[dns-client] remove memset(zero) from constructor (#4195)

src/core/net/dns_client.cpp

@@ -49,6 +49,30 @@ using ot::Encoding::BigEndian::HostSwap16;
 namespace ot {
 namespace Dns {
 
+QueryMetadata::QueryMetadata(void)
+    : mHostname(NULL)
+    , mResponseHandler(NULL)
+    , mResponseContext(NULL)
+    , mTransmissionTime()
+    , mDestinationPort(0)
+    , mRetransmissionCount(0)
+{
+    mSourceAddress.Clear();
+    mDestinationAddress.Clear();
+}
+
+QueryMetadata::QueryMetadata(otDnsResponseHandler aHandler, void *aContext)
+    : mHostname(NULL)
+    , mResponseHandler(aHandler)
+    , mResponseContext(aContext)
+    , mTransmissionTime()
+    , mDestinationPort(0)
+    , mRetransmissionCount(0)
+{
+    mSourceAddress.Clear();
+    mDestinationAddress.Clear();
+}
+
 Client::Client(Ip6::Netif &aNetif)
     : mSocket(aNetif.Get<Ip6::Udp>())
     , mMessageId(0)

src/core/net/dns_client.hpp

@@ -60,7 +60,7 @@ public:
      * Default constructor for the object.
      *
      */
-    QueryMetadata(void) { memset(this, 0, sizeof(*this)); }
+    QueryMetadata(void);
 
     /**
      * This constructor initializes the object with specific values.
@@ -69,12 +69,7 @@ public:
      * @param[in]  aContext  Context for the handler function.
      *
      */
-    QueryMetadata(otDnsResponseHandler aHandler, void *aContext)
-    {
-        memset(this, 0, sizeof(*this));
-        mResponseHandler = aHandler;
-        mResponseContext = aContext;
-    }
+    QueryMetadata(otDnsResponseHandler aHandler, void *aContext);
 
     /**
      * This method appends request data to the message.