diff --git a/src/addhead.cpp b/src/addhead.cpp
index 1885f2a..1df3533 100644
--- a/src/addhead.cpp
+++ b/src/addhead.cpp
@@ -89,7 +89,7 @@ bool AdditionalHeader::Load(const char* file)
     if('#' == line[0]){
       continue;
     }
-    if(0 == line.size()){
+    if(line.empty()){
       continue;
     }
     // load a line
@@ -108,8 +108,8 @@ bool AdditionalHeader::Load(const char* file)
     }
 
     // check it
-    if(0 == head.size()){
-      if(0 == key.size()){
+    if(head.empty()){
+      if(key.empty()){
         continue;
       }
       S3FS_PRN_ERR("file format error: %s key(suffix) is no HTTP header value.", key.c_str());
diff --git a/src/curl.cpp b/src/curl.cpp
index bb96de3..00fb3c0 100644
--- a/src/curl.cpp
+++ b/src/curl.cpp
@@ -607,7 +607,7 @@ bool S3fsCurl::InitMimeType(const char* MimeFile)
       if(line[0]=='#'){
         continue;
       }
-      if(line.size() == 0){
+      if(line.empty()){
         continue;
       }
 
@@ -617,7 +617,7 @@ bool S3fsCurl::InitMimeType(const char* MimeFile)
       while(tmp){
         string ext;
         tmp >> ext;
-        if(ext.size() == 0){
+        if(ext.empty()){
           continue;
         }
         S3fsCurl::mimeTypes[ext] = mimeType;
@@ -704,7 +704,7 @@ bool S3fsCurl::LocateBundle(void)
   // See if environment variable CURL_CA_BUNDLE is set
   // if so, check it, if it is a good path, then set the
   // curl_ca_bundle variable to it
-  if(0 == S3fsCurl::curl_ca_bundle.size()){
+  if(S3fsCurl::curl_ca_bundle.empty()){
     char* CURL_CA_BUNDLE = getenv("CURL_CA_BUNDLE");
     if(CURL_CA_BUNDLE != NULL)  {
       // check for existence and readability of the file
@@ -960,7 +960,7 @@ storage_class_t S3fsCurl::SetStorageClass(storage_class_t storage_class)
 bool S3fsCurl::PushbackSseKeys(string& onekey)
 {
   onekey = trim(onekey);
-  if(0 == onekey.size()){
+  if(onekey.empty()){
     return false;
   }
   if('#' == onekey[0]){
@@ -1043,7 +1043,7 @@ bool S3fsCurl::SetSseCKeys(const char* filepath)
   while(getline(ssefs, line)){
     S3fsCurl::PushbackSseKeys(line);
   }
-  if(0 == S3fsCurl::sseckeys.size()){
+  if(S3fsCurl::sseckeys.empty()){
     S3FS_PRN_ERR("There is no SSE Key in file(%s).", filepath);
     return false;
   }
@@ -1070,7 +1070,7 @@ bool S3fsCurl::FinalCheckSse(void)
   }else if(SSE_S3 == S3fsCurl::ssetype){
     S3fsCurl::ssekmsid.erase();
   }else if(SSE_C == S3fsCurl::ssetype){
-    if(0 == S3fsCurl::sseckeys.size()){
+    if(S3fsCurl::sseckeys.empty()){
       S3FS_PRN_ERR("sse type is SSE-C, but there is no custom key.");
       return false;
     }
@@ -1105,7 +1105,7 @@ bool S3fsCurl::LoadEnvSseCKeys(void)
   while(getline(fullkeys, onekey, ':')){
     S3fsCurl::PushbackSseKeys(onekey);
   }
-  if(0 == S3fsCurl::sseckeys.size()){
+  if(S3fsCurl::sseckeys.empty()){
     S3FS_PRN_ERR("There is no SSE Key in environment(AWSSSECKEYS=%s).", envkeys);
     return false;
   }
@@ -1566,7 +1566,7 @@ bool S3fsCurl::SetIAMCredentials(const char* response)
 
 bool S3fsCurl::CheckIAMCredentialUpdate(void)
 {
-  if(0 == S3fsCurl::IAM_role.size() && !S3fsCurl::is_ecs && !S3fsCurl::is_ibm_iam_auth){
+  if(S3fsCurl::IAM_role.empty() && !S3fsCurl::is_ecs && !S3fsCurl::is_ibm_iam_auth){
     return true;
   }
   if(time(NULL) + IAM_EXPIRE_MERGIN <= S3fsCurl::AWSAccessTokenExpire){
@@ -1714,7 +1714,7 @@ bool S3fsCurl::ResetHandle(void)
     if(0 == S3fsCurl::ssl_verify_hostname){
       curl_easy_setopt(hCurl, CURLOPT_SSL_VERIFYHOST, 0);
     }
-    if(S3fsCurl::curl_ca_bundle.size() != 0){
+    if(!S3fsCurl::curl_ca_bundle.empty()){
       curl_easy_setopt(hCurl, CURLOPT_CAINFO, S3fsCurl::curl_ca_bundle.c_str());
     }
   }
@@ -2174,7 +2174,7 @@ int S3fsCurl::RequestPerform(void)
 
