Learning-Bitcoin-from-the-Command-Line/12_2_Accessing_Bitcoind_with_C.md

12.2: Accessing Bitcoind with C

NOTE: This is a draft in progress, so that I can get some feedback from early reviewers. It is not yet ready for learning.

Though command-line curl is the easiest way to access the bitcoind directly, there are many other options for doing so. The best package for doing so in C is currently libbitcoinrpc. It uses a curl library for accessing the data and it uses the somewhat clunky jansson library for decoding JSON. The advantage of a full programming language over command-line curl for writing more complex code should be obvious.

Set Up libbitcoinrpc

First, you need to install a basic C setup and the dependent packages, libcurl, libjansson, and libuuid. The following will do so on a Ubuntu system:

$ sudo apt-get install make
$ sudo apt-get install gcc
$ sudo apt-get install libcurl4-openssl-dev libjansson-dev uuid-dev

You can then download libbitcoinrpc from Github. Clone it or grab a zip file, as you prefer.

$ sudo apt-get unzip
$ unzip libbitcoinrpc-master.zip 
$ cd libbitcoinrpc-master/

Compile libbitcoinrpc

You'll probably need to adjust your $PATH, so that you can access /sbin/ldconfig:

$ PATH="/sbin:$PATH"

You'll also want to adjust the INSTALL_LIBPATH in the Makefile to install to /usr/lib instead of /usr/local/lib:

INSTALL_LIBPATH    := $(INSTALL_PREFIX)/usr/lib

(If you prefer not to sully your /usr/lib, the alternative is to change your etc/ld.so.conf or its dependent files appropriately ... but for a test setup on a test machine, this is probably fine.)

Then you can compile:

$ make

If that works, you can install the package:

$ sudo make install