How can I create a struct in C++ put it in a dll and use from C# code? I'm developing an application using C# and C++ where each process talk to each one other using named-pipes and I'd like to share data between via structs (pass raw bytes to process and then cast it to struct type) but rather than define two structs one in C++ and another in C# with same memory alignment, members names and such (which is very error prone, if I update the C++ one and forget the C#'s one) I'd like to creare only one so that there's only one place to change. My idea is (if even possible, I think it isn't not possible due P/invoke limitations) define this struct in a dll written in C++ and just use it from my C# application. This is just my idea; any different approach to solve this is very welcome too.
You can't. Structs and classes are not part of the exposed ABI, the DLL doesn't define them in any way. That's part of the reason for DLL hell in the C/C++ world, your function definitions state the name of the struct they take, but the details of the implementation of that struct aren't actually exposed or defined anywhere in the DLL itself.
C and C++ rely on the use of header files to inform dependent projects of the layout of structs and classes, as that information isn't exposed via the DLL or lib file. Since it's not possible in native code, it's going to be doubly not possible (or, pedantically, just as impossible) in managed code.
Some alternatives I'd recommend looking into if über performance is not a constraint would be some sort of serialization library. You can get some crazy things done with something like Google's protobuf, eliminating p/invoke and compatibility concerns, etc. if you want to focus on rapid development and consistency. There are also ways to generate C# and C/C++ source code with the relevant structures via a script ranging from a hack-it-yourself C/Python/Perl script to generate a struct for C and C# to complete projects that focus on creating source code from language-agnostic struct definitions, but that's probably outside the scope of this answer.
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I am receiving data via UDP from a C/C++ application. This application is doing a memcpy of the class into a buffer and throwing it our way. Our application is written in C# and I need to somehow make sense of the data. We have access to the header files of the structures - everything is basically a struct or an enum. We can't change the format the data comes in and the header files are likely to change fairly often.
I have considered re-writing our comms classes in C++ to receive the data and then I have more control of its serialisation, but that will take a long time and my C++ is rusty, not to mention I don't have a lot of experience with C++ threading which would be a requirement.
I have also created a few prototype C++ libraries with the provided header files to be accessed via C#, but I can't quite get my head around how I actually create and use an actual instance of the class in C# itself (every time I look into this, all I see are extern function calls, not the use of external types).
I have also looked into Marshalling. However, as the data is liable to change quite often, I think this is a last resort and feels quite manual.
Does anyone know of any options or have any more targeted reading or advice on this matter?
Why not use Google Protocol Buffers on each end i.e. c++ and c#. You would take your c++ definition and let PB do all the serialisation for you.
Protocol buffers are Google's language-neutral, platform-neutral, extensible mechanism for serializing structured data – think XML, but smaller, faster, and simpler. You define how you want your data to be structured once, then you can use special generated source code to easily write and read your structured data to and from a variety of data streams and using a variety of languages. more...
It works across different OSs even where primitive type conversation would normally be a problem.
So here's the background:
We have a legacy program that writes data logs in C++. the data is contained in different structures. The program that reads the log files uses those same structures to display the data. I rewrote the program that reads the log files and C# and had to create C# copy of all those structures by hand.
Is there a better way to do this? I have considered setting up a lookup path to the structures and a sort of parser that would generate a C# structure at build time, but it seems excessively complicated to handle all the special cases. Are there any suggestions to do this? it seems kind of ridiculous that C# doesn't have any backwards compatibility to handle C/C++ structures.
How many structures are there and how complicated are they?
It's a costs vs benefits question I'd say. I'll bet that, judging from your question, just quickly coding the structs in C# is the best way to go.
Just my 2 cents, before taxes...
Summary of your problem:
You have a large number of structs in an existing C++ program that you serialize to disk. You want to port the structs to C# so you can deserialize the data from disk into your C# program. You don't just want to do this once. You want to keep the two sets of structs in sync as both programs evolve.
