Arduino ESP8266 01 MQTT Raspberry pi - mqtt

Question

I want to use ESP 8266 01 and arduino uno as client in MQTT. The code For ESP8266 01 is successfully compiled and I'M getting errors in Arduino uno
The error is 'messageTemp' was not declared in this scope
Amd also I have a thought of using stm32xx in client.
If I compile for that
exit status 1
ISO C++ forbids comparison between pointer and integer [-fpermissive]
above is the error I'm getting
1)ESP code
// Loading the ESP8266WiFi library and the PubSubClient library
#include <ESP8266WiFi.h>
#include <PubSubClient.h>
// Change the credentials below, so your ESP8266 connects to your router
const char* ssid = "YOUR_SSID";
const char* password = "YOUR_PASSWORD";
const char* mqtt_server = "YOUR_RPi_IP_Address";
// Initializes the espClient
WiFiClient espClient;
PubSubClient client(espClient);
void setup_wifi() {
delay(10);
// We start by connecting to a WiFi network
Serial.println();
Serial.print("Connecting to ");
Serial.println(ssid);
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(500);
Serial.print(".");
}
Serial.println("");
Serial.print("WiFi connected - ESP IP address: ");
Serial.println(WiFi.localIP());
}
if(topic=="home/office/esp1/gpio2"){
Serial.print("Changing GPIO 2 to ");
if(messageTemp == "1"){
// digitalWrite(ledGPIO2, HIGH);
Serial.print("On");
}
else if(messageTemp == "0"){
// digitalWrite(ledGPIO2, LOW);
Serial.print("Off");
}
}
Serial.println();
}
void reconnect() {
// Loop until we're reconnected
while (!client.connected()) {
Serial.print("Attempting MQTT connection...");
// Attempt to connect
if (client.connect("ESP8266Client")) {
Serial.println("connected");
client.subscribe("home/office/esp1/gpio2");
}
else
{
Serial.print("failed, rc=");
Serial.print(client.state());
Serial.println(" try again in 5 seconds");
// Wait 5 seconds before retrying
delay(5000);
}
}
}
void setup() {
Serial.begin(115200);
setup_wifi();
client.setServer(mqtt_server, 1883);
client.setCallback(callback);
}
void loop() {
if (!client.connected()) {
reconnect();
}
client.loop();
}
Code for Arduino UNO
void setup(){
Serial.begin(9600);
pinMode(12, OUTPUT);
digitalWrite(12, HIGH);
String messageTemp;
}
void callback(String topic, byte* message, unsigned int length) {
Serial.print("Message arrived on topic: ");
Serial.print(topic);
Serial.print(". Message: ");
String messageTemp;
for (int i = 0; i < length; i++) {
Serial.print((char)message[i]);
messageTemp += (char)message[i];
}
Serial.println();
}
void loop ()
{
if (Serial.available()){
char topic = Serial.read();
{
if (topic=="home/office/esp1/gpio2")
{
Serial.print("Changing GPIO 2 to ");
if(messageTemp == "1"){
digitalWrite(12, HIGH);
Serial.print("On");
}
else if(messageTemp == "0")
{
digitalWrite(12, LOW);
Serial.print("Off");
}
}}}}

Answer 1

ESP code doesn't look the whole source code you provided. In case of Arduino UNO, if you're intending to use messageTemp as a global variable, then you need to declare it only one time outside of functions. In the above code, you declared it twice in setup() and callback(), then those are considered as local variables. Even in loop(), there's no declaration, this should create the compile error.