[[fallthrough]] if C++17 only

libi2pd/Garlic.cpp

@@ -911,7 +911,10 @@ namespace garlic
 			case eGarlicDeliveryTypeDestination:
                 LogPrint (eLogDebug, "Garlic: type destination");
 				buf += 32; // TODO: check destination
-				[[fallthrough]]; // no break here
+#if (__cplusplus >= 201703L) // C++ 17 or higher				
+				[[fallthrough]]; 
+#endif				
+				// no break here
 			case eGarlicDeliveryTypeLocal:
 			{
                 LogPrint (eLogDebug, "Garlic: type local");

libi2pd/Identity.cpp

@@ -723,7 +723,10 @@ namespace data
 			case SIGNING_KEY_TYPE_RSA_SHA384_3072:
 			case SIGNING_KEY_TYPE_RSA_SHA512_4096:
 				LogPrint (eLogWarning, "Identity: RSA signature type is not supported. Creating EdDSA");
-				[[fallthrough]]; // no break here
+#if (__cplusplus >= 201703L) // C++ 17 or higher
+				[[fallthrough]]; 
+#endif				
+				// no break here
 			case SIGNING_KEY_TYPE_EDDSA_SHA512_ED25519:
 				i2p::crypto::CreateEDDSA25519RandomKeys (priv, pub);
 			break;

libi2pd/RouterContext.cpp

@@ -338,7 +338,11 @@ namespace i2p
 		{
 			case low   : /* not set */; break;
 			case extra : caps |= i2p::data::RouterInfo::eExtraBandwidth; break; // 'P'
-			case unlim : caps |= i2p::data::RouterInfo::eExtraBandwidth; [[fallthrough]]; //  no break here, extra + high means 'X'
+			case unlim : caps |= i2p::data::RouterInfo::eExtraBandwidth; 
+	#if (__cplusplus >= 201703L) // C++ 17 or higher		
+			[[fallthrough]]; 
+	#endif		
+			//  no break here, extra + high means 'X'
 			case high  : caps |= i2p::data::RouterInfo::eHighBandwidth;  break;
 		}
 		m_RouterInfo.SetCaps (caps);

libi2pd/Streaming.cpp

@@ -847,7 +847,10 @@ namespace stream
 					break;
 					case 2:
 						m_RTO = INITIAL_RTO; // drop RTO to initial upon tunnels pair change first time
-						[[fallthrough]]; // no break here
+#if (__cplusplus >= 201703L) // C++ 17 or higher						
+						[[fallthrough]]; 
+#endif						
+						// no break here
 					case 4:
 						if (m_RoutingSession) m_RoutingSession->SetSharedRoutingPath (nullptr);
 						UpdateCurrentRemoteLease (); // pick another lease

libi2pd_client/SOCKS.cpp

@@ -433,7 +433,9 @@ namespace proxy
 						break;
 						case CMD_UDP:
 							if (m_socksv == SOCKS5) break;
+#if (__cplusplus >= 201703L) // C++ 17 or higher							
 							[[fallthrough]];
+#endif							
 						default:
 							LogPrint(eLogError, "SOCKS: invalid command: ", ((int)*sock_buff));
 							SocksRequestFailed(SOCKS5_GEN_FAIL);