I need to import a function that I wrote in C++, and is now compiled into a DLL, into my C# application. Everything builds without errors or warnings, but when I step through the code the first function call into the DLL throws an Exception with a message of "Unable to find an entry point named 'CreateScanEngine" in DLL 'WMIQuery.dll'." The function is declared like so in my C# application:
internal static class WMIQuery
{
[DllImport("WMIQuery.dll", CallingConvention = System.Runtime.InteropServices.CallingConvention.StdCall)]
internal static extern void CreateScanEngine();
}
Dependency Walker shows the function there in the DLL as such:
Ordinal: 1(0x0001)
Hint: 0(0x0000)
Function ^: void CreateScanEngine(void)
Entry Point: 0x00001860
Dependency Walker also shows these errors/warnings for the DLL:
Error: At least one required implicit or forwarded dependency was not found.
Warning: At least one delay-load dependency module was not found.
Warning: At least one module has an unresolved import due to a missing export function in a delay-load dependent module.
Will this make a difference? Also, I tried adding the DLL as a reference to the C# project, and I got this error:
A reference to [my DLL] could not be added. Please make sure that the file is accessible, and that it is a valid assembly or COM component.
Does anyone know what I'm doing wrong? Thanks.
Don't use Dependency Walker, it unmangles the exported name of the function and doesn't tell you the real export name. Note that it is smart enough to see that it takes no arguments and has no return value. It can only do this if it sees the name as decorated by the C++ compiler.
Use Dumpbin.exe /exports on the DLL to see the real name. It ought to be "?CreateScanEngine##YGXXZ", use the EntryPoint property in the [DllImport] attribute. You may also want to declare the function with extern "C" so this name mangling doesn't happen.
How are you declaring CreateScanEngine in your C++ code?
Try changing to:
extern "C" __declspec(dllexport) void __stdcall CreateScanEngine();
Related
I'm trying to import a C++ Project Dll into a C# project. I found a lot of people talk about using DllImport. I tried using that and here is what I have-
CPP Code:
int __declspec(dllexport) beginCode(double reportId);
C# Code:
[DllImport("C:\\Users\\<my_user_id>\\Desktop\\ctxmix\\Release\\ctxmix.dll",CallingConvention =CallingConvention.Cdecl ,CharSet = CharSet.Ansi, SetLastError = true, ExactSpelling = true)]
public static extern int beginCode(double reportId);
int result = beginCode(reportId);
But when I run, I'm getting an exception - Exception thrown:
System.DllNotFoundException
Do I have to add any references for the CPP Dll in the project or do anything else apart from the code which I have on the top?
Edit: I'm trying to run my .exe using VS2015 and I get this exception on my local machine. Also, I don't see my CPP Dll in the Project->References section where as I see other references there.
The unmanaged DLL needs to be locateable by your managed process. Typically that means placing the DLL in the same directory as the executable file. But you gave used an absolute path which I presume you transcribed correctly.
You may also encounter this error if the DLL's dependencies cannot be located. That seems the likely explanation here. Most likely the MSVC runtime cannot be located when your DLL is loaded.
Using an absolute path isn't a great idea. That will break down when you distribute to another machine. Use just the DLL file name and place it in the same directory as the executable.
Your DllImport attribute seems fussy. No point specifying CharSet when there is no text. I doubt your function calls SetLastError. And do you really need ExactSpelling?
I have a C# project which is a library I reference in one of my C# tests I have:
myproj
|-bin
+-External
| |-pHash.dll
|-main.cs
|-MyClass.cs
|-myproj.csproj
pHash.dll is a Visual C++ library (compiled using a vcproj project, so we are talking about Microsoft C++ flavor) called phash which exposes this method:
int ph_dct_imagehash(const char* file, ulong64& hash);
I want to use this method from MyClass.cs. So I do this:
public class MyClass {
[DllImport("pHash.dll")]
static extern int ph_dct_imagehash(
[MarshalAs(UnmanagedType.LPStr)] string file,
[MarshalAs(UnmanagedType.U8)] UInt64 hash);
public MyClass() {...}
public DoStuff() {
UInt64 outputValue = 0;
ph_dct_imagehash("a string", outputValue); // The second parameter should be a pointer in the C++ implementation, not really sure if I am doing it right here
}
}
In my project, I set External/pHash.dll to be Content and also set it to be Always copy in the output folder.
A possible mistake As I pointed out, the way I use ph_dct_imagehash might be wrong, but this question is about a different error I get, so please skip this and move on :)
MyClass is then referenced in one of my tests I execute using MSText.exe.
The error
When I try to run my test which is using that class I get:
System.DllNotFoundException: Unable to load DLL 'pHash.dll': The
specified module could not be found. (Exception from HRESULT:
0x8007007E)
What am I doing wrong?
Second attempt
I saw that, when building, actually my bin folder looks like this:
myproj
+-bin
|-External
|-pHash.dll
So I thought I had to change the path to the DLL:
public class MyClass {
[DllImport("External/pHash.dll")]
static extern int ph_dct_imagehash([MarshalAs(UnmanagedType.LPStr)] string file, [MarshalAs(UnmanagedType.U8)] UInt64 hash);
...
}
But then I get:
System.DllNotFoundException: Unable to load DLL 'External/pHash.dll': The
specified module could not be found. (Exception from HRESULT:
0x8007007E)
Another question
Is there a (maybe debugging?) tool to understand what path is the CLR trying to follow when encountering DllImport? So at least I know where it is trying to look for that dll...
