I have a managed dll file which imports functions from a C++ dll to the managed environment. I'm using some of its functions in my program but the problem is, I get this error when I use it:
Unable to load DLL 'Libraries\lib.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
I placed the .dll file in the program's directory and in the system32 folder. However, it still doesn't work. I think I have to use DLLImport but I have no idea how to use it.. even after looking at some examples I am still confused. Can someone help me here?
You say:
I placed the .dll file in the program's directory...
But:
Unable to load DLL 'Libraries\lib.dll'
We need to see your DLLImport attribute creation, i.e., the C# signature of the native method. It looks to me like you probably specify the path, i.e.,
[DllImport( "Libraries\lib.dll" )];
static extern void MyNativeMethod();
Try using this instead:
[DllImport( "lib.dll" )];
static extern void MyNativeMethod();
That will search the running directory as well as through your PATH environment variable. If you specify a file path as you do I honestly don't know if it will search through PATH if the file is not found (I couldn't find mention of it in the docs).
There isn't enough information here to help, as you're not showing the API (in native code) you're trying to import, etc.
That being said, I'd strongly recommend reading the Platform Invoke Tutorial as well as A Closer Look at Platform Invoke on MSDN. They walk through the main issues, as well as showing many examples of how to import and use functions from a C++ DLL.
The best and easiest way of using a c++ dll file in c# :-
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Runtime.InteropServices;
namespace demo1
{
class Program
{
[DllImport("shi.dll", EntryPoint = "?HelloWorld##YAXXZ")]
public static extern int HelloWorld();
public static void Main(string[] args)
{
//Console.WriteLine(StringUtilities.HelloWorld());
Console.WriteLine(HelloWorld());
// public static extern void HelloWorld();
// HelloWorld();
// Console.ReadKey();
}
}
}
If you are sure of the exports (use dependancy walker to check) and that you have correctly mapped them using the correct PInvoke calls, then your issue might be 32/64 bit related especially if you are on a 64bit OS with a .NET application set to Any CPU.
A 32 bit native DLL can only be loaded by a 32 bit .NET process when using PInvoke (the same applies to 64 bit native DLLs).
You can change the platform target using Properties->Build->Platform target or you can use the CorFlags utility.
I faced the same issue with different .dll file , the solution was to change the target to x64 instead of x86
Related
I am creating an Autodesk Revit add-in in C#. Output of this project is a DLL itself. Within this project, I am loading another unmanaged DLL by calling:
IntPtr pDll = LoadLibrary("E:\\Rep3DLib\\builds\\Release\\Index.dll");
int a = Marshal.GetLastWin32Error();
Within debugger, I see that pDll has value 0 and a has value 127 (Error: The specified procedure could not be found.). This is surprising because I am not even looking any particular procedure within the DLL. I just want to load the DLL.
Now I delete the unmanaged DLL from E:\\Rep3DLib\\builds\\Release\\Index.dll and in the above code, a has value 126 (Error: The specified module could not be found.). This does make sense. It also means that when the DLL is present at the correct location, the code is able to find it but somehow it's looking for a procedure which it's not able to find.
To debug this problem, I created another project within the same solution. Here's the code for this project:
namespace testIndex {
class Program {
[DllImport("kernel32.dll", SetLastError = true)]
public static extern IntPtr LoadLibrary(string dllToLoad);
static void Main(string[] args) {
IntPtr pDll = LoadLibrary("E:\\Rep3DLib\\builds\\Release\\Index.dll");
int a = Marshal.GetLastWin32Error();
}
}
}
When I run this, pDll has a non-zero value and I am able to call the functions defined within the Index.dll.
Note that both the projects have target platform as x64. I also verified that if I build the Revit add-in and run it on a different machine, it does find the DLL. So somehow it's not finding the DLL only on my machine although the path E:\\Rep3DLib\\builds\\Release\\Index.dll is definitely correct.
Any idea what could be wrong?
Here's the answer to the question I posted above. My add-in was using a dependent DLL named "pcl_features_release.dll". Revit was loading another add-in before mine, which was also loading its own "pcl_features_release.dll" which might be slightly different than mine. As a result, although Revit was finding my DLL, it was not able to load it.
Another question: In this case, two add-ins are dependent on "pcl_features_release.dll", which is a DLL supplied by Point Cloud Library (http://pointclouds.org/). What is the best practice to avoid conflict in such cases. I can not change someone else's add-in. How do I make sure that my add-in loads my "pcl_features_release.dll" that is being supplied with the add-in?
I want to use C++ code in a C# application, so I wrote a DLL in C++.
