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Hi all...
I'm new to c++ programming, and I wanna learn some programming concepts..
What I need is some tutorial or some directions on creating a program that accept modules, like apache, that accept the php module for example...
Does you know some books??
Thx...
you have to crawl before you can fly. what you're talking about is far in the distance from just starting out.
Yes, you should start off with something smaller, like most beginners that post here - a MMORPG. ;)
hehe thanks... I will do that...
The thing is that I'm not new to programming, i have programmed in java and c#, and in c# we do this with dependency injection with the cab framework. But my c# programming days are over...
Is there some framework for dependency injection in c++??
Thx...
I'm not entirely sure what "dependency injection" actually means.
Accepting modules, however, can be done in several ways. The easiest is probably to have a shared library that you load at runtime rather than directly link against the library. That way, you can decide which module(s) to load. If all modules have the same interface (or a subset of a standard interface), then you can use any of the modules interchangably, and get different behaviour from it.
Having said that, you do need a fair bit of programming experience and a bit of interface design experience to get there.
--
Mats
Yeah, I think of that.. Have an interface that all modules must implement.. The case is how can I load a module at run time??
I think of have a configuration file that tells me what modules to load with their options, but I dont know how to load a library at runtime...
Depends on the OS you are using. LoadLibrary works for Winodws, dlopen() is used for Linux and several other Unix flavours. Other OS's may or may not have a similar thing - if they don't, then the problem becomes a fair bit harder, because you basically have to achieve the same thing yourself.
--
Mats
[edit] Way too late for this reply. That's what happens when you leave tabs open indefinitely . . . . [/edit]
Unfortunately, loading other libraries or "modules" at runtime is platform-specific. I'm not sure how to do it on Windows, but I'm sure it's related to DLLs (which are runtime libraries under Windows). Under linux you'd probably use dlopen() and friends.
But really, this is quite complicated to do. I wouldn't recommend it unless you have a pretty good understanding of C++ already.
I'll program in linux...
Is there other ways of creating modules different of that???
There is no EASIER way to get external code into your project, but there may be ways to get flexibility without using external code.Quote:
Originally Posted by rluceac
It depends a lot on what you are trying to do. You may for example choose to have a little language of your own or configuration files that contain values/controls that allow you to do some flexibility in your application, rather than using externally generated code in a shared library or similar.
--
Mats
What I need is to let my app accept plugins, like firefox or so...
Ok, so what are you ACTUALLY trying to do?Quote:
Originally Posted by rluceac
Right now, I feel like the car-mechanic being asked "How do I undo a wheel-nut", when I know that no sane person wants to just undo a wheel-nut, it doesn't make any sense. So the customer PROBABLY has a puncture, and will be back in half an hour with another question. If you tell us what the ACTUAL problem is ("I've got a puncture, how do I fix it?"), then we can probably help a whole lot better than what you are describing so far.
Note that firefox plug-ins are written in JavaScript, so are not compiled in the same way that C or C++ code would be.
--
Mats
I disagree that this is all that complicated. On either Linux or Windows it comes down to opening a dynamic library then getting a pointer to a function within that library.
Linux:
Windows:Code:void *handle = dlopen("module.so", RTLD_LAZY);
void (*func)() = (void (*)())dlsym(handle, "fooFunc");
func();
Code:HMODULE handle = LoadLibrary("module.dll");
void (*func)() = (void (*)())GetProcAddress(handle, "fooFunc");
func();
Yes, I guess as long as function pointers are understood (at least at a basic level), then it shouldn't be that bad.
--
Mats
Humm... that's it...
I create interfaces to the functions the modules must implement, configure the modules to be load in an text file or XML file, and then load the with dlopen...
Thanks a lot...
Because this is C++, there are a few things to consider... The names of C++ functions are mangled, which makes it hard to use dlsym(). You have to mangle the name the exact same way the compiler did, and that's not always easy.Quote:
Originally Posted by rluceac
Thus, public functions in loadable C++ modules are often declared extern "C" to cause them not to be name-mangled. A module for a C++ architecture might provide one or two entry points which are basically factory calls that instantiate module objects.
Suppose that every module inherits from this class:
Then a module which implements a "FooModule" might look like this:Code:class MyModule
{
public:
virtual ~MyModule() {}
virtual void DoIt() = 0;
};
The main program might load the module like this:Code:class FooModule : public MyModule
{
public:
void DoIt()
{
// implement the module code
}
};
extern "C"
MyModule *CreateModule()
{
return new FooModule();
}
Unloading modules can be tricky, because you can't unload safely unless all object instances from that module are destroyed. You could use some kind of reference counting, or punt the issue and just never unload a module once it has been loaded.Code:// Load the module
void *handle = dlopen("FooModule.so", RTLD_LAZY);
// Get the factory
MyModule *(*factory)() = (MyModule *(*)())dlsym(handle, "CreateModule");
// Create the object
MyModule *module = factory();
// Do it!
module->DoIt();