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Importing C++ custom library functions into C#

I currently have a large C++ library that I need to incorporate into a C# project. I was successful in using DllImport to get access to some functions from my library, like this:
[DllImport("MyLib.dll")]
public static extern int SampleFunction(string param);
However, I can't seem to figure out how to make it work for functions that either have a parameter or return type that is not defined within the dll itself (i.e., the code in the dll imports it from another file), such as this example function that takes in a list:
[DllImport("MyLib.dll")]
public static extern std::vector<MyClass> MyFunction(string param);
For std library functions, I know I can get the dll and import that in, but what about other classes like MyClass in the above example? Do I need to create a managed wrapper class in C++ for each of these classes, or is there another way to do this?

std::vector<MyClass>, or indeed any unmanaged C++ class, cannot be used for interop to C#. Indeed, even if you wished to consume this function from another unmanaged C++ module you'd have to make sure that you were using the same compiler and dynamic runtime as the DLL which exported the function.
You'll need to find some other way to implement this functionality. There are lots of different ways to do that.
You could expose a p/invoke interface to the functionality. That would likely involve declaring a struct to represent the data of your class, and serializing to and from that struct.
You might consider a COM interface but it won't offer great advantages over p/invoke. You'd still need to serialize your class.
A C++/CLI wrapper would be yet another option. You'd wrap the unmanaged class with a managed C++/CLI class, and then consume that from the C#.

If you need a custom class from a native lib, you'll probably need to export a type library or use managed C++ to write a wrapper. What you're effectively trying to do is marshal a piece of memory from native to managed and now have to deal with how the data type is marshaled.
If at all possible, I would actually recommend trying to do away with the marshaling as when it works it's fine, but when it breaks, it can be rage inducing to debug.
Regardless, I'm actually not sure if anything in the STL can be marshaled. At the very least, I have never seen it done. More times, I've had to do a conversion like so: How can I marshall a vector<int> from a C++ dll to a C# application?
If you want to marshal an actual class, the standard way I've done it up until now is through a type library: Import TLB into C#
Or by linking a native lib into a managed C++ class and then referencing the managed C++ dll into the C# project as a shim.
Beyond that, if you can convert the class to strict C-style functions and pass a struct around, that could allow you to just use pinvoke, this is no different from simply exporting a bunch of helper functions except you can marshal a struct representation back and forth: Marshal C++ struct array into C#

Declaring a struct, usable from C#, in managed C++

I have a scenario where a C# library is consuming a mixed mode C++ library. The use case is as follows:
1) The C# code initializes a listener from the library (managed c++), which initializes a listener from native C++.
2) The native code receives a message and parses it, then passes it to the managed c++ via IJW code
3) The managed c++ calls a delegate from the C# code with the message
This all works fine, except for the very last part - actually including the message. The C# code can't access the data type defined in the managed C++. When you navigate to the struct's definition, it looks like this:
namespace NativeWrapper
{
[CLSCompliant(false)]
[NativeCppClass]
[UnsafeValueType]
public struct MyDataType
{
}
}
As you can see - it decries it as unsafe and wipes out the fields. I've seen solutions to this problem where a third library, in C#, declares a struct, and both the C# and the managed C++ use it. I imagine that would work, but I'm trying to avoid creating a third library for one small file...this component is part of a large system, I'd like to keep the number of DLLs I'm adding to it as small as possible.
So, the question is, is there a way I can define a struct in managed C++ that the C# code can references? I know how to define a ref class, that's how my listener is set up, but I'd like this to be a struct.

C# classes exposed from javascript through Firebreath Framework

I need to create the classes in C# and call that classes from javascript through C++CLI and Firebreath Framework .. create the complex hierarchy class structure and expose it from javacsript
The flow should be :
Javascript <-- C++(FireBreath)<-- C#
C#-->C++(Firebreath)-->Javascript
I have to create the generalized solution for this problem.
Then how should i implement this? If you have any solution,sort of information ,ways to solve this problem then please let me know..
Suppose my Class Library in C# which includes the classes like :
public class TestImage
{
}
public class DrawImage
{
public void ShowImage(TestImage testImage)
{
}
}
Here I need to call ShowImage(TestImage testImage) method from JavaScript page of Firebreath Framewaork.
I already created the wrapper but I dont have an idea to expose the class object as argument to the method like the above ShowImage () in tjhe JavaScript page of the Fireabreath Framework.
If you have any idea related to this please let me know.

