Need help installing paho.mqtt.c on my raspberry pi

[Anton Gustafsson]

I have an C application on my raspberry pi running Rasbian that needs to publish to a mqtt broker. Now I found this library and wanted to use it. 

I cloned the repository and then ran make and sudo make install and the installation seems to have worked. If I include the header in my C file and compile; #include "MQTTClient.h" it will compile without any problems. Then I added some sample code and compiled again. This time I get a couple of errors sating undefined reference to various methods that should be located in MQTTClient.C  So it seems to me that the linker somehow does find the h file but not the C file. I'm sorry if this is a stupid question, its just that I've been sitting with this for 2 hours now, unable to make it work. 

[Frank Pagliughi]

Try updating the loader cache. Run:

$ sudo ldconfig

Then try to build/link your sample apps again.

Frank

On 12/10/2017 01:56 PM, Anton Gustafsson wrote:

I have an C application on my raspberry pi running Rasbian that needs to publish to a mqtt broker. Now I found this library and wanted to use it. 

I cloned the repository and then ran make and sudo make install and the installation seems to have worked. If I include the header in my C file and compile; #include "MQTTClient.h" it will compile without any problems. Then I added some sample code and compiled again. This time I get a couple of errors sating undefined reference to various methods that should be located in MQTTClient.C  So it seems to me that the linker somehow does find the h file but not the C file. I'm sorry if this is a stupid question, its just that I've been sitting with this for 2 hours now, unable to make it work. 

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[Anton Gustafsson]

Sadly, it seems like I still get the errors:

[Anton Gustafsson]

Think I finally solved it, had to add the library to the compilcation command:  -l paho-mqtt3c

Shouldnt there be a better way though?

[Frank Pagliughi]

Oh, yes. You need to link with one of the Paho C libraries. There are four of them: async or sync, with or with out SSL/TLS. It appears that you're using the synchronous library, so try adding:

-lpaho-mqtt3c

to your compile command. If you're using SSL, use the paho-mqtt3cs library instead.

Frank