I'm trying to call from C# a function in a custom DLL written in C++. However I'm getting the warning during code analysis and the error at runtime:
Warning: CA1400 :
Microsoft.Interoperability : Correct
the declaration of
'SafeNativeMethods.SetHook()' so that
it correctly points to an existing
entry point in 'wi.dll'. The unmanaged
entry point name currently linked to
is SetHook.
Error:
System.EntryPointNotFoundException was
unhandled. Unable to find an entry
point named 'SetHook' in DLL 'wi.dll'.
Both projects wi.dll and C# exe has been compiled in to the same DEBUG folder, both files reside here. There is only one file with the name wi.dll in the whole file system.
C++ function definition looks like:
#define WI_API __declspec(dllexport)
bool WI_API SetHook();
I can see exported function using Dependency Walker:
as decorated: bool SetHook(void)
as undecorated: ?SetHook##YA_NXZ
C# DLL import looks like (I've defined these lines using CLRInsideOut from MSDN magazine):
[DllImport("wi.dll", EntryPoint = "SetHook", CallingConvention = CallingConvention.Cdecl)]
[return: MarshalAsAttribute(UnmanagedType.I1)]
internal static extern bool SetHook();
I've tried without EntryPoint and CallingConvention definitions as well.
Both projects are 32-bits, I'm using W7 64 bits, VS 2010 RC.
I believe that I simply have overlooked something....
Thanks in advance.
Well, you know the entry point name, use the EntryPoint = "?SetHook##YA_NXZ" property in the [DllImport] attribute. Or put extern "C" before the declaration in your C++ code so the name doesn't get mangled.
[DllImport("wi.dll", EntryPoint = "?SetHook##YA_NXZ", CallingConvention = CallingConvention.Cdecl)]
[return: MarshalAsAttribute(UnmanagedType.I1)]
internal static extern bool SetHook();
CallingConvention.Cdecl means C not C++, so when you have a function with a C++ decorated name, you need to use the decorated name as your EntryPoint or use Extern "C" in The C++ code declaration to turn off C++ name decoration.
Related
I read all the questions and answers related to passing unique_ptr as argument to a class constructor and those answers worked for classes within the exe. But here im trying to pass an unique_ptr object to a class constructor that is pre-compiled as static library.
This class in the library looks something like this,
// Class declaration (in a header file)
class TScreen
{
private:
std::unique_ptr<TProcess> m_process;
public:
__fastcall TScreen(int a, std::unique_ptr<TProcess> i_process);
};
// The constructor definition (in a separate .cpp file)
__fastcall TScreen::TScreen(int a, std::unique_ptr<TProcess> i_process):
m_process(std::move(i_process))
{
}
I will be trying to instantiate the class TScreen in the exe like this,
void TScreen_Main::CallScreen()
{
std::unique_ptr<TProcess> objprocess (new TProcess());
std::unique_ptr<TScreen> objscreen (new TScreen(0, std::move(objprocess)));
}
I compiled the library and imported it to the exe. When i compile the exe, it gives me a link error like this,
[ilink32 Error] Error: Unresolved external '__fastcall TScreen::TScreen(int, std::unique_ptr<TProcess, std::default_delete<TProcess> >)' referenced from TSCREEN_MAIN.OBJ
[ilink32 Error] Error: Unable to perform link
I tried the same with boost::shared_ptr as well and it gives me the same error. But it works fine with raw pointers, but not with smart pointers and i cannot figure out why?
Thanks in advance.
Your problem here is a linking issue. Now, exactly what's going on is difficult for me to say because I never work in a Windows environment, and linking is something that (while very similar) has some distinct differences between a Unix/Linux and a Windows environment.
My guess is that if you explicitly declare your constructor to be inline, and declare that the definition is inline, it will work correctly.
This presumes that the fact that you put the declaration of the class and definition together indicates that the definition is in the header file with the class.
When the compiler sees that it's declared inline it will emit a definition into every compilation unit where it's needed. The linker should then eliminate all the duplicate definitions.
If you really are defining the constructor in some .cpp file separate from the .hpp file that the class is in, and you compiler that .cpp file into .obj file that eventually makes it into a .lib or .dll that you link against when creating the executable, then I don't know what the problem is. If this is the case, you should use the tools that should come with your development environment to see what symbols are actually in the library or the dll because somehow the symbol for the constructor definition isn't there.
