Success with C++

Having recently written on the possible decline of C++, it is perhaps only fair that I share a success story about C++. The C++ programming language is still alive, and still useful. I should know, because a recent project used C++, and successfully!

The project was to maintain and enhance an existing C++ program. The program was written by other programmers before I arrived, over a period of years. Most of the original developers were no longer on the project. (In other words, a legacy system.)

The program itself is small by today's standards, with less than 300,000 lines of source code. It also has an unusual design (by today's standards): The program calculates economic forecasts, using a set of input data. It has no interaction with the user; the calculations are made completely with nothing more than the input data and program logic.

We (the development team) have successfully maintained and enhanced this program by following some rules, and placing some constraints upon ourselves. The goal was to make the code easy to read, easy to debug, and easy to modify. We made some design decisions for performance, but only after our initial design was shown to be slow. These constraints, I think, were key to our success.

We use a subset of C++. The language is large and offers many capabilities; we pick those that are necessary. We use classes. We rarely use inheritance. Instead, we build classes from composition. Thus, we had no problems with slicing of objects. (Slicing is an effect that can occur in C++, when casting a derived class to a base class. It generally does not occur in other OOP languages.) There are a very small number of classes that use inheritance, and in those cases we often want slicing.

We use STL but not BOOST. The STL (the Standard Template Library) is enough for our needs, and we use only what we need: strings, vectors, maps, and an occasional algorithm.

We followed the Java convention for files, classes, class names, and function names. That is, each class is stored in its own file. (In C++, we have two files, for the header file and the source file.) The name of the file is the name of the class (with a ".h" or ".cpp" extension). The class name uses camel-case, with a capital letter at the beginning of each word, for names such as "Year" or "HitAdjustment". Function names use snake-case with all lower-case letters and underscores between words. This naming convention simplified a lot of our code. When creating objects, we could create an object of type Year and name it "year". (The older code using no naming conventions, and many classes had lower-case names, which meant that when creating an object of type "ymd" (for example) we had to pick a name like "my_ymd" and keep track mentally of what was a class name and what was a variable name.)

We do not use namespaces. That is, we do not "use std" or any other namespace. This forces us to specify the namespace for every class. While tedious, it provides the benefit that one can easily see the class for function names. There is no need to search through the code, or guess about a function.

We use operator overloading only for a few classes, and only when the operators are obvious. Most of our code uses function calls. This also reduces guesswork by developers.

We have no friend classes and no friend functions. (We could use them, but we don't need them.)

Our attitude towards memory management is casual. Current operating systems provide a 2 gigabyte space for our programs, and that is enough for our needs. (It has been so far.) We avoid pointers and dynamic allocation of memory. STL allocates memory for its objects, and we assume that it will manage that memory properly.

We do not use lambdas or closures. (We could use them, but we don't need them.)

We use spacing in our code to separate sections of code. We also use spacing to denote statements that are split across multiple lines. (A blank in front and a blank after.)

We use simple expressions. This increases the number of source lines, which eases debugging (we can see intermediate results). We let the C++ compiler optimize expressions for "release" builds.

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By using a subset of C++, and carefully picking which features make up that subset, we have successfully developed, deployed, and maintained a modest-sized C++ application.

These constraints are not traditionally considered part of the C++ language. We enforce them for our code. It provides us with a consistent style of code, and one that we find readable. New team members find that they can read and understand the code, which was one of our goals. We can quickly make changes, test them, and deploy them -- another goal.

These choices work for us, but we don't claim that they will work for other teams. You may have an application that has a different design, a different user interface, or a different set of computations, and it may require a different set of C++ code.

I don't say that you should use these constraints on your project. But I do say this: you may want to consider some constraints for your code style. We found that these constraints let us move forward, slowly at first and then rapidly.