Arduino. Read two MQTT topics from arduino and store payload of topics at two diferent variable-CodePudding

I new in Arduino! I have two topics on MQTT server, "arduino/temp" and "arduino/humid". On Arduino, I want to store in a two diferent variable, payload of this topics("arduino/temp" and "arduino/humid")

My code is here:

    char myTemp[5];
    char myHum[5];

    void callback(char *topic, byte *payload, unsigned int length) {
    Serial.print("Message arrived in topic: ");
    Serial.println(topic);
//  if(strcmp(topic, "arduino/temp") == 0) {
    if (String(topic) == "arduino/temp") {
    Serial.println(strcmp(topic, "arduino/temp") == 0);
    Serial.print("Message:");
    for (int i = 0; i < length; i  ) {
          Serial.print((char) payload[i]);
          myTemp[i] = (char) payload[i];
      }
      Serial.println();
      Serial.println(myTemp);
      Serial.println("-----------------------");
      }
      else {
      Serial.println(strcmp(topic, "arduino/humid") == 0);
      Serial.print("Message:");
      for (int i = 0; i < length; i  ) {
          Serial.print((char) payload[i]);
          myHum[i] = (char) payload[i];
      }
      Serial.println();
      Serial.println(myHum);
      Serial.println("-----------------------");
      } 
      }

I get correct payload, but i can't asign corectlly to an variablle. This is the result:

    13:08:34.741 -> Message arrived in topic: arduino/temp
    13:08:34.741 -> 1
    13:08:34.741 -> Message: 21.30
    13:08:34.741 ->  21.30
    13:08:34.741 -> -----------------------
    13:08:35.670 -> Message arrived in topic: arduino/humid
    13:08:35.670 -> 1
    13:08:35.670 -> Message: 43.30
    13:08:35.670 ->  43.3021.30
    13:08:35.670 -> -----------------------

Can you help me, please?

CodePudding user response：

A quick fix is adding one more char to both and setting its value to '\0'. This character you are missing is called the null terminator which will let the println() function know that your string has ended.

    char myTemp[6];
    char myHum[6];

    void callback(char *topic, byte *payload, unsigned int length) {
    Serial.print("Message arrived in topic: ");
    Serial.println(topic);
    if (String(topic) == "arduino/temp") {
    Serial.println(strcmp(topic, "arduino/temp") == 0);
    Serial.print("Message:");
    for (int i = 0; i < length; i  ) {
          Serial.print((char) payload[i]);
          myTemp[i] = (char) payload[i];
      }
      myTemp[5] = '\0';
      Serial.println();
      Serial.println(myTemp);
      Serial.println("-----------------------");
      }
      else {
      Serial.println(strcmp(topic, "arduino/humid") == 0);
      Serial.print("Message:");
      for (int i = 0; i < length; i  ) {
          Serial.print((char) payload[i]);
          myHum[i] = (char) payload[i];
      }
      myHum[5] = '\0';
      Serial.println();
      Serial.println(myHum);
      Serial.println("-----------------------");
      } 
      }

Note: you can also test by adding the extra char only and not setting the value up as some compilers will set it to 0 by default.