W I S C H N E R

In the old days one called g++ compiler with a lot of command line switches to tell it where to find all include files and libraries. Nowadays civilized libraries register themselves with a tool called pkg-config. This tool knows how to generate all command line switches for you if you provide library name.

To list all libraries registered with the tool call

pkg-config –list-all

To see which libraries need to be linked with openssl library use

pkg-config –libs openssl

The tool will output: -lssl -lcrypto which are exactly the command switches you should provide to compiler. So if you wanted to link your sample with the openssl library you could write:

g++ -o sample sample.cpp `pkg-config --libs --cflags openssl`

It really is that simple. Of course you immediately became interested in how exactly pkg-config does its magic, right? After all if you produce a library of your own you want it to be civilized and to register with pkg-config.

Here's how it's done. When you call pkg-config with a library name (for eample libpqxx) it first examines the contents of the /usr/lib/pkgconfig folder seeking for a file named libpqxx.pc. If it can't find it there it examines PKG_CONFIG_PATH variable repeating the search for libpqx.pc in each folder in this path.

After finding a match it extracts required library data. Here is the contents of libpqxx.pc file to get a feeling of how this works.

prefix=/usr/local
exec_prefix=${prefix}
libdir=${exec_prefix}/lib
includedir=${prefix}/include

Name: libpqxx
Description: a C++ API to the PostgreSQL database management system.
Version: 3.0
Libs: -L${libdir} -L/usr/lib -lpqxx
Cflags: -I${includedir} -I/usr/include/postgresql

As you can see data in this description file is abundant. So after matching .pc file with the library pkg-config can easily generate output for command switches.

So there. With tiny bit of new knowledge your library can now register itself properly with the system. You can also create .pc files for libraries that don't behave as good citizens to simplify compilation. Or even debug foreign make files that fail.

.NET spoiled us all. The Framework's Standard Library contains answers to numerous programming challenges. From implementing http client to reading from a database – a plethora of classes speeds up the development and unifies programming experience.

Nothing quite as complete exists for C++. The open source world offers many libraries but without consistency of .NET. Except for two - the C++ Standard Library and the Boost. The latter will soon become part of the former.

Thus start your C++/Unix programming voyage by reading about Boost. Install it on your system. You do not need to compile it on Ubuntu. Just use Synaptic Package Manager to download and install. Then...whenever you identify a programming problem first consult the C++ Standard Library and the Boost. Only if solution can't be found there continue your search elsewhere.

Because the C programming language played such a pivotal role in history of Unix and open source many libraries are written in it. It is quite common to find a pair - a high quality C library to fulfill some task and a C++ wrapper to provide more modern interface.

For example - you might want to implementing http protocol in C++/Unix environment by using the Neon library as underlying technology and the Neon++ wrapper as an actual interface.

Sometimes instead of adding two pluses to wrapper library names an extension mm or xx is used. For example for C library libgtk the C++ wrappers is called libgtkmm. libpango - libpangomm. libcairo - libcairomm. libpg - libpgxx. This convention makes it easier to search for a wrapper when finding a C library to perform a task.

If not too much of a compromise try to keep your code consistent with C++ Coding Convention by selecting libraries that only use combination of lowercase letters and underscores for all program identifiers (except for template parameters, which start with capital letter).

I would like to write a small unix business application.

In .NET I would divide my code it into three packages - user interface, business logic, and database abstracton layer.

User interface would be a simple form application which would host many user controls and take care for communication between them. Its responsibilities would include taking care for dataset flows and responding to events.

Business logic would be further decomposed to client part and business part. Client part would provide user controls that would use facade objects for various business domains. These would communicate with server part of business logic via web service or COM+; using integrated role based security.

Web service would further call business logic dynamic link library. This would communicate with database abstraction layer library using only datasets. Database abstraction layer library would communicate with SQL Server stored procedures. And these would manipulate database tables.

The task for the weekend is figuring out how to do the same in Ubuntu using C++ with various libraries and Postgres?

It was Rok Pintar who brought Linux to Slovenia. He published the very first article about it in the Programmer newspaper. And then one day in the early 90ties Rok was kind enough to copy 65 floppy discs for me so I could get to know it too. Coming from CP/M and DOS environments and using Windows 3.11 at the time; I was impressed. Technically Linux was far superior to Windows 3.11.

But frankly I did not know what to do with it. In addition first MSDN was published and many companies started seeking "nigl-nagl-neu" MFC or VB programmers. I was in my early twenties, proficient in Clipper, and eager to earn me some easy money. Or so I thought. So when Windows 95 came I decided to move to this exciting new platform.

Six months ago I got sick of the colorful Vista, the impossible new Microsoft Office user interface and the rest of the kitch. One weekend I decided to install Ubuntu Linux on my home machine to check its progress. And I still use it today.

In my opinion Ubuntu distribution is a solid, mature desktop system. It has everything an office workplace needs. It is not a complete Windows replacement because it lacks killer applications in specific areas, such as - Bloomberg in finance, AutoCAD in engineering, Adobe Premiere in movie post production, etc. But it is apropriate for most workplaces now.

Now it needs a push by its community. To attract new generation of techies we need publicly available knowledge in areas of IT system architecture and programming that is not available for this platform today.

For example, when I install Windows network there are books available to tell me about Windows AD domain as optimal solution for security. But when I install Ubuntu there are no sources to advice me about using NIS / NIS+, Kerberos and other solutions.

Googling these issues soon leads to information overkill. A newcomer is confused. He has all these technologies for creating small Ubuntu LAN available but yet he is not even able to create common network user names for workstation users and common folders.

Ubuntu programmers face similar troubles. Every child can pick a book and read about developing a three tiered business application for Windows using SQL Server and .NET. But there are no good resources about business application programming for Linux. While there is abundance of know-how about SQL Server, chained security,.NET, and web services; the situation is different for Ubuntu. We're pretty much on our own. It's easy to develop web service in .NET. There is only one way to do it. It's hard in Ubuntu and there are many different solutions; from creating your own server to using PHP.

Thus as I uncover the secrets of Unix business programming I will share them with you on this blog. I will write from the perspective of former C++/VB/.NET/SQL Server developer. I will develop a framework that will provide guidelines and best practices and enable rapid business application development to hobby programmers (like myself) and/or to professionals who might some day follow my path to the uncharted area of Ubuntu business application development.

At the end I promise to follow one very important rule. I will not publish "40 ways to establish a LAN domain in Linux" articles. I will only describe the best (and most Unix) way of doing it. And stick to it. This blog will be about solutions; not about choices.

If you are like me and are interested in developing for Unix, why don't you join me in writing this blog?