How do I export the methods of a native class defined in a C++/CLI project? Here's what I have:
The .h file:
#pragma once
#ifdef COMPILE_PRODUCER_LIB
#define PRODUCER_LIB_EXPORT __declspec(dllexport)
#else
#define PRODUCER_LIB_EXPORT __declspec(dllimport)
#endif
public class PRODUCER_LIB_EXPORT MySecondNativeClass {
public:
MySecondNativeClass(int val);
int getValue() const;
private:
int m_value;
};
The .cpp file:
#include "stdafx.h"
#include "MySecondNativeClass.h"
MySecondNativeClass::MySecondNativeClass(int val) {
this->m_value = val;
}
int MySecondNativeClass::getValue() const {
return this->m_value;
}
Using this class in the same project works fine, but using it in another (C++/CLI) project gives me "unresolved external symbol" linker errors. (COMPILE_PRODUCER_LIB is a preprocessor definition defined only in the project that contains the class.)
I've created a small solution (for Visual Studio 2010) that shows the problem (download at the end of this page). There, the native class MySecondNativeClass is defined in the project "ManagedProviderLib" and is being used in "ExternalTestClass.cpp" (in project "ManagedExternalLib").
Your DLL project creates a .lib file in the build directory, the DLL's import library. You need to specify that .lib file in the other project, Linker + Input, Additional Dependencies setting.
Note that Add Reference cannot work, the assembly metadata only contains definitions for managed classes. Your class is native C++, not managed. Also make sure that your .cpp file is compiled without /clr in effect. The C++/CLI compiler will happily translate native C++ classes to IL but that is not very efficient. You can control this within the source code file with #pragma managed.
Related
The scenario is new and I believe it might be a bug in cpp-winrt module or the vc compiler.
The Problem
1. Create a "windows runtime component" using the cpp-winrt template for universal windows.
2. Note the namespace name defined in the idl file. By default the idl file is named as class.idl.
3. Add a "new standard cpp class" to the project using the class wizard.
4. Put the new class under the same namespace name as defined in the idl file.
5. Build the project.
a. The build should succeed.
6. Use the standard cpp class in the runtime implementation class.
7. Now try to build the project again.
a. The build will fail this time.
The Reason
1. cppwinrt.exe generates source files from the idl file.
2. The runtime implementation class namespace is prefixed by "winrt".
3. The standard cpp class is not prefixed by the namespace "winrt".
4. The vc compiler expects the standard cpp class namespace to start from "winrt"
5. Otherwise the name resolution fails even if you try to use the fully qualified namespace name.
Example runtime idl file
namespace NMLevel1.NMLevel2
{
[default_interface]
runtimeclass Class
{
Class();
void RuntimeMethod1();
Int32 RuntimeMethod2(Int32 arg1);
String RuntimeMethod3(String arg1);
Int32 MyProperty;
}
}
Example standard cpp file
#pragma once
#include <string>
using namespace std;
namespace NMLevel1::NMLevel2
{
class StdCPPClass
{
public:
StdCPPClass();
virtual ~StdCPPClass();
void method1();
int method2(int arg1);
wstring method3(wstring arg1);
};
}
Example runtime class implementation
#include "pch.h"
#include "Class.h"
#include "NMLevel1.NMLevel2.Class.g.cpp"
#include "StdCPPClass.h"
using namespace winrt;
using namespace Windows::Foundation;
namespace winrt::NMLevel1::NMLevel2::implementation
{
void Class::RuntimeMethod1()
{
NMLevel1::NMLevel2::StdCPPClass stdcls;
Uri uri(L"http://aka.ms/cppwinrt");
//printf("Hello, %ls!\n", uri.AbsoluteUri().c_str());
printf("RuntimeMethod1(): Hello, %ls!\n", stdcls.method3(uri.AbsoluteUri().c_str()).c_str());
}
}
NMLevel1::NMLevel2::StdCPPClass stdcls; is not allowed without prefixing the namespace with winrt.
