52 @@ std::string nativeToUtf8(const std::string& src);
 
 namespace util {
 
+extern const std::string DEFAULT_STRIP_CHARSET;
+
+template<typename InputIterator>
+std::pair<InputIterator, InputIterator> stripIter
+(InputIterator first, InputIterator last,
+ const std::string& chars = DEFAULT_STRIP_CHARSET)
+{
+  for(; first != last &&
+        std::find(chars.begin(), chars.end(), *first) != chars.end(); ++first);
+  if(first == last) {
+    return std::make_pair(first, last);
+  }
+  InputIterator left = last-1;
+  for(; left != first &&
+        std::find(chars.begin(), chars.end(), *left) != chars.end(); --left);
+  return std::make_pair(first, left+1);
+}
+
+template<typename InputIterator>
+InputIterator lstripIter
+(InputIterator first, InputIterator last, char ch)
+{
+  for(; first != last && *first == ch; ++first);
+  return first;
+}
+
+template<typename InputIterator, typename InputIterator2>
+InputIterator lstripIter
+(InputIterator first, InputIterator last,
+ InputIterator2 cfirst, InputIterator2 clast)
+{
+  for(; first != last && std::find(cfirst, clast, *first) != clast; ++first);
+  return first;
+}
+
+template<typename InputIterator>
+InputIterator lstripIter
+(InputIterator first, InputIterator last)
+{
+  return lstripIter(first, last,
+                    DEFAULT_STRIP_CHARSET.begin(), DEFAULT_STRIP_CHARSET.end());
+}
+
+std::string strip
+(const std::string& str, const std::string& chars = DEFAULT_STRIP_CHARSET);
+
 template<typename InputIterator>
 void divide
 (std::pair<std::pair<InputIterator, InputIterator>,
@@ -161,52 +207,6 @@ std::string itos(int64_t value, bool comma = false);
 int64_t difftv(struct timeval tv1, struct timeval tv2);
 int32_t difftvsec(struct timeval tv1, struct timeval tv2);
 
-extern const std::string DEFAULT_STRIP_CHARSET;
-
-template<typename InputIterator>
-std::pair<InputIterator, InputIterator> stripIter
-(InputIterator first, InputIterator last,
- const std::string& chars = DEFAULT_STRIP_CHARSET)
-{
-  for(; first != last &&
-        std::find(chars.begin(), chars.end(), *first) != chars.end(); ++first);
-  if(first == last) {
-    return std::make_pair(first, last);
-  }
-  InputIterator left = last-1;
-  for(; left != first &&
-        std::find(chars.begin(), chars.end(), *left) != chars.end(); --left);
-  return std::make_pair(first, left+1);
-}
-
-template<typename InputIterator>
-InputIterator lstripIter
-(InputIterator first, InputIterator last, char ch)
-{
-  for(; first != last && *first == ch; ++first);
-  return first;
-}
-
-template<typename InputIterator, typename InputIterator2>
-InputIterator lstripIter
-(InputIterator first, InputIterator last,
- InputIterator2 cfirst, InputIterator2 clast)
-{
-  for(; first != last && std::find(cfirst, clast, *first) != clast; ++first);
-  return first;
-}
-
-template<typename InputIterator>
-InputIterator lstripIter
-(InputIterator first, InputIterator last)
-{
-  return lstripIter(first, last,
-                    DEFAULT_STRIP_CHARSET.begin(), DEFAULT_STRIP_CHARSET.end());
-}
-
-std::string strip
-(const std::string& str, const std::string& chars = DEFAULT_STRIP_CHARSET);
-
 std::string replace(const std::string& target, const std::string& oldstr, const std::string& newstr);
 
 std::string percentEncode(const unsigned char* target, size_t len);
diff --git a/test/array_funTest.cc b/test/array_funTest.cc
index c361bf29c..f922f33d8 100644
--- a/test/array_funTest.cc
+++ b/test/array_funTest.cc
@@ -65,11 +65,11 @@ void array_funTest::testArray_and()
 void array_funTest::testArrayLength()
 {
   int64_t ia[] = { 1, 2, 3, 4, 5 };
-  int64_t zeroLengthArray[] = {};
-
   CPPUNIT_ASSERT_EQUAL((size_t)5, A2_ARRAY_LEN(ia));
-  // This causes compile error under gcc v3.4.3 opensolaris 5.11
-  CPPUNIT_ASSERT_EQUAL((size_t)0, A2_ARRAY_LEN(zeroLengthArray));
+  // This causes compile error under clang and gcc v3.4.3 opensolaris
+  // 5.11
+  // int64_t zeroLengthArray[] = {};
+  // CPPUNIT_ASSERT_EQUAL((size_t)0, A2_ARRAY_LEN(zeroLengthArray));
 }
 
 namespace {