[settings] add Clear() method for all setting structures (#4315)

src/core/common/settings.hpp

@@ -86,6 +86,12 @@ public:
      */
     struct NetworkInfo
     {
+        /**
+         * This method clears the struct object (setting all the fields to zero).
+         *
+         */
+        void Clear(void) { memset(this, 0, sizeof(*this)); }
+
         uint8_t         mRole;                   ///< Current Thread role.
         uint8_t         mDeviceMode;             ///< Device mode setting.
         uint16_t        mRloc16;                 ///< RLOC16
@@ -103,6 +109,12 @@ public:
      */
     struct ParentInfo
     {
+        /**
+         * This method clears the struct object (setting all the fields to zero).
+         *
+         */
+        void Clear(void) { memset(this, 0, sizeof(*this)); }
+
         Mac::ExtAddress mExtAddress; ///< Extended Address
     };
 
@@ -112,6 +124,12 @@ public:
      */
     struct ChildInfo
     {
+        /**
+         * This method clears the struct object (setting all the fields to zero).
+         *
+         */
+        void Clear(void) { memset(this, 0, sizeof(*this)); }
+
         Mac::ExtAddress mExtAddress; ///< Extended Address
         uint32_t        mTimeout;    ///< Timeout
         uint16_t        mRloc16;     ///< RLOC16

src/core/thread/mle.cpp

@@ -447,7 +447,7 @@ otError Mle::Store(void)
     otError               error = OT_ERROR_NONE;
     Settings::NetworkInfo networkInfo;
 
-    memset(&networkInfo, 0, sizeof(networkInfo));
+    networkInfo.Clear();
 
     if (IsAttached())
     {
@@ -465,7 +465,7 @@ otError Mle::Store(void)
         {
             Settings::ParentInfo parentInfo;
 
-            memset(&parentInfo, 0, sizeof(parentInfo));
+            parentInfo.Clear();
             parentInfo.mExtAddress = mParent.GetExtAddress();
 
             SuccessOrExit(error = Get<Settings>().SaveParentInfo(parentInfo));

src/core/thread/mle_router.cpp

@@ -3571,7 +3571,7 @@ otError MleRouter::StoreChild(const Child &aChild)
 
     IgnoreReturnValue(RemoveStoredChild(aChild.GetRloc16()));
 
-    memset(&childInfo, 0, sizeof(childInfo));
+    childInfo.Clear();
     childInfo.mExtAddress = aChild.GetExtAddress();
     childInfo.mTimeout    = aChild.GetTimeout();
     childInfo.mRloc16     = aChild.GetRloc16();