I'm currently remodelling a dynamic library project and removed a lot of STL and other dependencies from its header resulting in conflicting implementations between different toolchains.
The DLL Interface now only contains plain C-types and custom types whom implementation depends solely on the DLL code. But now I'm stuck with two remaining points.
The DLL should return some sort of reference counting smart pointer (with a weak pointer option)
Managing construction and destruction between the DLL boundaries. This more or less looks like this.
.
#include <memory>
class Config;
typedef std::shared_ptr<Config> ConfigPtr;
class CONFIGAPI_DLL Config
{
public:
///...
ConfigPtr getNewNode( char const* query = "." )
{
// construct obj in dll, but construct shared_ptr in header
return ConfigPtr( _constructgetNewNode(query) );
}
ConfigPtr getNewNodeFromHeader( char const* query = "." )
{
// construct obj and shared_ptr in header
auto obj = new Config;
obj->_init(query);
return ConfigPtr( obj );
}
private:
Config* _constructNewNode( char const* query = "." );
void _init( char const* query = "." );
};
I was thinking by creating the share_ptr at the dll headers (getNewNode) it would prevent mixed implementations of std::shared_ptr ...but I don't know if that is a good idea?
But I also construct the new object inside the DLL (_constructNewNode) and this means it should also be destructed there?
I tried to construct it in the headers and so in the user code scope (getNewNodeFromHeader)... this shouldn't cause problems?
The downside is I still export the C++11 header and rule out all older compilers. Is it possible to export the shared_ptr type from the dll as unconflicting code but still be compatible with std::shared_ptr?
thanks!
I suppose you want to mix creation and destruction of the objects (Config and the shared_ptr). If the DLL client is not compiled with the same version and configuration of the compiler you would be in troubles (for example, mixing debug and release modules). The main problem I see here: there is not any type of standard ABI for C++.
I was thinking by creating the share_ptr at the dll headers
(getNewNode) it would prevent mixed implementations of std::shared_ptr
...but I don't know if that is a good idea?
If you define your header file to create the shared_ptr, that would be OK if only a module use that header file. I mean, if the shared_ptr is not to be used for the content of the DLL, for example. BUT if other client module (a binary module, like other DLL) use also that header, you must be sure they are compiled with the same compiler and compiling configuration. If you have not that guarantee, then is not good idea.
But I also construct the new object inside the DLL (_constructNewNode)
and this means it should also be destructed there?
If you construct the object inside the DLL, you'll be better destroying inside the DLL. How to do that? specifying a deleter at shared_ptr construction. Something like
struct ConfigDeleter {
void operator()(Config* c) {
c->destroy(); // or as you want to implement it.
};
typedef std::shared_ptr<Config, ConfigDeleter> ConfigPtr;
I tried to construct it in the headers and so in the user code scope
(getNewNodeFromHeader)... this shouldn't cause problems?
As before, it depends if you can guarantee all modules are homogeneous (same compiler version and configuration, library, etc.). But of you want to implement as that, do it well:
// construct obj and shared_ptr in header
auto obj_ = make_shared<Config>();
obj_->init(query);
It is exception-safe and more efficient: just one allocation to store the object and the reference, instead two allocations in your sample.
If you want your code be safe for mixing modules, implement all allocations (shared_ptr included) into the DLL, if they are shared. Exports a "C" interface, and create header file to wrap that interface in classes. Something like:
class WConfig {
public:
WConfig(): m(IDll->create()) {
}
// other member functions as interface stub
~WConfig() {
IDll->release(m);
}
private:
Config* m;
};
To share this object, you can use copy constructor (that copy the pointer and call to IDll->reference(m), for example) or any other approach.
I'm using C++/CLI only to unit test unmanaged C++ code in VS2010. I switched the compiler to /clr and using the unmanaged code from a static library.
I have a simple int property in my test class.
I would like to pass that as a const int & to a function in native C++. But it can't compile and I've found out that, it's because you can't mix references like that.
What is the way to do it, I tried to following and it's working, but is there a nicer way?