Because it's the first time that I create a C++ DLL, I started by creating a 'test' dll. Here's the code
extern "C"
{
__declspec(dllexport) void DisplayHelloFromDLL()
{
printf("Hello from DLL !\n");
}
}
Than I made a very simple C# application:
class DllTest {
[DllImport("Test.dll")]
public static extern void DisplayHelloFromDLL();
public static void UseDll() {
DisplayHelloFromDLL();
}
}
After, I built both applications and moved the executable and the dll in the same folder. But when I ran the executable, it showed the following message:
Unhandled exception: System.DllNotFoundException: Unable to load DLL 'Test.dll': The specified module could not be found
you need to store the DLL in debug folder.
and try this command to check that method is exported properly
dumpbin /exports Test.dll
you have to check the target platform of both dll and exe.
Edit: When Target are different the exception is BadImageFormatException
You will have the DllNotFoundException when the dll or one of its dependencies is not found.
For example, when you compile a debug version of the DLL with VisualStudio, it needs the debug runtimes (which are not installed on machine without the IDE).
you can check your dll dependencies using the Dependency Walker
This tools will also helps you to see the targetted system (x86/x64) and the exported functions (use it on the dll, the program will not show you the [DllImport] dependencies)
I'm calling the following from c#:
[DllImport("u3dapi10.dll", CharSet=CharSet.Auto)]
public static extern uint dapiCreateSession(out uint hSession);
Where is .NET looking for the u3dapi10.dll file? This was working previously but now I'm getting a DLLNotFoundException.
The u3dapi10.dll file is in the root directory of the project. I tried copying it to the bin/debug directory just to see what happens, but it couldn't find it there either.
Possible cause:
Could this be caused by the u3dapi10.dll not being 64-bit compatible? e.g. Is a DllNotFoundException thrown if you try to access a 32-bit dll from a 64-bit machine? Or would it throw a BadImageFormatException as suggested by BadImageFormatException when loading 32 bit DLL, target is x86
See: Specify the search path for DllImport in .NET
and
http://msdn.microsoft.com/en-us/library/ms682586%28VS.85%29.aspx
How do I call functions from a C++ DLL?
The C++ DLL contains functions like this:
__declspec(dllexport) bool Setup () { return simulation.Setup (); }
The C# program does this:
[DllImport("mydll.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool Setup();
The C# program crashes with the following message when it tries to load (?) the DLL:
An unhandled exception of type 'System.BadImageFormatException' occurred in TestFrame.exe
Additional information: There was an attempt to load a file with a wrong format (exception from HRESULT: 0x8007000B)
The C++ DLL is a standard DLL (no MFC, no ATL).
This error occurs when you try to load a 32-bit DLL into a 64-bit process. (Or vice-versa)
Until VS2010, C# projects are target any CPU by default and will run as 64-bit on a 64-bit OS.
You need to go to the Build tab in Project Properties and set the C# project to x86 only.
Is it possible that your exe and dll have different bitness (i.e. one is 64 and the other 32)?
Have you tried compiling the code for x86 platform?
See this blogpost for instructions.
It may not be appropriate for you to set the CPU architecture (platform target) for the assembly, but instead you can specify an alternate path to find the correct DLL to load.
How to use the correct unmanaged DLL file according CPU architecture? (32 / 64 bits)
I have an unmanaged C++ MFC dll that was developed in VS 6.0. I would like to use it in my C# app. I'm trying to use PInvoke.
Here is the C++ code:
// testDll.cpp : Defines the entry point for the DLL application.
//
#include "stdafx.h"
extern "C" {
BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
return TRUE;
}
__declspec(dllexport) int test(int a)
{
return a * a;
}
}
And here is how I'm trying to invoke the method "test" from C#:
// PInvokeTest.cs
using System;
using System.Runtime.InteropServices;
class PlatformInvokeTest
{
[DllImport("TestDll.dll")]
internal static extern int test(int number);
public static void Main()
{
Console.WriteLine(test(5));
}
}
This approach works just fine when I set C++ dll to be just a regular Win32 dll.
But once I change the project type to MFC ("Use MFC in a Shared DLL") I'm getting this error:
Unhandled Exception: System.DllNotFoundException: Unable to load DLL 'TestDll.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
at PlatformInvokeTest.test(Int32 number)
Thanks!
TestDll.dll probably can't load one of it's dependent DLL's.
Try loading your TestDll.dll file in the Depends (Dependency Walker) utility. Depends should be installed with VC 6, under Microsoft Visual Studio 6.0 Tools. That will show you what dependencies the DLL has and will flag if one of the dependencies failed.
Make sure you load the TestDll.dll from the same folder that the C# code does.
Note that Depends only works with unmanaged DLL's.
The DLL needs to be in a path where the system can pick it up. have you put it in the directory where your application starts ? (probably in a DEBUG folder of you VS solution).
The second option is to give it the absolute path of the DLL.
The third option is to place it in "c:\windows\System" but this is a '-1' approach :D
In general, when you hit errors like this you can use Assembly Binding Log Viewer to determine if the dll is failing to load because of a missing dependency.
In your particular case, the most probabl cause is that you are dynamically linking your dll to MFC and when the C# app attempts to load your dll, it is failing to load the MFC dlls.
You can either copy the required MFC dlls side-by-side or you can switch to statically linking MFC to your lib.