THRIFT-1566 Thrift/cpp: Use some different string operations

git-svn-id: https://svn.apache.org/repos/asf/thrift/trunk@1325792 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/cpp/src/thrift/protocol/TBinaryProtocol.tcc b/lib/cpp/src/thrift/protocol/TBinaryProtocol.tcc
index 721e897..a95fdba 100644
--- a/lib/cpp/src/thrift/protocol/TBinaryProtocol.tcc
+++ b/lib/cpp/src/thrift/protocol/TBinaryProtocol.tcc
@@ -428,7 +428,7 @@
 
   // Catch empty string case
   if (size == 0) {
-    str = "";
+    str.clear();
     return result;
   }
 
@@ -451,7 +451,7 @@
     this->string_buf_size_ = size;
   }
   this->trans_->readAll(this->string_buf_, size);
-  str = std::string((char*)this->string_buf_, size);
+  str.assign((char*)this->string_buf_, size);
   return (uint32_t)size;
 }