When you say "generalized solution"... do you mean a tool or process that automates this?
I believe this is possible. Here's how I would do it:
I'm assuming you have gotten started with FireBreath and have some understanding of it. I'm glossing over countless problems you'll run into integrating all this within a FireBreath solution; that would take days! So this is just architectural advice. I'm sorry to omit so many details.
I would write a tool that dynamically loads your .NET assembly or assemblies, and uses reflection to traverse the 'complex hierarchy class structure'. This tool would generate two things: A C++/CLI wrapper for your .NET library, and a set of native C++ FireBreath classes that bind from Javascript to that C++/CLI wrapper.
The C++/CLI wrapper (see enter link description here) makes your .NET library callable from the native C++ of FireBreath.
Actually, here is a tool on CodePlex that claims to generate such a wrapper.
The Javascript adapter is a set of .cpp modules (probably one for each of your library/C++/CLI classes). Each of these is a C++ class derived from FB::JSAPIAuto, which allows these classes to be instantiated as Javascript objects. Within the constructor for each of these classes, the automated tool inserts code to create the object's Javascript API. Code that looks like this:
registerMethod("Start", make_method(this, &thisClass::Start));
registerMethod("Abort", make_method(this, &thisClass::Abort));
registerProperty("Size", make_property(this, &thisClass::get_Size,&thisClass::set_Size));
The automated tool must synthesize these methods of the class, like thisClass::Start and thisClass::set_Size. Their parameters and return types are the Javascript-compatible types supported by FireBreath - like int and double and bool, but also std::string, FB::VariantMap and FB::VariantList. In the body of each such method, the tool generates code to call the corresponding C++/CLI wrapper API, doing any necessary conversion between parameters and returns.
I suppose that each FB::JSAPIAuto-derived class inherits from, has as a member, or holds a pointer to, the C++/CLI class/object it represents.
As a FireBreath project, your .NET library is ultimately represented by a GUID - this is how Javascript finds its way into your library, by creating a root object from that GUID. It then calls methods or reads properties of that object to get other objects, and so on to access your entire library API.
I suppose there will be some issues mapping between Javascript and C#. You will have to study the Javascript parameter and return types supported by FireBreath, and limit your C# API accordingly. Probably key is figuring out how Javascript objects and arrays are represented as they cross the C++/CLI layer.

I've just achieved something like this using COM. I exposed the C# library as a COM object, then wrote a couple of wrapper functions which called this library in FireBreath. (I was lucky thought I had a very simple API).

Object sent from C++/CLI to C#?

My friend build an application ( console app) in C++/CLI.
I'm programming in C#.
Ive build for him some DLL in C# which does some calculations based on params that he send.
My function (inside my C# dll) looks like this :
bool LongCalc(dynamic obj)
{
...
}
(again , the obj needs to be sent from his c++/cli to my c# dll).
my question :
If he creates an object in his cpp like :
cppObj
{
prop1 , prop2 , prop...n
}
would I be able to read his obj in my c# as :
obj.prop1
obj.prop2 .... ?
what should he or me need to do in order for me to work with his obj ?

If he's using your C# DLL from his C++ application then I'm guessing he's using managed C++. If that's the case then it'd make sense for him to define his C++ class as a managed C++ class so that you'll be able to invoke methods against it.

The answer highly depends on how your friend is consuming your C# dll.
If he's using plain C++ and consuming your .NET assembly through .NET COM Interop, then I don't think a dynamic parameter will be supported for a plain C++ class like CppObj from your example, becuase there is no way to know how to invoke the object's methods during run time.
In order for this to work with a dynamic parameter in the C# side, the C++ class will probably have to be a COM object and implement IDispatch, so that the CLR will have the ability to dynamically invoke methods on the C++ object.
I'm not 100% sure that dynamic actually supports IDispatch in COM Interop, but I see no theoretical reason why it shouldn't.

How to create a .dll in Visual Studio 2008 for use in a C# App?

I have a C++ class I'd like to access from a C# application. I'll need to access the constructor and a single member function. Currently the app accepts data in the form of stl::vectors but I can do some conversion if that's not likely to work?
I've found a few articles online which describe how to call C++ DLLs and some others which describe how to make .dll projects for other purposes. I'm struggling to find a guide to creating them in Visual Studio 2008 for use in a C# app though (there seem to be a few for VS 6.0 but the majority of the options they specify don't seem to appear in the 2008 version).
If anyone has a step-by-step guide or a fairly basic example to get going from, I'd be very grateful.

The easiest way to interoperate between C++ and C# is by using managed C++, or C++/CLI as it is called. In VisualStudio, create a new C++ project of type "CLR Class Library". There is some new syntax for the parts that you want to make available to C#, but you can use regular C++ as usual.
In this example, I'm using std::vector<int> just to show that you can use standard types - however, in an actual application, I'd prefer to use the .NET types where possible (in this case a System::Collections::Generic::List<int>).
#pragma unmanaged
#include <vector>
#pragma managed
public ref class CppClass
{
public:
CppClass() : vectorOfInts_(new std::vector<int>)
{}
// This is a finalizer, run when GC collects the managed object
!CppClass()
{ delete vectorOfInts_; }
void Add(int n)
{ vectorOfInts_->push_back(n); }
private:
std::vector<int>* vectorOfInts_;
};
EDIT: Changed the class to hold the vector by pointer instead of by value.

If such DLL is unmanaged. You will have to use P/invoke. A p/invoke function definition looks like this:
[DllImport("Library_Name.dll", EntryPoint = "function")]
public static extern void function();
If, on the other hand, is a managed (C++/CLI) DLL (or assembly). You can access it by adding a reference to it on your .NET project.
EDIT:
I think I didn't answer your question at all. But to create a managed C++ DLL to be accessed from .NET, create a new project an choose:
Visual C++/CLR/Class Library. And then, just add its output DLL to your C# project.
That'd do it. :)

Do you have an existing C++ exe that you want to re-build as a dll? Or is all you have the C++ class?
If all you have is the C++ class, you might think about building a .Net dll. While you couldn't pass stl types from C# to C++, I am pretty sure you can pass managed .Net types.
If you must use the stl types in the class, you could convert the data in the C++ class, or the calling app.

I've found a tutorial which works. A quick note though, you have to be careful to copy the .dll into the same directory as the executable. I messed around with trying to tell the executable where the DLL was but gave up in the end.

Use of unmanaged C++ Dlls can be very tedious in C#.
An "easier" route is to place it in a COM wrapper.