Fix printing pointer instead of value for changed values.

main.go

@@ -4,6 +4,7 @@ package main
 import (
 	"database/sql"
 	"encoding/json"
+	"fmt"
 	"log"
 	"os"
 	"time"
@@ -139,6 +140,16 @@ func updateFieldIfChanged(currentValue *int, previousValue *int) (*int, bool) {
 	return currentValue, false // Return the original value if it's nil, indicating no change
 }
 
+// safeDerefInt handles potential nil pointers to avoid a runtime panic
+// log messages will display the actual integer values if the pointers are not nil,
+// or "nil" if the pointers are nil.
+func safeDerefInt(ptr *int) string {
+	if ptr != nil {
+		return fmt.Sprintf("%d", *ptr) // Dereference the pointer to get the value
+	}
+	return "nil" // Return a string indicating the value is nil
+}
+
 func mqttMessageHandler(client mqtt.Client, msg mqtt.Message) {
 	// Parse JSON payload
 	var payload Payload
@@ -182,8 +193,10 @@ func mqttMessageHandler(client mqtt.Client, msg mqtt.Message) {
 
 	// If any value has changed, log all the relevant values
 	if changed {
-		log.Printf("Values changed: dt1=%v, dt2=%v, rt1=%v, rt2=%v, g=%v\n",
-			payload.Dt1, payload.Dt2, payload.Rt1, payload.Rt2, payload.G)
+		log.Printf("Values changed: dt1=%s, dt2=%s, rt1=%s, rt2=%s, g=%s\n",
+			safeDerefInt(payload.Dt1), safeDerefInt(payload.Dt2),
+			safeDerefInt(payload.Rt1), safeDerefInt(payload.Rt2),
+			safeDerefInt(payload.G))
 	}
 	// Insert data into PostgreSQL
 	err = insertData(timestamp, payload)