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.
Related
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 have one project which capture images from multiple cameras which is in C++ .I want to use that project in my new project which is in C#.I had made dll of that project.My question is ,how can i use that dll in my project.I know by passing window handle to C++ dll we can use it but i dont know how to do it and what changes should i make in dll.
Please forgive ,if it is foolish question.
I had the exact problem as you and this article helped me.
http://blogs.msdn.com/b/jonathanswift/archive/2006/10/03/dynamically-calling-an-unmanaged-dll-from-.net-_2800_c_23002900_.aspx
To pass the handle, you can add another function in C++ end. Something like,
(in the header)
extern "C" __declspec(dllexport) void SetParent(HWND hWnd);
To use the SetParent in C#
class Program
{
...
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
private delegate void SetParent(IntPtr hWnd);
public void testMethod()
{
...
IntPtr getAddress = NativeMethods.GetProcAddress(pDll, "SetParent");
...
SetParent setParent = (SetParent)Marshal.GetDelegateForFunctionPointer(getAddress, typeof(SetParent));
setParent(this.Handle);
...
}
}
If your C++ project is already in a DLL you can call any functions that it exports using P/Invoke. You will have to declare the method in your C# assembly as shown below, but then you can call it like a standard static method.
[DllImport("YourDllsName.dll")]
public static extern bool FunctionThatAWindowHandleAndReturnsBool(IntPtr hWnd);
Depending on the types of parameters that your C++ DLL's functions take the marshaling of the .Net datatypes to C data types can get complicated.
I am trying to call a function from a DLL generated in LabVIEW. I thought this was going to be far more straightforward than it is turning out to be. The function is described below:
void __cdecl Device_Init(char DevName[]);
So in my C# code I am trying the following:
[DllImport(#"Device.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern void Device_Init(StringBuilder name);
I call this in my application by simply using the following:
StringBuilder devName = new StringBuilder(DeviceName);
Device_Init(devName);
Rather than getting any initialization on my device, I see a LabVIEW vi window pop up that has a title akin to a different method within the dll (i.e. AF1_GetPressure.vi). The application then hangs with this LabVIEW window popped up and I have to exit the debugging session.
I guess my question is how my function signature might be erroneous... I used StringBuilder as I found an example on the NI website that seemed to indicate that LabVIEW requires this variable type to better ascertain the number of characters in the array. http://www.ni.com/example/31050/en/
I have tried all kinds of different combinations of parameter types but I simply can't seem to get this to work. If I try calling the dll from C++ then I can get things to work. Although, oddly, I had to dynamically load the dll in C++ because I was getting a dll initialization failure when I tried to load it with the application.
Any help would be greatly appreciated!
I was able to build a DLL with LabView 2012, and import it into a .NET 4.0 console application, call the function, and receive a result. Here is a screenshot of the VI:
And here is the import statement in C#:
[DllImport(#"SharedLib.dll", CallingConvention = CallingConvention.Cdecl)]
private static extern int StringLength(string str);
I would recommend trying something very simple like this and see if you can get it working.
I should note that I tried passing my parameter as a StringBuilder object and that worked as well - and I didn't expect it to!
Also, I recommend posting this question on the LabView forums. I was always able to get a very quick response there, and I think with LabView, you're likely to get a better response there than StackOverflow.
As requested, here are the contents of the .h file generated by LabView:
#include "extcode.h"
#pragma pack(push)
#pragma pack(1)
#ifdef __cplusplus
extern "C" {
#endif
/*!
* StringLength
*/
int32_t __cdecl StringLength(char String[]);
long __cdecl LVDLLStatus(char *errStr, int errStrLen, void *module);
#ifdef __cplusplus
} // extern "C"
#endif
#pragma pack(pop)
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();
I have an ActiveX control written in C# and working when run in an ActiveX compatible program (CoDeSys). The problem I've come across is that in order to allow CoDeSys to interact with the ActiveX control, CoDeSys requires the dll to export the function prototype:
void ExecuteActiveXCall(IUnknown* pUnk, char* pszId, char* pszParam, char* pszReturnBuffer, int nReturnBufferSize, DWORD* pdwReturnFlag);
I've looked without success on how to export this like you can in C++, as shown in this example:
extern "C" __declspec (dllexport) void ExecuteActiveXCall(IUnknown* pUnk, char* pszId, char* pszParam, char* pszReturnBuffer, int nReturnBufferSize, DWORD* pdwReturnFlag)
{
if (strcmp(pszId, "IWebBrowser|GoBack") == 0)
{
IUnknown* pNewUnk;
IWebBrowser* pwb;
pUnk->QueryInterface(IID_IWebBrowser, (void**) &pNewUnk);
pwb = (IWebBrowser*) pNewUnk;
if (pwb)
{
pwb->GoBack();
pwb->Release();
}
}
else if (strcmp(pszId, "IWebBrowser|GoForward") == 0)
{
IUnknown* pNewUnk;
IWebBrowser* pwb;
pUnk->QueryInterface(IID_IWebBrowser, (void**) &pNewUnk);
pwb = (IWebBrowser*) pNewUnk;
if (pwb)
{
pwb->GoForward();
pwb->Release();
}
}
}
C# does have an extern keyword, but it doesn't allow you to provide the function definition (at least I haven't found a way). After attempting this:
extern unsafe void ExecuteActiveXCall(
[MarshalAs(UnmanagedType.IUnknown)] object pUnk,
char* pszId,
char* pszParam,
char* pszReturnBuffer,
int nReturnBufferSize,
UInt32* pdwReturnFlag)
{
}
The following error occurs:
'AlarmsCSharp.AlarmsControl.ExecuteActiveXCall(object, char*, char*, char*, int, uint*)' cannot be extern and declare a body
Has anyone attempted exporting a function in a C# dll?
Are there any workarounds? (I had the thought of [DllImport("AlarmsCSharp.dll")] and calling C# in the C++ dll, but figured I'd see if anyone had a solution before)
Perhaps I'm over thinking this and don't need to export this function since the ActiveX control is able to interact already with the C# code.
EDIT: I have a feeling my translation from the C++ function prototype to the C# interface declaration. If someone with more experience with C++/C# programming could verify that I did that translation correct or incorrect, it may be of some help.
You say that CoDeSys is ActiveX-compatible; have you tried using COM interop?
There seems to be 3 main options; the first is to set up COM interop where you can instantiate your C# control / class using COM. I'm sure if you do some searching you can find some more info on that.
The second option is to make your c++ module mixed managed/unmanaged, as described here:
http://social.msdn.microsoft.com/Forums/en-US/vclanguage/thread/5345a27a-a614-4a74-9f6d-ea7a999ddf83/
The third option is to use "reverse PInvoke" as described here: http://tigerang.blogspot.com/2008/09/reverse-pinvoke.html
There may be other options; those are the ones I know of.