What you need is an Interface Definition Language (IDL) in which you can describe your data in a language independent way. Something like Apache Thrift, Google Protocol Buffers or MessagePack.
The steps you'd have to take would be:
Convert your existing C++ structs into IDL. This is a one-off process. Use a custom script or look for an existing one. Someone must have solved this by now.
Setup your build system to generate both the C# and the C++ definitions at build time.
Use the Thrift/ProtoBuf/MessagePack C# and C++ APIs to serialize and deserialize your data as needed.
The disadvantages are:
You need build-time code generation. But you already considered this yourself and this way the work has already been done for you.
You will have to change both your C++ and C# to correctly use whatever data structures are generated for you.
The binary on disk format will change so legacy logs won't be readable. But you can write some C++ to convert them to the new format quite easily.
I think this is outweighed by the advantages:
The IDL will contain the canonical description of your data. Any changes to it will be reflected in both your C++ and C#. You won't have to manually update your C# version when the C++ one changes.
The binary data format will be machine-independent. You will be able to read/write your data from many different languages on a variety of platforms.
The third-party libraries I mentioned are robust and widely used. Better than hacking something yourself.
In C its optional. In C++ one "MUST" declare a function before its used/defined. Why is it so? Whats the need? We don't do that in C# or Java.
Funny thing is while we are defining a function. The definition itself has a declaration even then, we need to declare. God knows why?
Funny that you mention that, just this week Eric Lippert wrote a blog post related to your question :
http://blogs.msdn.com/ericlippert/archive/2010/02/04/how-many-passes.aspx
Basically, this is related to how the compiler works. The C# and Java compilers make several passes. If they encounter a call to a method that is not yet known, that's not an error, because the definition might be found later and the call will be resolved at the next pass. Note that my explanation is overly simplistic, I suggest you read Eric Lippert's post for a more complete answer...
Java and C# specify both the language and the binary object file format, and they are multi-pass compilers.
As a result, they are able to peek at later definitions or those that were compiled separately.
C doesn't work this way for several reasons:
Without using managed code it is a lot harder to define a machine-independent object format with type information
C deliberately allows bypassing the type mechanisms
When originally defined, there generally wasn't enough memory to run sophisticated compilers, nor were there prototypes to read anyway
C programs must be arbitrarily large with system-specific library and search path mechanisms. All of this gets in the way of defining an object-module-based type system
Part of the C portability and interoperation basis is the "input language only" nature of the specification
Until recently, even the limited one-pass nature of C was still barely practical for large programs. Something like Java or C# would have been out of the question: you could take a vacation and your make(1) would still not be done
Basically, it's down to how you write the compiler for the language.
In C++, the decision has been to make a one pass compilation possible. To do that, you (or rather the compiler) need to be able to first read the declaration of all classes, methods and the like and then read the implementation (or in C++ terms, the definition). In Java and C#, the compiler first reads through all the code generating what corresponds to what the C++ compiler generates when reading the header files. The C#/Java compiler then reads the implementation (aka definition). So, in C++, the developer is asked to write the declaration whereas in C#, the compiler runs through the code multiple times doing the declaration work for the developer.
As an aside, other languages used to ask you to write the functions in the order you needed them (if function B uses function A, you have to define A first). Most of those languages had constructs to allow you to get around this. In (Turbo) Pascal, the solution was, in a kind, the same as in C++.
C++ vs. Java/C# - Single-pass compiler (C++) vs. multi-pass compiler (Java & C#). Multiple passes allow Java and C# compilers to peek at future types and functions prototypes.
C++ vs. C - The C feature to have default declaration is basically a bug, fixed in C++. It causes problems, and it is an enabled warning for gcc. In C++ the arguments form part of the function exported name (name-mangling), so must be known before the correct function can be called.
In C++ one "MUST" declare a function before its used/defined. Why is it so? Whats the need? We don't do that in C# or Java.
I would like to say, that is not true. Yes, in C++ you have to define a function signature (prototype), before referring to it. But you may leave the implementation for a later time.
