I have a C function, which is part of a VS 2010 project and has this signature:
real_T wrapper(void)
where
typedef double real_T;
In my C# code I attempt this:
[DllImport(#"C:\Users\bla\Documents\Visual Studio 2010\Projects\bla\bla\Debug\bladibla.dll")]
public static extern double wrapper();
static void Main(string[] args)
{
wrapper();
}
but get:
Unable to find an entry point named 'wrapper' in DLL 'C:\Users\bla\Documents\Visual Studio 2010\Projects\bla\bla\Debug\bladibla.dll'.
The dll is definitely there. What else could be wrong?
Possibly the function is being exported with a mangled name. You can suppress the mangling like this:
extern "C" {
real_T wrapper(void);
}
You aren't obviously exporting the function either. The simple way to do that is like this:
extern "C" {
__declspec(dllexport) real_T wrapper(void);
}
If that still doesn't resolve the missing export, use a tool like Dependency Walker to check whether the function is in fact being exported, and if so under what name.
Finally, you should declare the calling convention on the C# side to be cdecl to match the calling convention of your native function.
[DllImport(#"...", CallingConvention=CallingConvention.Cdecl)]
public static extern double wrapper();
Related
I was going to call an unmanaged function in a c++ library from c#, but it crashed. While troubleshooting I narrowed it down to std::wstring. A minimal example looks like this:
C++
#include <iostream>
extern "C" __declspec(dllexport) int __cdecl Start()
{
std::wstring test = std::wstring(L"Hello World");
return 2;
}
C#
using System.Runtime.InteropServices;
internal class Program
{
[DllImport("test.exe", CallingConvention=CallingConvention.Cdecl)]
public static extern int Start();
static void Main(string[] args)
{
var result = Start();
Console.WriteLine($"Result: {result}");
}
}
This gives me a Stack overflow. If I remove the line with std::wstring or I change it to std::string, there is no problem and I get back 2.
Can anyone explain to me what is going on here?
This is something I noticed:
[DllImport("test.exe", CallingConvention=CallingConvention.Cdecl)]
Exporting functions from an EXE instead of a DLL isn't standard. (I think it can be done, but I wouldn't recommend it.)
Build your C++ code as a DLL instead of an EXE. Statically link the DLL with the C++ runtime libraries to avoid missing dependency issues that could arise from not having the right DLLs in the loader search path.
Im trying to call a C function from C# but im getting a BadImageFormatException.
Here is by C function header:
extern "C"
{
__declspec(dllexport) bool validate(char key[]);
}
Here is how im calling it from C#
[DllImport("MyDll.dll")]
static extern bool validate(char[] key);
Whats wrong here.
When calling native methods, you should compile your c# code to 64 or 32 bit explicitely.
project/properties/build/Platform target
Use Dependency Walker to check if 'validate' function is correctly exported from DLL.
You might have not updated the .def file of the DLL project.
I am trying a simple program to access a C function through a dll into a C# program,
class DllImportTest
{
[DllImport("TestApp.dll", EntryPoint = "main1")]
public static extern void main1();
}
class Program
{
static void Main(string[] args)
{
DllImportTest.main1() ;
}
I have seen through the code and the name of the function is the exactly right. I have also tried using Extern "C" but, it throws me an error as its .C file.
I have placed the .Dll in the C# executable folder.
Is there something that I am doing wrong here?
Found it!
I had to use Extern "C" coupled with __declspec(dllexport) . I had never used both together, Thanks guys
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
A call to PInvoke function '[…]' has unbalanced the stack
I'm trying to wrap a few functions written in c++, in order to use them in a c# program (WPF, or as an example a console app), but get run-time exceptions.
I guess this is a compilation issue (of either the c++ project of the C# one). When I change the platform target for the C# projects, I get different exceptions. when the platform target is x64 I get
An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B)
When I try to compile it as x86, I get:
A call to PInvoke function 'Wrapper!Wrapper.IWrapper::create' has unbalanced the stack. This is likely because the managed PInvoke signature does not match the unmanaged target signature. Check that the calling convention and parameters of the PInvoke signature match the target unmanaged signature.
I'm running VS2010 on windows 7 64.
Would be happy for any ideas on how to solve this.
This is what I do:
c++ code. cpp:
int create(int Handle)
{
return 1;
}
and h:
#define EXPORT_DLL __declspec(dllexport)
extern "C"
{
EXPORT_DLL int create(int Handle);
}
Then in a second C# project, I call this dll, where the c++ project's name is wrapAttemptC
namespace Wrapper
{
internal class IWrapper
{
const string SHADOW_DLL_NAME = "wrapAttemptC.dll";
[DllImport(SHADOW_DLL_NAME)]
public static extern int create(int Handle);
}
public class CWW
{
public CWW(){}
public int Connect(int cam)
{
return IWrapper.create(cam);
}
}
}
Then, I put the DLL file created in the c++ project in the bin/Debug of this c# project and of the app c# project (WPF), and try to call
CWW cww = new CWW();
cww.Connect(5);
The default calling convention for C++ exported functions is cdecl, but the default calling convention for the DllImport attribute is WinApi (which defaults to stdcall). So you have a mismatch there that could indeed mess up your stack. Try stating the calling convention explicitly in the DllImport Attribute, your C++ function declaration, or better, both (so that they match). Like this:
EXPORT_DLL __stdcall int create(int Handle);
And in your C# project:
[DllImport(SHADOW_DLL_NAME, CallingConvention = CallingConvention.StdCall)]
I can access a method from a C++ Dll using C# using this method in the C++:
extern "C"
{
__declspec(dllexport) void DisplayHelloFromDLL()
{
printf ("Hello from DLL !\n");
}
}
this works great...but the solution I am working with uses this as the entry point:
extern "C" int WINAPI _tWinMain(HINSTANCE hInstance,
HINSTANCE /*hPrevInstance*/,
LPTSTR lpCmdLine,
int /*nShowCmd*/)
Is there a way I can access this like I have done with the __declspec method?
Cheers
That is not a DLL entry point, that is a primary application entry point. You will need to create it as a new process via CreateProcess.
_tWinMain is actually a #define to either WinMain or wWinMain. You also need to make sure it's actually exported.
That being said, why would a DLL have a WinMain function at all? You should just export a normal function like DisplayHelloFromDLL.
[edit]
The project you are trying to reference -- the one with _tWinMain -- is an EXE (as #DeadMG says). You should not try to import its functions from C# like you do with DLLs; instead you should launch it with Process.Start.
The answer was to call a function created in the C++ using:
extern "C"
{
__declspec(dllexport) void StartAgent()
{
printf ("Starting Agent... \n");
StartServer(true);
RunMainLoop();
}
}
This is then called in the C# using:
[DllImport("myDll.dll")]
public static extern string StartAgent();
StartAgent();
Calling this from the C# and into the C++ gets the application running.