         // try to locate cert, if successful, then set the
         // option and continue
-        if(0 == S3fsCurl::curl_ca_bundle.size()){
+        if(S3fsCurl::curl_ca_bundle.empty()){
           if(!S3fsCurl::LocateBundle()){
             S3FS_PRN_ERR("could not get CURL_CA_BUNDLE.");
             return -EIO;
@@ -2252,7 +2252,7 @@ string S3fsCurl::CalcSignatureV2(const string& method, const string& strMD5, con
   string Signature;
   string StringToSign;
 
-  if(0 < S3fsCurl::IAM_role.size() || S3fsCurl::is_ecs){
+  if(!S3fsCurl::IAM_role.empty() || S3fsCurl::is_ecs){
     requestHeaders = curl_slist_sort_insert(requestHeaders, "x-amz-security-token", S3fsCurl::AWSAccessToken.c_str());
   }
 
@@ -2290,7 +2290,7 @@ string S3fsCurl::CalcSignature(const string& method, const string& canonical_uri
   string Signature, StringCQ, StringToSign;
   string uriencode;
 
-  if(0 < S3fsCurl::IAM_role.size()  || S3fsCurl::is_ecs){
+  if(!S3fsCurl::IAM_role.empty()  || S3fsCurl::is_ecs){
     requestHeaders = curl_slist_sort_insert(requestHeaders, "x-amz-security-token", S3fsCurl::AWSAccessToken.c_str());
   }
 
@@ -2543,7 +2543,7 @@ int S3fsCurl::GetIAMCredentials(void)
   if (!S3fsCurl::is_ecs && !S3fsCurl::is_ibm_iam_auth) {
     S3FS_PRN_INFO3("[IAM role=%s]", S3fsCurl::IAM_role.c_str());
 
-    if(0 == S3fsCurl::IAM_role.size()) {
+    if(S3fsCurl::IAM_role.empty()) {
       S3FS_PRN_ERR("IAM role name is empty.");
       return -EIO;
     }
diff --git a/src/fdcache.cpp b/src/fdcache.cpp
index 4df92b3..6f7570f 100644
--- a/src/fdcache.cpp
+++ b/src/fdcache.cpp
@@ -176,7 +176,7 @@ bool CacheFileStat::SetPath(const char* tpath, bool is_open)
 
 bool CacheFileStat::Open(void)
 {
-  if(0 == path.size()){
+  if(path.empty()){
     return false;
   }
   if(-1 != fd){
@@ -665,7 +665,7 @@ void FdEntity::Clear(void)
   AutoLock auto_lock(&fdent_lock);
 
   if(-1 != fd){
-    if(0 != cachepath.size()){
+    if(!cachepath.empty()){
       CacheFileStat cfstat(path.c_str());
       if(!pagelist.Serialize(cfstat, true)){
         S3FS_PRN_WARN("failed to save cache stat file(%s).", path.c_str());
@@ -702,7 +702,7 @@ void FdEntity::Close(void)
       refcnt--;
     }
     if(0 == refcnt){
-      if(0 != cachepath.size()){
+      if(!cachepath.empty()){
         CacheFileStat cfstat(path.c_str());
         if(!pagelist.Serialize(cfstat, true)){
           S3FS_PRN_WARN("failed to save cache stat file(%s).", path.c_str());
@@ -834,7 +834,7 @@ int FdEntity::Open(headers_t* pmeta, ssize_t size, time_t time, bool no_fd_lock_
   bool  need_save_csf = false;  // need to save(reset) cache stat file
   bool  is_truncate   = false;  // need to truncate
 
