While trying to setup an ESP32 as mqtt publisher I am getting strange errors. Here is my code:

#include "mqttSetup.h"
#include <WiFi.h>
#include <PubSubClient.h>

static byte httpFailCounter = 0;
byte counter = 0;

const char *ssid = "SSID";
// const char *password = "xxxxx";
const char *passphrase = "xxxxx";

WiFiClient espClient;

const char *mqtt_server = "";
const int mqttPort = 1883;
const char *mqttUser = "xxxx";
const char *mqttPassword = "xxxxx";

PubSubClient pubClient(espClient);

pubClient.setServer(mqtt_server, mqttPort); 

void checkConnection()
    if (WiFi.status() == WL_CONNECTED)
        counter = 0; //reset counter
    else if (WiFi.status() != WL_CONNECTED)
        WiFi.begin(ssid, passphrase);
    while (WiFi.status() != WL_CONNECTED)

        if (counter >= 60)

void reconnect()
    while (!pubClient.connected())
        Serial.print("Attempting MQTT connection...");
        // Create a random client ID
        const char *clientID = "ESP32D-MQTT";
        // Attempt to connect
        if (pubClient.connect(clientID))
            // Once connected, publish an announcement...
            pubClient.publish("outTopic", "Hello from ESP");
            // ... and resubscribe
            //   client.subscribe("inTopic");
            Serial.print("failed, rc=");
            Serial.println(" try again in 5 seconds");
            // Wait 5 seconds before retrying

I don't understand why the compiler is spitting out the following two errors:

this declaration has no storage class or type specifier (referring to my pubClient declaration)

expected a ';'

It doesn't have any issue when I declare the pubClient but at the line :

pubClient.setServer(mqtt_server, mqttPort);

where I use the pubClient it gives the error.

Besides I don't see any ; missing in the code.

Could you please help me figure out the source of error?

Header file for this code chunk


void checkConnection();
void reconnect();


------------ Main sketch---------

#include <Arduino.h>
#include "Wire.h"
#include "tempSensor.h"
#include "mqttSetup.h"

void setup()

  while (!Serial)


void loop()
  uint32_t newTime = millis();
  static uint32_t oldTime = 0;
  static uint32_t t2 = 0;

  float temp = 0.0;
  float humid = 0.0;

  char senVals[50];

  if (newTime - oldTime >= 10000)
    oldTime = newTime;

    readsht(temp, humid);
    snprintf(senVals, 50, "Temp: %.2f Humid: %.2f", temp, humid);


1 Answer 1


Code goes in functions, not the global scope.

Your line

pubClient.setServer(mqtt_server, mqttPort);

should be inside a function. Most probably setup() so it gets called when your program starts.

Incidentally - where are setup() and loop() - the two functions that are required by Arduino code?

  • This code chunk is contained in a separate .cpp file. I was trying to keep the main sketch clean from setup and function definitions for different components. That's why you don't see the main sketch. I intended to call only a publish function(not yet implemented in my code) in the main sketch. I will update my post with the header file and the main sketch
    – Zaffresky
    Jan 22, 2021 at 14:18
  • @Zaffresky Then you should wrap that line in a function which you can then call from setup().
    – Majenko
    Jan 22, 2021 at 14:19
  • I have updated my post with main sketch and the relevant header file. I don't fully understand why I should put the line "PubClient.setServer(mqtt_server, mqttPort);" in a new function. My understanding was that the PubClinet.serServer function is already defined in the PubSubClient library and in my separate mqttSetup.cpp file I was calling this function so that this file would be self-contained and I wouldn't need to call any PubSubClient library functions directly in the main sketch. Rather I would only call my function publishMQTT() in the main sketch. Is this approach wrong?
    – Zaffresky
    Jan 22, 2021 at 14:30
  • 1
    @Zaffresky Because code goes in functions not in the global scope. Anything you call during the sequence of the execution of your program must go in a function. The only things that can go in the global scope are variable declarations (with or without an immediate assignment).
    – Majenko
    Jan 22, 2021 at 14:41
  • I see it now. I was not considering the scope in that seperate .cpp file. I mistakenly assumed that the concept of scope was applicable only to the main sketch. Thanks for clarifying
    – Zaffresky
    Jan 22, 2021 at 14:49

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