Is this a bug or a design limitation that cannot be overcome?
or How can I use the same namespace 'NMLevel1::NMLevel2' in idl and cpp files?
Name lookup in C++ is fairly involved, especially when namespaces get essentially merged through using declarations. To help the compiler identify the name you want, you'll have to be explicit, and use a fully qualified name (as opposed to a qualified name, as in the sample).
You'll have to change
void Class::RuntimeMethod1()
{
NMLevel1::NMLevel2::StdCPPClass stdcls;
// ...
}
to
void Class::RuntimeMethod1()
{
::NMLevel1::NMLevel2::StdCPPClass stdcls;
// ...
}
Note the leading :: scope resolution, which limits lookup to the global scope (or namespaces introduced into the global namespace through a using declaration). You'll find additional information here: Qualified name lookup.
I have an interface in C++/CLI I need to implement in C#, but I it is not visible. However I have other classes (abstract and concrete that I can inherit from).
My C++/CLI Interface:
namespace MyNamespace { namespace MySubnamespace {
public interface class ITestInterface
{
public:
property bool FirstProperty
{
bool get();
}
property bool SecondProperty
{
bool get();
}
};
}}
I have a Test project where I use all the functionality in my Managed Library, but the Interface never becomes visible.
How I try to use it in my C# Test project: (I tried using it from a Class Library Project also, and it doesn't work either).
public class Test: MyNamespace.MySubnamespace.ITestInterface
{
}
I get "Cannot resolve symbol 'ITestInterface'"
What am I missing?
Update
I kept trying different things following the comments to my question, and I found that if I include my .h file in some other .h file of my C++/CLI project, the class becomes visible.
Basically I just do:
#include "ITestInterface.h"
In one of my other .h files of the C++/CLI project and the Class becomes visible to the c# project.
Is there a way I could avoid doing that?
C++/CLI is similar to C++ in that only .cpp files are compiled directly. Header files are only compiled when included. This is why adding an #include for your interface header works.
There are several ways to make sure your code is included for a C++/CLI class:
Have both a .h and .cpp file (even if the .cpp file only includes the .h file it corresponds to)
Have only include files and then include all of the headers in one .cpp file (which may be empty other than the includes)
Have only .cpp files (which is fine if the other code does not reference this code)
I just bought a device that comes with a dll file. I want to use Visual C++ to program the device. How do I load the .dll file into my project?
A DLL is a library file that contains compiled program logic, just like an EXE. You can't execute it alone, but like an EXE file you can't just 'load' it into your project either.
You will need to use functions like Load Library to load the library, and then GetProcAddress to find a function you want to call.
Edit:
After you clarified your question in the comments you are trying to write a windows program instead of a program you run on your device.
I wrote some sample code to show you how to start:
#include <windows.h> // This is a windows header file. The functions I mentioned above are declared here
#include "mpusbapi.h" // This is the header file supplied. It declares the function prototypes that are defined in the DLL
int main(int argc, char* argv)
{
// Try to load the library
HMODULE mpbusDLL = NULL;
mpbusDLL = LoadLibrary(L"mpusbapi.dll");
if (mpbusDLL != NULL) {
// If the library could be loaded, then load the functions using GetProcAddress()
// Load the function 'MPUSBOpen' from the DLL
MPUSBOpen = (HANDLE(*)(DWORD, PCHAR, PCHAR, DWORD, DWORD)) GetProcAddress(mpbusDLL, "_MPUSBOpen");
...
MPUSBOpen(...);
}
}
This C code will load your libary and then attempt to load the function MPUSBOpen, which is implemented in your DLL.
You will need to load the other functions defined in your header file the same way (at least if you want to use them).
I have a unmanaged C++ dll for which I do not have access to code but have all methods declarations for.
