sudoku_base is a piece of code that solves Sudoku puzzles. As the name suggests, sudoku_base is the backend for solving these puzzles, and is not meant to serve as a frontend.
sudoku_base includes a sample program called sudoku which solves arbitrary puzzles. sudoku is a command line tool that uses the code contained within sudoku_base. To solve puzzles over the command line, you can do something like this.
$ cat data8-hard-inkala.txt
8 ? ? ? ? ? ? ? ?
? ? 3 6 ? ? ? ? ?
? 7 ? ? 9 ? 2 ? ?
? 5 ? ? ? 7 ? ? ?
? ? ? ? 4 5 7 ? ?
? ? ? 1 ? ? ? 3 ?
? ? 1 ? ? ? ? 6 8
? ? 8 5 ? ? ? 1 ?
? 9 ? ? ? ? 4 ? ?
$ ./sudoku < data8-hard-inkala.txt
Read the board in OK.
Here's the current state of the board.
8 ? ? ? ? ? ? ? ?
? ? 3 6 ? ? ? ? ?
? 7 ? ? 9 ? 2 ? ?
? 5 ? ? ? 7 ? ? ?
? ? ? ? 4 5 7 ? ?
? ? ? 1 ? ? ? 3 ?
? ? 1 ? ? ? ? 6 8
? ? 8 5 ? ? ? 1 ?
? 9 ? ? ? ? 4 ? ?
Solving the puzzle...
A solution was found!
8 1 2 7 5 3 6 4 9
9 4 3 6 8 2 1 7 5
6 7 5 4 9 1 2 8 3
1 5 4 2 3 7 8 9 6
3 6 9 8 4 5 7 2 1
2 8 7 1 6 9 5 3 4
5 2 1 9 7 4 3 6 8
4 3 8 5 2 6 9 1 7
7 9 6 3 1 8 4 5 2
This is solving one of the world's hardest Sudoku puzzles in a couple dozen milliseconds.
You can also solve Sudoku puzzles online using a web app I created. It is built on top of Ruby on Rails and sudoku_base. I actually wrote a Ruby Gem that makes use of the code in sudoku_base, so if you want to make your own puzzle solver in Ruby, that's fine too.
Here is the link to the Ruby Gem source code, if you are interested: https://github.com/nealp9084/sudoku_gem . If you are having trouble building it, make sure you have the boost development headers installed.
Here is the link to the web app source code, if you are interested: https://github.com/nealp9084/sudoku_webapp . Since it is a demo, it does not have a lot of features, but it gets the job done.
Last but not least, here is the actual web app: https://www.epicdomain.name