Every programming language has its benefits and its drawbacks. Python, for example, provides a dynamic and clean environment for the developer, which boosts productivity by hiding much of the “dirty work”: memory management, type inference (duck typing, in this case), and more. Such benefits usually come at the cost of efficiency, which is something that other programming languages (such as C++) excel in.
The next logical step would then be a way to combine the benefits of such different programming languages in a single system. For instance, we could use C++ solely for the cpu-intensive parts, while the rest of the software could very well be written entirely in Python. The missing piece would then be a way to integrate the two. The common way of doing so is through SWIG, which is a tool that is able to wrap C++ to many different programming languages, Python included. Using SWIG right out of the box, we will be able to invoke C++ code directly from a Python interpreter. But what if we wanted to extend C++ classes in Python, making native C++ seamlessly call Python code?
Continue reading Python directing C++
Writing fairly straightforward C++ code, we usually make heavy use of the RAII concept. Therefore, we greatly rely on the simple (and basic) assumption that all appropriate destructors will be called. What happens if that is not the case?
Continue reading Unexpected skip of a destructor
Linux (through its dynamic linker) offers a mechanism for loading a predefined shared library prior to loading any other library. This feature can be utilized to override certain functions in other shared libraries (for instance, to ), or more generally: it can be used to get your own code to execute in the context of a different process. There are, of course, some security restrictions in place for preventing pre-loading your own code with setuid programs and the likes. In this post we shall present an exploitation of this feature which produces quite a frustrating prank.
Continue reading Preloading a segfault
A priority queue in the STL is nothing more than a regular (maximum-) heap. It is essentially an adapter built on top of another container, usually a vector. Therefore, the offered priority queue can easily contain an arbitrary number of elements (so long as memory permits).
But what if we wanted to keep only the biggest N elements, and just have the queue dynamically throw away all other elements? I am sure you can imagine why such a behavior would be much desired: for instance, keeping the best N suggestions for a specific search term springs to mind. Unfortunately, the STL does not support such an adapter.
Continue reading Bounded size priority queue
Generic programming is very common and has different names (and features) in various programming languages; C++ provides Turing-Complete Templates, Java offers Generics (along with Ada, Eiffel, C#, and Visual Basic .Net), and Parametric Polymorphism is present in ML, Scala, and Haskell.
While I am generally pretty happy with what C++ has to offer, adopting some of the features offered by other mechanisms can come in handy sometimes. To be more specific, in this post we will mimic Java’s support for defining a common super-type for generic elements (i.e. List).
Continue reading Imitation of Java Generics