C++ dlopen mini HOWTO. Aaron Isotton.. $Id: C++-dlopen- ,v /12/08 aisotton Exp $. C users will need to include the header file to use this API. dynamically loaded (DL) libraries should also consult the “C++ dlopen mini- HOWTO”. Shared Library Mini-Tutorial A shared library is a binary file that contains a set of callable C functions. Visit the dlopen man page for more information.

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Basically, my goal is to build a program which allows the user for modeling and simulation of arbitrarily composed physical systems, e. I assume to have a library of physical models functions within classes. Each function may have some inputs and return some outputs depending on the underlying physical description, e. Now, the idea is to provide the user a framework which allows him to compose any functions according to his needs, i.

The framework should provide functionalities to connect the outputs and inputs of different functions. Therefore, the framework provides a container class. These containers can also hold other components cf. Additionally, the component class provides some general numeric functionalities such as math solver and so on.

Shared Library Mini-Tutorial

The composition of functions should be done during runtime. In the first instance, the user should be able mihi-howto set up a composition through importing an XML which defines the composition structure.

Later, one could think of adding a GUI. It is not necessary to dive deeper into the framework’s capabilities because my problem is much more general. However, I am sure that the concept of “building objects during runtime” is very often required. What do I overlook? Three Easy Pieces for a good overview. Several modern operating systems allow dynamic loading of plugins.

Windows has something different LoadLibrary and an inferior linking model; you need to explicitly annotate the functions concerned, provided, or used by plugins. BTW on Linux you can practically dlopen a big lot of plugins see my manydl.

C++ dlopen mini HOWTO

So your XML thing could drive the loading of plugins. Because of it, you’ll better declare as extern “C” the functions related to plugins and defined in them, and accessed by dlsym from the main program. And libffi enables you to call functions whose signature is only known at runtime. Another possibility is to embed some interpreter, like Lua or Guilein your program or write moni-howto own one, like Emacs did.


This is a strong architectural design decision. Dllopen are variants or mixes of those approaches.

Shared Library Mini-Tutorial

You could use some JIT compilation library like libgccjit or asmjit. In all these approaches, memory management is a significant concern it is a “whole program” property, and what actually is the “envelope” of your program is “changing”. You’ll need at least some culture about garbage collection. Read the GC handbook for the terminology.

Read also about dynamic software updating. Notice that some programming languages, notably Common Lisp and Smalltalkare more friendly to the idea of runtime importing functions. SBCL is a free software implementation of Common Lisp, and compiles to machine code at every REPL interaction and is even able to garbage collect machine code, and can save an entire core image file which can be later easily restarted. At its most basic, you are looking for a graph-oriented data structure.

Your physical models are built up of nodes you call them componentsand edges connectors in your naming. There’s no language enforced mechanism to do this, not even with reflection, so instead you’ll have to create an API and any component that wants to play will have to implement several functions and abide by rules set forth by your API.

And that’s just for setting up your graph. You’ll need additional functions defined dlopne organize how your model is actually executed.

Each function mino-howto have a specific name and all components must have those functions. Anything specific to a component must be reachable through that API, in an identical manner from component to component.

Your program should not be trying to call these dlopfn defined functions’. Instead, it should be calling a general purpose ‘compute’ function or some such on each component, and the component itself takes care of calling that function, and transforming its input to its output.


The input and output connections are the abstractions to that function, that’s the only thing the program should see. With mini-howro function defined by the API, you’ll know what function names to call at runtime, and you’ll know the datatypes of each of those calls, and you just use regular old dynamic library loading to get it done. This will mini-uowto with a fair amount of boilerplate, but that’s just part of life.

By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies. Home Questions Tags Users Unanswered. Of course, I have used the search but have not found any directly linked answer. To give you a better understanding here is a very simplified example: Robert Andrzejuk 1 8. Are all the functions compiled into the executable, or are they in dynamic libraries on what platform?

You’re going to have to look at something platform-specific. To do so, you need to know how function calls work at the assembly level of your chosen platform. P Please think about why that isn’t good enough and update the question. It helps when the real requirements are clear. Each component will need to implement a set of functions to do stuff like: Get the name of the component or other details about it Get the number of how many inputs or outputs the component exposes Interrogate a component about a particular input our output Connect inputs and outputs together and others And that’s just for setting up your graph.

Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. Post Your Answer Discard By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.