Prefer specific [io]stringstream where possible

These better communicate intent and are slightly more efficient.

src/addhead.cpp

@@ -93,7 +93,7 @@ bool AdditionalHeader::Load(const char* file)
       continue;
     }
     // load a line
-    stringstream ss(line);
+    istringstream ss(line);
     string        key;           // suffix(key)
     string        head;          // additional HTTP header
     string        value;         // header value
@@ -245,7 +245,7 @@ bool AdditionalHeader::Dump(void) const
     return true;
   }
 
-  stringstream ssdbg;
+  ostringstream ssdbg;
   int           cnt = 1;
 
   ssdbg << "Additional Header list[" << addheadlist.size() << "] = {" << endl;

src/curl.cpp

@@ -611,7 +611,7 @@ bool S3fsCurl::InitMimeType(const char* MimeFile)
         continue;
       }
 
-      stringstream tmp(line);
+      istringstream tmp(line);
       string mimeType;
       tmp >> mimeType;
       while(tmp){
@@ -808,7 +808,7 @@ size_t S3fsCurl::HeaderCallback(void* data, size_t blockSize, size_t numBlocks,
   headers_t* headers = reinterpret_cast<headers_t*>(userPtr);
   string header(reinterpret_cast<char*>(data), blockSize * numBlocks);
   string key;
-  stringstream ss(header);
+  istringstream ss(header);
 
   if(getline(ss, key, ':')){
     // Force to lower, only "x-amz"
@@ -3681,7 +3681,7 @@ int S3fsCurl::MultipartHeadRequest(const char* tpath, off_t size, headers_t& met
   off_t          chunk;
   off_t          bytes_remaining;
   etaglist_t     list;
-  stringstream   strrange;
+  ostringstream  strrange;
 
   S3FS_PRN_INFO3("[tpath=%s]", SAFESTRPTR(tpath));
 
@@ -3814,7 +3814,7 @@ int S3fsCurl::MultipartRenameRequest(const char* from, const char* to, headers_t
   off_t          chunk;
   off_t          bytes_remaining;
   etaglist_t     list;
-  stringstream   strrange;
+  ostringstream  strrange;
 
   S3FS_PRN_INFO3("[from=%s][to=%s]", SAFESTRPTR(from), SAFESTRPTR(to));
 

src/fdcache.cpp

@@ -503,7 +503,7 @@ bool PageList::Serialize(CacheFileStat& file, bool is_output)
     //
     // put to file
     //
-    stringstream ssall;
+    ostringstream ssall;
     ssall << Size();
 
     for(fdpage_list_t::iterator iter = pages.begin(); iter != pages.end(); ++iter){
@@ -544,7 +544,7 @@ bool PageList::Serialize(CacheFileStat& file, bool is_output)
       return false;
     }
     string        oneline;
-    stringstream ssall(ptmp);
+    istringstream ssall(ptmp);
 
     // loaded
     Clear();
@@ -561,7 +561,7 @@ bool PageList::Serialize(CacheFileStat& file, bool is_output)
     bool is_err = false;
     while(getline(ssall, oneline, '\n')){
       string        part;
-      stringstream ssparts(oneline);
+      istringstream ssparts(oneline);
       // offset
       if(!getline(ssparts, part, ':')){
         is_err = true;

src/s3fs_util.cpp

@@ -611,7 +611,7 @@ int mkdirp(const string& path, mode_t mode)
 {
   string        base;
   string        component;
-  stringstream ss(path);
+  istringstream ss(path);
   while (getline(ss, component, '/')) {
     base += "/" + component;
 
@@ -635,7 +635,7 @@ string get_exist_directory_path(const string& path)
   string        existed("/");    // "/" is existed.
   string        base;
   string        component;
-  stringstream ss(path);
+  istringstream ss(path);
   while (getline(ss, component, '/')) {
     if(base != "/"){
       base += "/";

src/string_util.cpp

@@ -33,7 +33,7 @@
 using namespace std;
 
 template <class T> std::string str(T value) {
-  std::stringstream s;
+  std::ostringstream s;
   s << value;
   return s.str();
 }