THRIFT-706. cpp: Fix memory leak of string_buf_ in TCompactProtocol

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@920597 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/cpp/src/protocol/TCompactProtocol.h b/lib/cpp/src/protocol/TCompactProtocol.h
index b4e06f0..1d940a2 100644
--- a/lib/cpp/src/protocol/TCompactProtocol.h
+++ b/lib/cpp/src/protocol/TCompactProtocol.h
@@ -109,6 +109,9 @@
     boolValue_.hasBoolValue = false;
   }
 
+  ~TCompactProtocol() {
+    free(string_buf_);
+  }
 
 
   /**