[TestClass]
public ref class MyTestClass
{
private:
int _my_property;
public:
[TestMethod]
void MyTestMethod()
{
MyNativeClass c;
// c.SomeMethod(_my_property) this doesn't work
int i = _my__property;
c.SomeMethod(i) // this works
}
}
C++ references are really just syntactic sugare for pointers. A C++ pointer points to a specific point in memory, while CLI references can be freely moved around by the garbage collector. To pass a reference to an object in managed memory to unmanged code, you need to pin the pointer.
More info and sample in another SO question: Convert from C++/CLI pointer to native C++ pointer
Edit 2
I'm removing the additional information, since it is obviously wrong (thanks #Tergiver and #DeadMG for your comments). I'm also making the post community wiki, so feel free to add any additional correct information.
I have a header file in a managed DLL project like so:
Enums.h:
#pragma once
...
public ref struct ManagedStruct {
Bitmap^ image;
}
...
This header is referenced both from another class in the DLL and from a separate executable. The managed struct alone is generating:
error C2011: 'ManagedStruct' : 'class' type redefinition.
If I move the struct to the main header file in the DLL it works fine, and is publicly accessible, so that's what I'm doing, but I would very much like to learn why this is happening when I just move it to another file.
I have checked all necessary includes and namespaces AND tried the obvious header guards, to no avail; I still get the error.
Thanks very much for any insight!
You have to de-tune the traditional C/C++ header file think a bit when you work with managed code. The principal source of type declarations is the assembly metadata. This is very different from the native C/C++ compilation model where you have to have a header file for types that you make visible to other modules.
I'm going to guess that you get this C2011 error in the EXE project. Where you both added a reference to the DLL project assembly (like you should) and used #include on the header file. Like you should not. That's a guaranteed duplicate definition, #pragma once doesn't fix that.
Don't use header files for exported type definitions. Always use assembly references.
I Know this question is a bit old, but I'm writing this for future usage:
I had the following problem, which was similar:
managed DLL had a managed class.
managed.h:
namespace Managed {
ref class CManagedClass {...}
}
in an unamanged class I wanted to use this above class and so in unmanaged.h
#include "managed.h"
in another DLL I also did:
#include "unmanged.h"
which resolved in the type redefinition error.
I have found a solution to this issue using the following method:
forward declaration in the unmanaged.h
namespace Managed {
ref class CManagedClass;
}
and include the managed.h in the unmanaged.cpp file as usual.
Is it possible to pass a pointer to an object into a DLL, initialize it, and then use the initialized pointer in the main application? If so how? Are there any good articles on the subject, perhaps a tutorial?
I have read this article http://msdn.microsoft.com/en-us/library/ms235460.aspx But that did not seem to get me any where. Maybe I am misinterpreting it...
Yes, this is fine, but assuming your DLL has dynamically allocated the data being pointed to by the buffer, you must be careful about how you free it. There are a few ways to deal with this:
The DLL documents a method by which one should free the data (i.e., CoTaskFree)
The DLL exposes a function that should be called to later free the data
The DLL and the caller are using a common DLL-based runtime; this allows the caller to use the C++ delete operator
Yes.
Assuming you are using Microsoft Visual Studio as your development environment you can export a class rather directly from a dll. Add a define to your dll project something like BUILDING_THE_DLL and the following code snippit will export a c++ class wholesale from the dll.
#ifdef BUILDING_THE_DLL
#define DLLEXPORT __declspec(dllexport)
#else
#define DLLEXPORT __declspec(dllimport)
#endif
class EXPORT DllClass
{
....
};
This is a highly coupled solution and only works if you build the application and its dll using the same development environment, and rebuild both whenever the class definition changes in any way. this method is heavilly used by the MFC library.
To achieve a greater independence between the dll and app, one typically defines a relatively immutable interface and uses that to make builds more independent, and possibly use different build environments.
An implementation in your dll would look something like this:
struct IMyInterface {
virtual void Destroy() =0;
virtual void Method() = 0;
};
class MoDllObject : public IMyInterface
{
// implementation
};
bool EXPORT DllGetInterface(IMyInterface** ppOut)
{
*ppOut = new MyDllObject();
return true;
}