In Java that does not work: you cannot call the method of some class without having that class compiled (note: together with implementation) and available in javac classpath. So, Java is more strict in this sense.
Is C++/CLI faster than C#? In which type of operations is it faster?
Not necessarily. However, C++/CLI takes away much of the syntactic sugar around non-performant ways of doing things that is present in C# (boxing for example).
Also, C++/CLI allows you a much more clean interop with unmanaged code, actually allowing you to mix managed / unmanaged code, which is a performance crucial environment may be of benifit.
EDIT:
See this post for some of the differences: http://msdn.microsoft.com/en-us/library/ms379617(VS.80).aspx
Since they both run on the .NET framework, I'd say any performance difference would be negligable. Any difference will almost certainly be down to how well whichever compilers you are using work.
Well, the short answer is no. Why? Reference types in C++/CLI are compiled to MSIL, same as in C#.
The nice thing about C++/CLI (and the long answer) though, is that you can easily call into native code, which (in many cases) is faster. That being said, if you write a native C++ class and expect it to be executed natively when called by someone in a managed class, that native C++ class must be compiled without CLR support (this question goes into how to do that).
Any managed code written in C++/CLI will essentially be exactly the same as the equivalent C#, assuming compiler accuracy, as they'll both end up as intermediate language instructions. However, C++/CLI makes it easy to mix unmanaged code in with the managed portion which may provide considerable speed benefits if well optimised.
Seeing as they are both .NET languages that get compiled into the same byte code that in turn gets run on the same virtual machine I'd say in general, no.
C++/CLI is really only intended to provide language interop between .NET and C++.
Yes, because except few details you can use .net like any other lib while you continue to have the power of c++. Mixing c++ classes with .net classes, inline assembly, create a driver if you want, ect. In c# you can use usafe code but you can't access direct2d api for example, it is limited.
Direct2dTest::MyForm^ form = gcnew Direct2dTest::MyForm();
//use (HWND)form.Handle.ToPointer() to acces the hwnd;
form->Show();
//you can use
//System::Windows::Forms::Application::Run(form);
//or a classic win32 loop
while (GetMessage(&msg, NULL, 0, 0)) {
TranslateMessage(&msg);
DispatchMessage(&msg);
}
Alright so I have this C++ image capturing class. I was wondering if I could get some help..I know basic C++ (I have done one intro to c and one intro to c++ class) and I have NO idea how to do this:
I need to use this class (ie create a new c++ project in my solution) and use c# to reference it and use it to save a screenshot of the screen.
When I try to add a new project I dont know which one to choose (win32, mfc, atl, clr, abc, xyz, and so on) .
The image capturing class is here:
http://pastebin.com/m72414ab
I don't know if I need to create .h files or just a .cpp file would do.. like honestly I have no clue where to start lol. I am looking for a solution, but i want to learn in the process so I dont have to ask next time (not to mention that I like c++ so I am gonna continue coding with it)
You cannot easily use C++ classes from C# without knowing some somewhat specialized information about C++/CLI - either rewrite your C++ class in C and use P/Invoke, or find a fully C# solution.
But I'd like to use this c++ class for speed and memory.
I question this, unless you are capturing images thousands of times a second, there's no way choosing C++ would be of any benefit, and it makes your program much more complicated. Stick with C# until you know you need the slight performance boost.
.NET version 2.0 and above include a CopyFromScreen method on the Graphics object. You can create an image, obtain a drawing surface (Graphics) for that, and then copy from the screen into the image.
A quick bit of Googling produced a simple tutorial which demonstrates this using Visual Basic .NET, although it's trivial to port to C#.
This solution results in the same GDI+ calls that your C++ version uses, with the benefit of not having to link in external C++ code (which, as mentioned above, is not straightforward).
It is definitely possible to use C++ constructs from C#, but it does require some dirty tricks. If I remember correctly, last time I tried to do this I used a Managed C++ layer between C++ and C#, and I think this is the most common way to do it. This method worked well, but indeed was unnecessarily complicated.