-  if(0 != cachepath.size()){
+  if(!cachepath.empty()){
     // using cache
 
     // open cache and cache stat file, load page info.
@@ -1039,7 +1039,7 @@ int FdEntity::SetMtime(time_t time)
       S3FS_PRN_ERR("futimes failed. errno(%d)", errno);
       return -errno;
     }
-  }else if(0 < cachepath.size()){
+  }else if(!cachepath.empty()){
     // not opened file yet.
     struct utimbuf n_mtime;
     n_mtime.modtime = time;
@@ -1237,7 +1237,7 @@ int FdEntity::NoCacheLoadAndPost(off_t start, size_t size)
   // [NOTE]
   // This method calling means that the cache file is never used no more.
   //
-  if(0 != cachepath.size()){
+  if(!cachepath.empty()){
     // remove cache files(and cache stat file)
     FdManager::DeleteCacheFile(path.c_str());
     // cache file path does not use no more.
@@ -1826,7 +1826,7 @@ bool FdManager::SetCacheDir(const char* dir)
 
 bool FdManager::DeleteCacheDirectory(void)
 {
-  if(0 == FdManager::cache_dir.size()){
+  if(FdManager::cache_dir.empty()){
     return true;
   }
   string cache_path;
@@ -1843,7 +1843,7 @@ int FdManager::DeleteCacheFile(const char* path)
   if(!path){
     return -EIO;
   }
-  if(0 == FdManager::cache_dir.size()){
+  if(FdManager::cache_dir.empty()){
     return 0;
   }
   string cache_path;
@@ -1876,7 +1876,7 @@ int FdManager::DeleteCacheFile(const char* path)
 
 bool FdManager::MakeCachePath(const char* path, string& cache_path, bool is_create_dir, bool is_mirror_path)
 {
-  if(0 == FdManager::cache_dir.size()){
+  if(FdManager::cache_dir.empty()){
     cache_path = "";
     return true;
   }
@@ -1908,7 +1908,7 @@ bool FdManager::MakeCachePath(const char* path, string& cache_path, bool is_crea
 
 bool FdManager::CheckCacheTopDir(void)
 {
-  if(0 == FdManager::cache_dir.size()){
+  if(FdManager::cache_dir.empty()){
     return true;
   }
   string toppath(FdManager::cache_dir + "/" + bucket);
@@ -1938,7 +1938,7 @@ bool FdManager::CheckCacheDirExist(void)
   if(!FdManager::check_cache_dir_exist){
     return true;
   }
-  if(0 == FdManager::cache_dir.size()){
+  if(FdManager::cache_dir.empty()){
     return true;
   }
   // check the directory
@@ -1965,7 +1965,7 @@ uint64_t FdManager::GetFreeDiskSpace(const char* path)
 {
   struct statvfs vfsbuf;
   string         ctoppath;
-  if(0 < FdManager::cache_dir.size()){
+  if(!FdManager::cache_dir.empty()){
     ctoppath = FdManager::cache_dir + "/";
     ctoppath = get_exist_directory_path(ctoppath);	// existed directory
     if(ctoppath != "/"){
@@ -2107,7 +2107,7 @@ FdEntity* FdManager::Open(const char* path, headers_t* pmeta, ssize_t size, time
       // make new obj
       ent = new FdEntity(path, cache_path.c_str());
 
-      if(0 < cache_path.size()){
+      if(!cache_path.empty()){
         // using cache
         fent[string(path)] = ent;
       }else{
diff --git a/src/s3fs.cpp b/src/s3fs.cpp
index 112f659..6dbca11 100644
--- a/src/s3fs.cpp
+++ b/src/s3fs.cpp
@@ -706,7 +706,7 @@ static int check_parent_object_access(const char* path, int mask)
     return 0;
   }
   if(X_OK == (mask & X_OK)){
-    for(parent = mydirname(path); 0 < parent.size(); parent = mydirname(parent)){
+    for(parent = mydirname(path); !parent.empty(); parent = mydirname(parent)){
       if(parent == "."){
         parent = "/";
       }
@@ -2513,7 +2513,7 @@ static int list_bucket(const char* path, S3ObjList& head, const char* delimiter,
 
   while(truncated){
     string each_query = query_delimiter;
-    if(next_marker != ""){
+    if(!next_marker.empty()){
       each_query += "marker=" + urlEncode(next_marker) + "&";
       next_marker = "";
     }
@@ -2679,7 +2679,7 @@ static bool GetXmlNsUrl(xmlDocPtr doc, string& nsurl)
       }
     }
   }
-  if(0 < strNs.size()){
+  if(!strNs.empty()){
     nsurl  = strNs;
     result = true;
   }
@@ -3828,7 +3828,7 @@ static int s3fs_check_service(void)
   s3fscurl.DestroyCurlHandle();
 
