I am creating a COM library with Embarcadero C++ Builder. The designer for the ridl file gives several things you can add to the ridl. I think I understand all of them except for creating new "Modules". I can't find good information for it in the documentation.
What is a "Module" and what would it be used for in COM?
You say you can't find 'good information' in the documentation; what have you found? The RAD Studio help has a section specifically explaining modules, which says:
A module defines a group of functions,
typically a set of DLL entry points.
You define a module by
Specifying a DLL that it represents on the attributes page.
Adding methods and constants using the toolbar or the object list pane
context menu. For each method or
constant, you must then define its
attributes by selecting the it in the
object list pane and setting the
values on the Attributes page.
For module methods, you must assign a
name and DLL entry point using the
attributes page. Declare the
function's parameters and return type
using the parameters page.
For module constants, use the
Attributes page to specify a name,
type, and value.
Note: The Type Library Editor does not generate any declarations or
implementation related to a module.
The specified DLL must be created as a
separate project.
It seems it's specifying methods that exist in an external DLL to whatever module (EXE or DLL) the type library is built into. Exactly what that's used for... is a good question.
The module attribute is described in this MSDN Library page. It permits declaring entrypoints in a DLL. That has little to do with COM, it is just a capability of a type library. You'll find few language development environments that can use them. I think VB6 was one of them. Ymmv.
Related
I'm creating an application in VBA that uses a reference from vbscript.dll
I'm trying to figure out the best way to load the library, and am having difficulty distinguishing between using a declare function (http://msdn.microsoft.com/en-us/library/aa716201(v=vs.60).aspx) or just dynamically adding it to the list of references (How to add a reference programmatically, part 2 of the top answer)
If anyone can clarify the difference in result between the two, and maybe some advantages of one, I would be very happy.
My Notes:
I like the looks of a simple declare function, for one thing it's short and looks nice. For another, I like avoiding hard coded paths unless I know the files won't be found in different places.
On the other hand, I really like the error handling in method 2.
Declare is (typically) used for calling stdcall-supported functions exported from Windows DLLs. The VB run-time takes care of calling LoadLibrary, GetProcAddress, etc. to locate and load the functions you've declared. Most of the Windows API is used this way from VB/VBA.
References are used for COM objects -- that is, libraries that define a type library and a COM interface.
It's rare for a library to support both. If what you have is a COM library (if it appears in the 'References' dialog), add a reference to it and instantiate it that way.
i have a compiled dll library but i have no documentation about it. There is a way to get the public interface of a dll (at least function names, params numbers and type).
Thanks
You would have to decompile it and analyze each function, its calling convention, parametrs count, parameters meaning (unless it comes with some PDB, but I doubt it), I've done something like this before, it's complicated work, but it can be done.
In order to retrieve the public symbols (functions and variables) exported by a Dynamic-Link Library, one can use the well-known dependency walker. Parameters and Types are only available when the associated PDB file is available (which does not seems to be your case).
You could use the OLEViewer that comes with Visual Studio to view the TypeLib of the DLL if it is a COM library. This would give you the information you need.
I was convinced that there is no way to find COM dependencies of an ActiveX but to my surprise OLEVIEW shows some comments Like:
// TLib : // TLib : OLE Automation : {00020430-0000-0000-C000-000000000046}
importlib("stdole2.tlb");
// TLib : Visual Basic runtime objects and procedures : {EA544A21-C82D-11D1-A3E4-00A0C90AEA82}
importlib("3");
I tried to extract the same information using TypeLibInfoFromFile but based on what I find in MSDN, there is no Api that provides this information. Are you aware of a method to extract this information from OCX or it's Tlb file? Knowing that all my ocxes are compiled with vb6 can I trust this informaion for Imported(Explicitly not in code) interfaces?
Well, I've found the answer to this question. I'll write it here just in case someone would search for the same question. It's possible to find some of dependencies but you can never be sure if you have found them all. Basically you must enumerate every type and interface, and every member of each type to find all types in the module and for every type you find you should check to see if it's in an external TypeLib. in the end you have a List of Typelibs referenced.
The problem with this method lays in the fact you find only the types that are used in the public interface (fields, return values and parameters) and you miss every local object or dynamically created ones. That said you can check this link for an implementation or better yet this one.
It can be used to run arbitary Dynamic Link Library in windows,
how can it possibly know the entry point of an arbitary dll?
The answer depends on how much details you need. Basically, it comes down to this:
A DLL can optionally specify an entry-point function. If present, the system calls the entry-point function whenever a process or thread loads or unloads the DLL.
[...] If you are providing your own entry-point, see the DllMain function. The name DllMain is a placeholder for a user-defined function. You must specify the actual name you use when you build your DLL.
(Taken from the MSDN article Dynamic-Link Library Entry-Point Function.)
So basically, the entry point can be specified inside the DLL, and the operating system's DLL loader knows how to look this up.
The IMAGE_OPTIONAL_HEADER (part of the portable executable's header on Windows machines) contains an RVA of the AddressOfEntryPoint that is called by programs looking for an entry point to call (e.g., the loader).
More information on the IMAGE_OPTIONAL_HEADER can be found here. And this paper is good for just general PE knowledge.
What do you mean by "run a DLL"? DLLs aren't normal programs, they are just a collection of functions. The entry point itself usually doesn't do much apart from initializing stuff required by other functions in the DLL. The entry point is automatically called when the DLL is loaded (you can use LoadLibrary to do this).
If you want to call a specific function after loading the DLL, you can use GetProcAddress to get a pointer to the function you want.
First off , I'm referring to a Windows environment and VC++ compiler.
What I want to be able to do is rebuild a Vc++ dll and maintain compatability with an exe that has already been linked to the lib without having to rebuild the exe or load the dll dynamically using LoadLibrary. In other words, is there a way to add classes and methods to a dll(but not remove any) and ensure the existing entrypoints remain the same?
If you export the functions from using a DEF file and manually specify the ordinals, you should be able to accomplish this.
Reference
http://msdn.microsoft.com/en-us/library/d91k01sh(VS.80).aspx
It depends on how your EXE used the classes from the DLL. Adding new classes should not affect existing entrypoints. Aside from that, however, any the following will affect object size and/or layout, and as such will be a client-breaking change (note that this is technically VC-specific, but most of these apply to any sane implementation):
Removing fields (even private) from classes
Adding new fields (even private) to classes
Adding new base classes to existing classes
Removing base classes from existing classes
Adding new virtual method before an existing virtual method (adding new virtual methods after existing ones is okay, except for the case described in next point)
Adding a new virtual method in a class that is used as base class by another class in the same DLL which also has virtual methods
Changing type of existing fields
Changing signature of existing methods
Making a virtual method non-virtual, and vice versa
As long as you don't add any exported symbols, the ordinals won't change. If you add exported symbols through the standard dllexport mechanism, then that's going to be difficult to control. If you use the old style .xpf symbol file you might be able to control the ordering of the symbols in the lib (although I don't know this for sure - it might still reorder them however it likes), but it's tricky to do C++ symbols this way.
I think that ordinals are rarely used to resolve DLL imports anymore - I think that you have to use .def files to get the linker to use them. So as long as you don't change names or signatures of the exported functions, the .exe should work just fine.