Thursday, September 04, 2014

SparkFun's; libcurl and sqlite on Raspberry Pi

A few months ago SparkFun announced their new data service: There are lots of similar services out there, some really awesome, some simple to use others not so much, some with great charting capabilities, others just a data store but I loved Phant from the beginning, mostly because it doesn't try to do a lot but what it does it does great. Also, its simplicity of use is awesome and is open-source. I was writing a JavaScript application at the time that needed a simple backend storage; I could use almost anything for that storage but when I saw the announcement I quickly decided to give it a try and indeed it was a breeze to post and retrieve data.

Fast forward to now: part of a larger project I am writing with a good friend of mine (in a nutshell an Arduino with DHT and PIR sensors gathers data and sends it using a 433 MHz radio to a Raspberry Pi) I wanted to post the data from a Raspberry Pi to some service on the net so again I chose There are plenty of great examples on SparkFun's tutorial page (and other resources) about how to use Phant with Arduino, Python, Electric Imp but since the code running on my Raspberry Pi is written in C (because this was the simplest code I found for the 433 MHz receiver) I had to figure out how to use Phant using C. I tried for a couple hours to use sockets (found great code examples) but no matter what I did I was getting stuck in all kinds of issues. While looking around on stackoverflow for a solution I found a mention of libcurl - I don't remember who mentioned it but I owe him/her big thanks. I was a little bit reluctant to try it at first since I knew nothing about it but then another mention showed up so I decided to give it a try.

First thing I tried, adding #include <curl/curl.h> ended up with an error at compile time: file not found. So I had to install libcurl dev libraries which was really easy:

sudo apt-get install libcurl4-openssl-dev

and quickly verified that curl was now present in /usr/include/. Then I got the code from the very first example on libcurl page: simple.c but this time I got another error, curl_easy_init not defined or something like it. Another quick search and figured out I had to link the new library so I modified Makefile and added -lcurl. Now everything built and the first try with my test code posted data to The code as it stands today is here part of the repository that will eventually contain all the project code.

libcurl is really awesome: it took only minutes of getting the first version of the code done, in just a few lines (compared to 4 times as much for the socket code), the code is much more readable and the docs are awesome. Thanks to all the authors and contributors for such a great library!

Not completely related to the subject, in the same project I wanted to use a local database on the Raspberry Pi; a quick search got me to sqlite which is very easy to install and there are a lot of articles about it. One thing that most authors don't mention is that same with libcurl there is a library that needs to be installed so sqlite can be used in code and also that is has to be linked for the code to compile. Not a big deal but here are the steps in one place:

sudo apt-get install sqlite3 libsqlite3-dev
compiler link argument: -lsqlite3

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