   // make sure remote mountpath exists and is a directory
-  if(mount_prefix.size() > 0){
+  if(!mount_prefix.empty()){
     if(remote_mountpath_exists(mount_prefix.c_str()) != 0){
       S3FS_PRN_CRIT("remote mountpath %s not found.", mount_prefix.c_str());
       return EXIT_FAILURE;
@@ -3871,7 +3871,7 @@ static int parse_passwd_file(bucketkvmap_t& resmap)
   // read each line
   while(getline(PF, line)){
     line = trim(line);
-    if(0 == line.size()){
+    if(line.empty()){
       continue;
     }
     if('#' == line[0]){
@@ -3932,7 +3932,7 @@ static int parse_passwd_file(bucketkvmap_t& resmap)
       secret    = trim(iter->substr(first_pos + 1, string::npos));
     }
     if(resmap.end() != resmap.find(bucketname)){
-      S3FS_PRN_EXIT("there are multiple entries for the same bucket(%s) in the passwd file.", ("" == bucketname ? "default" : bucketname.c_str()));
+      S3FS_PRN_EXIT("there are multiple entries for the same bucket(%s) in the passwd file.", (bucketname.empty() ? "default" : bucketname.c_str()));
       return -1;
     }
     kv.clear();
@@ -4038,7 +4038,7 @@ static int read_aws_credentials_file(const std::string &filename)
   string line;
   while(getline(PF, line)){
     line = trim(line);
-    if(0 == line.size()){
+    if(line.empty()){
       continue;
     }
     if('#' == line[0]){
@@ -4129,7 +4129,7 @@ static int read_passwd_file(void)
   }
 
   string bucket_key = allbucket_fields_type;
-  if(0 < bucket.size() && bucketmap.end() != bucketmap.find(bucket)){
+  if(!bucket.empty() && bucketmap.end() != bucketmap.find(bucket)){
     bucket_key = bucket;
   }
   if(bucketmap.end() == bucketmap.find(bucket_key)){
@@ -4183,7 +4183,7 @@ static int get_access_keys(void)
   }
 
   // 2 - was specified on the command line
-  if(passwd_file.size() > 0){
+  if(!passwd_file.empty()){
     ifstream PF(passwd_file.c_str());
     if(PF.good()){
        PF.close();
@@ -4215,7 +4215,7 @@ static int get_access_keys(void)
   AWS_CREDENTIAL_FILE = getenv("AWS_CREDENTIAL_FILE");
   if(AWS_CREDENTIAL_FILE != NULL){
     passwd_file.assign(AWS_CREDENTIAL_FILE);
-    if(passwd_file.size() > 0){
+    if(!passwd_file.empty()){
       ifstream PF(passwd_file.c_str());
       if(PF.good()){
          PF.close();
@@ -4340,7 +4340,7 @@ static int my_fuse_opt_proc(void* data, const char* arg, int key, struct fuse_ar
   int ret;
   if(key == FUSE_OPT_KEY_NONOPT){
     // the first NONOPT option is the bucket name
-    if(bucket.size() == 0){
+    if(bucket.empty()){
       if ((ret = set_bucket(arg))){
         return ret;
       }
@@ -4351,7 +4351,7 @@ static int my_fuse_opt_proc(void* data, const char* arg, int key, struct fuse_ar
     }
 
     // the second NONOPT option is the mountpoint(not utility mode)
-    if(0 == mountpoint.size() && 0 == utility_mode){
+    if(mountpoint.empty() && 0 == utility_mode){
       // save the mountpoint and do some basic error checking
       mountpoint = arg;
       struct stat stbuf;
@@ -5054,7 +5054,7 @@ int main(int argc, char* argv[])
   }
 
   // The first plain argument is the bucket
-  if(bucket.size() == 0){
+  if(bucket.empty()){
     S3FS_PRN_EXIT("missing BUCKET argument.");
     show_usage();
     S3fsCurl::DestroyS3fsCurl();
@@ -5091,7 +5091,7 @@ int main(int argc, char* argv[])
   // readable, non-empty directory, this checks determines
   // if the mountpoint option was ever supplied
   if(utility_mode == 0){
-    if(mountpoint.size() == 0){
+    if(mountpoint.empty()){
       S3FS_PRN_EXIT("missing MOUNTPOINT argument.");
       show_usage();
       S3fsCurl::DestroyS3fsCurl();
@@ -5107,7 +5107,7 @@ int main(int argc, char* argv[])
     s3fs_destroy_global_ssl();
     exit(EXIT_FAILURE);
   }
-  if(passwd_file.size() > 0 && S3fsCurl::IsSetAccessKeys()){
+  if(!passwd_file.empty() && S3fsCurl::IsSetAccessKeys()){
     S3FS_PRN_EXIT("specifying both passwd_file and the access keys options is invalid.");
     S3fsCurl::DestroyS3fsCurl();
     s3fs_destroy_global_ssl();