More info
I have been asked to inspect my dll, so by using DependencyWalker on pHash.dll, I get this error:
Error: The Side-by-Side configuration information for
"c:\myuser\testresults\myuser-0131
2016-05-06 08_56_50\out\PHASH.DLL" contains errors. The application
has failed to start because its side-by-side configuration is
incorrect. Please see the application event log or use the
command-line sxstrace.exe tool for more detail (14001). Error: At
least one required implicit or forwarded dependency was not found.
Error: At least one module has an unresolved import due to a missing
export function in an implicitly dependent module. Error: Modules with
different CPU types were found. Warning: At least one delay-load
dependency module was not found. Warning: At least one module has an
unresolved import due to a missing export function in a delay-load
dependent module.
This error is also reported in the stack trace when I run my test. I thought it was a message coming from MSTest about something else, but now I realize it is a problem of this DLL!
Even if your DLL is found (sits in the test directory), it is still reported as missing when some of it's dependencies are not found. Make sure you copy the DLL itself and all DLLs it depends on.
You can set select your dll in Solution Explorer, right click on it and set BuildAction to Content and Copy To Output directory to CopyAlways. That way your dll will be copied to application directory and DllImport should find it.
Alternatively, use DllImport's SetDllDirectory with DLL path before first call of your imported dll
[DllImport("kernel32.dll")]
static extern bool SetDllDirectory(string yourPath);
I have a Lua module (lpack) that I need to load into LuaInterface. I've tried a few different configurations for the project, but I can't seem to figure out the linking.
I get the error unresolved external symbol "void __stdcall lua_replace(struct lua_State *,int)" (?lua_replace##YGXPAUlua_State##H#Z) referenced in function "int __stdcall l_unpack(struct lua_State *)" (?l_unpack##YGHPAUlua_State###Z)
If I run dumpbin /exports on the lua51.lib file, I can find ?lua_replace##YAXPAUlua_State##H#Z which matches what I find in the lua51.dll with Dependency Walker ?lua_replace##YAXPAUlua_State##H#Z, so the function exists but the names don't match.
I'm not very familiar with this level of linker management, so this may be a simple error on my part. Why is the value in the lpack build not matching that of the lua51.lib input file?
Update
All of the exports in the lua51.dll and lua51.lib files were __cdecl and my lpack project has been set to __stdcall. Changing that property (under C/C++ -> Advanced -> Calling Convention) fixed the compile issue and I now have an lpack.dll file.
However, when I attempt to load the file from lua require('lpack') it fails with The specified procedure could not be found.
Breaking in the lua C code that loads the library with LoadLibraryA returns NULL and a GetLastError() code of 0x7F.
Update 2
The lpack.dll file I was attempting to load was out of date due to a wrong output directory, so that fixed the LoadLibrary failure. Next the GetProcAddress would fail, but if I added extern "C" to the export function in the lpack.c file as per Mud's recommendation, the problem was resolved.
However, when I attempt to load the file from lua require('lpack') it fails with The specified procedure could not be found.
Probably because the name is mangled. Did you look in the DLL to see the actual (mangled) name of the function?
You really ought to build the Lua source (and any Lua modules written in C) as C, and use extern "C" when importing them. Save you a lot of headaches.
I got a DLL that I want to add to my C# project and I have some problems. First, my DLL is coded in C++ and I got an interface of one function to export it.
extern "C" __declspec(dllexport) char* sniff()
{
return ps.Sniff();
}
I have an instance "ps" that initialise a socket when the DLL is attached. The point is that I need to have this instance initialise when I call my exported function. My problem is when I import it in my C# project, my DLL is detached for no apparent reason and I can no longer call my exported function.
I use this syntax in my C# projet :
[DllImport(#"C:\Documents and Settings\Pat\Bureau\sniffoporn\Release\sniff.dll", EntryPoint = "sniff", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]
public static extern IntPtr sniff();
Some important things that I tryed :
Import the DLL in the reference of the project : Can't because it's not a COM component.
Manually import the DLL using LoadLibrary, FreeLibrary and GetProcAddress : Same result
Call my exported function in loop : Same thing but the DLL is attached for a little longer before detaching.
I would want to know why my DLL is detaching and how can I keep it attached for the rest of the process life.
Thanks a lot
Maybe an exception occurs in your DLL itself. Making it detach in Visual Studio to prevent your application from crashing. After all C# is managed code.
Try your same procedures with a different (dummy) dll with very simple functionality. If it still occurs then something with your method is wrong, otherwise with the DLL you are attempting to use.
I have a C# winapp. I call a native .dll file (created in C++ by myself) from the C# app, and it works fine.
But when I copy my application (.exe and .dll files) to another machine, I get an error that says:
Unable to load DLL "c:\dllname.dll": The specified module could not be found. (Exception from HRESULT: 0x8007007E)
Here is the C# code:
class IsoMessageHelper
{
public const string ISO8583_DLL = "c:\\Hc8583.dll";
[DllImport(ISO8583_DLL, CallingConvention = CallingConvention.Cdecl)]
public static extern bool InitializationRq(...)
}
What should I do?
A common issue when deploying .Net applications that have native dependencies, is that the native dlls may be missing dependencies themselves on the target machines e.g. the correct version of the C runtime.
Use a tool such a Dependency Walker to analyze your native dll and determine if it has a missing dependency on the machine you have copied it too.
Try not to hard code any paths in the DllImport attribute parameter that specifies the name of the file. Then you should make usre the file is right besides the executable.
Something like this:
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
Move the DLL to the root. If that works, then look at your attribute to determine why. You haven't posted any code, so I can't give you any specific reason.