Attempting MQTT connection...Failed when connecting to MQTT using variables

Projects Programming
1

Hey all,

So I'm trying to use variables to set up my PubSubClient connection. When the port is hard coded, it seems fine but when I use a variable then it fails to connect:

Below shows the 2 methods I'm trying. The first one uses (int)mqtt_port and fails to connect. The second has it hard coded and works fine.

char mqtt_ip[16] = "192.168.1.82";
char mqtt_port[7] = "1883";
//This one doesn't work. When I try to connect I get message:
//  Attempting MQTT connection...	Failed.
PubSubClient client(mqtt_ip, (int)mqtt_port, callback, wifiClient);

//This one works fine
PubSubClient client(MQTT_SERVER, 1883, callback, wifiClient);

Can anyone tell me what's wrong here?

Thanks,
Cheese

2

Why are you trying to cast a constant string to an int ?

Have you tried printing (int)mqtt_port) ?

3

iow, how about char mqtt_port[7] = "1883\0";
and using atoi(mqqt_port) There must be a reason for wanting it as a c-string initially, i hope.

4

There must be a reason for wanting it as a c-string initially, i hope.

I await the reply with bated breath

char mqtt_port[7] = "1883\0";

No need for the explicit terminator as the compiler will add one anyway. Nor any need for the array size specifier either unless it is to be used to hold a longer string later

5

No need for the explicit terminator as the compiler will add one anyway.

I'm never really sure about that, i know it does for a char *, and won't hurt might help.

6

won't hurt might help.

Unless for some reason later in the code you need to know the actual length of the string

7

UKHeliBob:
I await the reply with bated breath

I don't know about the OP, but I frequently reuse code for my Home IOT projects, and if I forget to make the pubSub client name unique, one or both fail to work.

8

Deva_Rishi:
iow, how about

char mqtt_port[7] = "1883\0";

and using

atoi(mqqt_port)

There must be a reason for wanting it as a c-string initially, i hope.

Thankyou. This did the job. There was no need to terminate it though.

As for the reason to use a c-string, I really can't tell you why. I think I got the code snippet from the WIFIManager GitHub for adding additional parameters. I'm no expert so I just followed that guidance. May or may not be right but it sure was a painful way to do it. :stuck_out_tongue:

Thanks again.

9

char mqtt_ip[16] = "192.168.1.82";I sort of understand it for an IP address that you may want to show in the SM or on a page (i tend to keep a copy as a String as well) though there is a struct available called IPAddress theIP = IPAddress(192,168,4,1);