In my windows application i have to load a dll dynamically. I achived this by DllImport attribute. But when i execute the command in Developer Command Prompt for Visual Studio dumpbin /exports on a DLL only 5 functions listed. I can't see my required function .But i can aceess the method when static linking. Is there any way to access the required function dynamically.
You can only call functions in a DLL that are exported. If this is your DLL then you need to recompile it to export the functions that you need to call. If it is not your DLL, and the function is not exported, then you are out of luck.
You state in comments that the function can be called when you link to the DLL statically. That means that the function is exported. Its name is likely mangled or decorated so that you do not recognise it. Once you can work out what the mangled or decorated name is, you will be able to link to the function with runtime linking.
Another possibility is that the function is exported from a different DLL, or perhaps even defined in a static lib. Without more details we cannot give you anything much more definitive than this.
Related
I've been provided a DLL that has been written in C++. Along with the DLL I receive the required input parms and expected output as well as a .h include file.
Can't seem to get it included as a Reference in my project. My procedure is to right click References and Add Reference, click Browse and then double click on the DLL. The error I get is:
A reference to 'c:......\dll' could not be added. Please make sure
that the file is accessible, and that it is a valid assembly or COM
component.
The problem is likely due to the name mangling of C++, but I'm not sure how to overcome the problem. I've been told by the author of the DLL that it was written for another customer who ran into the same issue, but was eventually successful in getting it referenced. I don't have access to that 'customer' and was wondering if anyone had suggestions.
Adding a reference is not how you link to this unmanaged DLL from your C# code. Instead you need to either:
Translate the header file to C# p/invoke calls, or
Create a C++/CLI wrapper around the unmanaged DLL and add a reference to that from your C# project. This option would typically involve linking to the .lib import library for the DLL which should be supplied with the DLL.
I made an application in vs2010 (.net 4.0). I published it, both using publisher and InstallShield LE.
But when I run application, I get error that a dll is not found. I know which dll is missing. This is a non-COM object and I can't add it to my project in vs2010. I am using a wrapper library which invokes this dll.
If I paste that dll in syswow64, my application works fine. But I want a cleaner way of doing it. I already had a look at Hans's answer here. But I have no clue what is side-by-side cache.
Adding path to environment variables works fine too.
I am not sure if updating registry and adding a path value will work or not. I would like to know if I can update registry for my application and direct the path where it searches for particular dlls.
Thanks.
Modifying the user's PATH variable is a very heavyweight solution, and you should avoid that. Likewise, do not put the DLL in the system directory. That belongs to the system and is private to you.
The recommended way to solve the problem is simply to put the DLL in the same directory as the executable. The directory in which the executable lives is searched first when the loaded tries to locate DLLs. It is the safest place to put your native DLLs.
If for some reason you cannot put the DLL in the executable directory, there are other options:
Call SetDllDirectory with the directory of your DLL before making your first p/invoke call. When that call returns, call SetDllDirectory passing NULL to restore the default DLL search order.
Make an explicit call to LoadLibrary with the full path of your DLL before making your first p/invoke call. Once the DLL has been loaded, future p/invoke calls will use the module that has been loaded.
If you know the DLL name in advance, there is a simple way.
You can simply use LoadLibrary to load the DLL from its known location (based on for example a configuration file entry).
As long as you successfully call LoadLibrary before any of the DLL methods are used, this will succeed as the DLL is already loaded.
This works because you can LoadLibrary with a full path, and once that is done, subsequent calls to LoadLibrary with just the filename will succeed immediately, since the library is already loaded.
I'm working on a C# component which consists of two DLLs:
A .DLL written in C++/CLI exporting a symbol; unfortunately, this DLL dynamically links against the CRT and there doesn't seem to be a way around that.
A C# assembly.
The C++/CLI DLL gets loaded and then loads the C# assembly (and forwards most calls to it). Is it possibly to simplify this scenario so that I export a symbol from the C# assembly right away?
You can export your functionallity from C# as a COM server this way it should be pretty easy to call it from C++ as you would do with any other non-C# COM object.
I ended up going for the solution described in http://www.codeproject.com/Articles/37675/Simple-Method-of-DLL-Export-without-C-CLI
The general approach is to have a dedicated attribute which is used to decorate the functions to be exported. After building the assembly, ildasm is used to disassemble it. The resulting IL is patch a little bit so that the previsouly decorated functions are exported, then the IL is assembled into an assembly again.
I've been given a dll to talk to a device, I have little to no experience in C# and I'm supposed to get the device initialized by the end of the week. The dll has methods to open ports and send messages, but I have no idea how to get access to the functions
I know its a bit ridiculous to ask but im running out of time.
Thanks,
Add a Reference to the .dll file in your C# project.
Add a Using namespace at the top of whatever class is going to interact with the .dll methods.
You will now be able to access the methods.
Edit: If your library is unmanaged you'll have to use Pinvoke.
Generally speaking, a feature to call from managed code into unmanaged code (which I assume your DLL is) is called P/Invoke and generally involves annotating required static extern methods with attributes.
Add a reference to the dll in your project (selet browse to find it) and you should be able to access the functions within. As for how to make your device work with it, I think you're on your own :)
If the DLL is a .Net assembly, you can load it into a Visual Studio project by adding it as a reference.
In the absence of documentation, it can also be extremely helpful to load the assembly into .Net Reflector, which lets you inspect the guts of the assembly, even to the point of disassembling the code inside the methods.
1- If it is managed Dll , i.e. Written using .net framework than calling a method from the dll is like you are calling a method from your own class.
just add the reference of the dll in your project and include the namespace reference by 'Using' keyword.
2- If it is not than you need to import your dll dynamically, you can use [DllImport]
I'm trying to use the lame_enc.dll file from LAME in a C# project, but adding the thing seems impossible.
I keep getting an error that says that a reference could not be added and to please check if the is accessible, a valid assembly or COM component.
I have no C++ experience, though I would like to use the functionality. Right now I'm using Process from the .NET framework to call lame.exe and do stuff, but I'd like to know if there's another way.
You can only add managed assemblies as a reference to a managed project. What I normally do in this situation is to add it as ressource instead with "copy local" settings. That way the DLL is tied to and deployed with your project. I then use DllImport to manually get the APIs I need from that DLL.
You have to use P/Invoke to call unmanaged APIs from managed code.
To use an unmanaged dll (native C++) in C#, you have to use DllImport, not adding a reference to the project in visual studio (and that is why you get an error).
Here is the documentation of DllImport from the MSDN.
You will need to use PInvoke to call functions in your native lame dll. However, you will only be able to call functions that have been exported as "C" style.
You can use a tool like "PInvoke Interop Assistant" that will help you when working out the PInvoke call signatures to make calls from C# to your native dll:
http://clrinterop.codeplex.com/releases/view/14120