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)
Related
I've looked over a few questions with a title just like this one, but they either do not talk about command line, or don't seem to work for me for some reason. From what I have read, it seemed as if I could "simply" do the following:
The dummy code (C#):
using System;
public static class Foo {
public static void Bar() {
Console.WriteLine("o3o");
}
}
More dummy code (Visual C++):
#using <test.dll>
int main() {
Foo::Bar();
return 0;
}
C# DLL compiled using:
csc /out:test.dll /t:library src\cs\Foo.cs
Visual C++ object file compiled using:
cl /Ox /clr /AI. /c src\vc\test.cpp
Executable compiled using:
link /out:test.exe test.obj
The following exception is thrown upon running the executable:
Unhandled Exception: System.TypeLoadException: Could not load type 'Foo' from assembly 'test, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'.
at main()
at mainCRTStartup()
I have a strong feeling that I was supposed to also reference the DLL in the link phase, but I couldn't find any option for linking a DLL similar to GCC's -l option. Attempting to pass the DLL along with the .obj to link causes it to tell me that linking assemblies is not supported. Interestingly, though, if I build a .netmodule instead of a DLL, i.e. by:
csc /out:test.dll /t:module src\cs\Foo.cs
and changing the #using directive to
#using <test.netmodule>
the executable runs without error. This feels a bit weird, for I don't think anybody packages code in .netmodules (what are .netmodules, anyway?).
All of your steps should have worked, but one very simple issue is preventing your program from running.
Namely: Your C# DLL assembly name is test, and your C++/CLI exe assembly has the same name. They both have the same identity.
So when looking for Foo::Bar in the test assembly, the loader first checks if the assembly is loaded in the AppDomain. It is - it's your C++/CLI exe, and you can't have several assemblies with the same identity loaded simultaneously within the same AppDomain. Your C# dll wasn't even given a try.
Just change either one of them and everything will work fine:
link /out:test2.exe test.obj
As for what's a .netmodule, it's the format used for linking managed code statically, that's why you managed to link your C# code with your C++/CLI code without issues. It's roughly the equivalent of a .lib file for managed code.
And you're right, it's not used very often.
I have a C++ dll compiled using VS2013.
I call it in my C# application like this :
[DllImport("myDLL.dll", EntryPoint = "RestartIfNecessary", CallingConvention = CallingConvention.Cdecl)]
public static extern bool RestartIfNecessary(uint uiAppId);
And it works fine.
However once the application is in prod some users have the following error :
Unable to load DLL 'myDLL.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
I can't find why this error happens on some computers. We've been able to fix the issue for some users by removing Microsoft Visual C++ 2013 Redistributable (x86) and (x64) and installing them again.
My C# application is compiled to run on x86.
I have a 64bits w10 and it works fine, so I don't know if it's related to windows.
Have you any hint to help me fixing this issue ?
EDIT: Here are the results of dependency walker :
In dependendy walker I've found 3 dll in red, I don't know if they are important:
API.dll is a third party dll (myDLL is a wrapper for this API)
The error means either myDLL.dll itself, or one of its dependent DLLs, cannot be found on the DLL search path.
Make sure myDLL.dll is placed where your app can find it. You can load myDLL.dll into Dependency Walker on the problematic computers to pinpoint any missing dependencies.
I have a program that uses Tesseract to extract text from images. I made a Native C++ DLL that is used in C# via P/Invoke. My C# application is a console x64 based and the DLL is also 64 bit.
After deploying to a Windows Server I receive an error that suggets the DLL (one I've made) does not exists. The error message is below.
System.DllNotFoundException: Unable to load DLL 'TesseractX64.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E) at Utilities.Finance.PDFParser.PDF.OCRObject.GetUTF8Text(String path, String lang, String imgPath)
I know for sure that the DLL exists in that path. The TesseractX64.DLL is placed in the same folder as the C# application so it should work without any issues.
Here is my code:
[HandleProcessCorruptedStateExceptions]
[DllImport(#"TesseractX64.dll", EntryPoint = "GetUTF8Text", CallingConvention = CallingConvention.Cdecl)]
private static extern IntPtr GetUTF8Text(string path, string lang, string imgPath);
What I have tried so far:
Set the DLLImport path to a relative path for example C:\DLL\Tesseract.DLL. Still same issue.
Installed Visual C++ 2005 - 2012 both x86 and x64. Still same issue.
It works perfectly fine on my Windows 7 x64 computer that I used to develop the program.
Either:
The DLL cannot be found, or
One of the DLL's dependencies cannot be found.
Place the DLL in the same directory as the executable to ensure that it can be found.
Make sure that all the DLL's dependencies are met on each machine that needs to run your software. That will involve first working out what those dependencies are. The documentation for the DLL should tell you that information. Typically this means installing the MSVC runtime against which the DLL was linked.
You aren't allowed to redistribute the debug runtime. You'll want to make a release build of the native DLL even if the .NET code is in debug mode.
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.