Lets for simplicity say that .h looks like this:
#include <iostream>
#ifndef NUMERIC_LIBRARY
#define NUMERIC_LIBRARY
class Numeric
{
public:
Numeric();
int Add(int a, int b);
~Numeric();
};
#endif
and method implementation in .cpp file
int Numeric::Add(int a, int b)
{
return (a + b);
}
I simply want to call the add function from C++ in my C# code:
namespace UnmanagedTester
{
class Program
{
[DllImport(#"C:\CPP and CSharp Project\UnmanagedNumeric\Debug\numeric.dll", EntryPoint = "Add")]
public static extern int Add(int a, int b);
static void Main(string[] args)
{
int sum = Add(2, 3);
Console.WriteLine(sum);
}
}
}
After trying to execute I have the following error:
Unable to find an entry point named 'Add' in DLL 'C:\CPP and CSharp Project\UnmanagedNumeric\Debug\numeric.dll'.
I CAN NOT change C++ code. Have no idea what is going wrong.
Appreciate your help.
Using PInvoke you can only call global functions exported from Dll. To use exported C++ classes, you need to write C++/CLI wrapper. This is C++/CLI Class Library project, which exposes pure .NET interface, internally it is linked to unmanaged C++ Dll, instantiates a class from this Dll and calls its methods.
Edit: you can start from this: http://www.codeproject.com/KB/mcpp/quickcppcli.aspx#A8
If you need to create a wrapper, take a look at swig.org. It will generate one for most high level language like C#.
I just came across this program a few minutes ago while working the same problem that you are.
To use a class from native C++ from C# you need a C++/CLi wrapper in between, as mentioned by by previous answers. To actually do that, it is not very straight forward. Here is I link that tell you how to do it at a high level: C++/CLI wrapper for native C++ to use as reference in C#.
If you are quite new to this (like me), you might stumble on 1) -- the linking part. To solve that, you can see how I did here (see my question portion): Link error linking from managed to unmanaged C++ despite linking to .lib file with exported symbols
So I just began to try my hand at emulation after years of putting it off and not knowing where to start and I have managed to successfully write my first emulator! Now I am organizing my code in so that I can reuse the code to emulate other systems. I've been toying with the idea of having a shared frontend "platform handler" of sorts that I will compile as my executable whereas I will compile my emulated system code into dlls that the platform handler will use to identify what is available and instantiate from. This would allow me to separate my code into different projects and to leave the option open of using a bulkier front-end with more features or a streamlined "game only" and to share the same dlls between them rather than make two different solutions.
I know how to compile dlls vs executables but I don't know how to link the executable to the custom dll in such a way that I can instantiate a class from it. I'm not even sure what I'm trying to do is technically possible. Do the dll classes need to be static? I've never coded anything like this before or even done much with custom dlls so any help or ideas would be appreciated. I'm using Visual C++ 2010 by the way. Thanks in advance for any advice anyone may have.
You don't really have to do much different. Just export your classes from the dll like you do for functions. In your app, include the header and link to the generated lib like you usually do. See this page: http://msdn.microsoft.com/en-us/library/81h27t8c%28v=vs.80%29.aspx
Example.h
#ifdef DLL_EXPORT
#define EXPORT_API __declspec(dllexport)
#else
#define EXPORT_API __declspec(dllimport)
#endif
class EXPORT_API Example
{
public:
Example();
~Example();
int SomeMethod();
};
int EXPORT_API ExampleFuncion();
Example.cpp
#include "Example.h"
Example::Example()
{
// construct stuff
}
Example::~Example()
{
// destruct stuff
}
int Example::SomeMethod()
{
// do stuff
return 0;
}
int EXPORT_API ExampleFunction()
{
return 0;
}
In your dll project, define DLL_EXPORT and build. You will get a .lib and .dll output. In your main project where you will be using the dll you do not have to do anything except include the header and link against the .lib. Do not define the DLL_EXPORT symbol in your main project and be sure the .dll is somewhere your application can find it.
If you really want to get clever, this problem is screaming for the factory design pattern. If you design your interface well enough, you can have your dlls register their implementation with your application when they are loaded. You can extend forever without even rebuilding your main executable.