I am writing code to parse a complicated string in C++ and create a tree from it. I would like to use C# in Visual Studio 2017 to call a native c++ method that returns a vector of nodes.
A Node looks like:
class node
{
public:
std::vector<node> subnodes;
std::string name;
};
and the c++ function might look like:
class noderizer
{
public:
node getNodes(std::string str);
};
what is the most efficient (coding time with secondary consideration for speed) way to call the noderizer::getNodes(...) member and create a equivalent class for c#?
I am assuming that the best route is to create a duplicate class definition in c# and then copy marshal the native std::strings into managed Strings"
public class node
{
public string name = string.Empty;
List<node> integers = new List<node>();
}
It's not clear if this article contains the latest information for c++ interop, but a related article on wrapping c++ native classes for use in c# indicates that I could most likely just wrap noderizer native c++ as noderizer * m_Impl; and then call the getNodes member and copy over each parameter. Is this the correct methodology?
You could use pInvoke as per your first referenced article, but the objects you are returning seem quite complicated. I think you will have a heck of a time with data marshalling if you're not already well versed (and even then). pInvoke is great for simple calls to C libraries where data marshalling is basic, but it gets very complicated very fast. This is not good for your situation.
The second article is closer to where you want to look. That being said, you have to consider whether you want to be wrapping a managed class or just calling a function that takes a string and returns your tree in managed format (i.e. it makes a copy rather than wrap unmanaged data). By your post it seems like you just need the latter.
Your best option is to use C++/CLI. Check out this tutorial. I am confident that taking this approach will make light work of your task. I won't attempt to explain the subject as the article above does a very good job. In essence, you will be able write functions with both managed and unmanaged data types, where all the data marshalling is built into the environment. A simple cast will marshal the data for you behind the scenes. As a big bonus, debugging is great as you can step from C# to C++/CLI to C++ code and back.
In the article above, the author does describe how to wrap an unmanaged class, which you can well do, but your problem will still be with data conversion.
I would approach your problem in 4 steps:
Write a static function getNodes() in C++/CLI that you can call from C# as any regular static method, passing a string as an argument. The article above will help you with that. Also See Here when creating the C++/CLI project.
getNodes() will use your C++ code to create a tree in its unmanaged form.
Use getNodes() to convert the tree from unmanaged to managed form.
Return the result to the caller in C#.
your declaration will look something like this, where the Node is your managed calss, ref keyword signifies that the class is managed, and ^ is the managed version of *.
public ref class noderizer
{
public:
static Node^ getNodes(String ^mStr);
};
Here getNodes() calls your C++ function and does the data conversion. I don't think it will take you long to figure it out.
Once you get a hang of the syntax, I think you will find it quite intuitive to use if you are already familiar with C# and C++.
As for performance, unless you're making thousands of consecutive calls or need critical real time data, it should not be an issue. One thing I would say though, if you're concerned with performance, you should write the pure C++ code in a separate purely unmanaged dll. I can't find the article for the life of me, but I remember looking at some benchmarks of executing purely unmanaged long running code block that was compiled inside the C++/CLI dll vs calling the exact same code that was compiled inside its own purely unmanaged dll. If I recall correctly, the separate dll was something like 3x faster.
This question already has answers here:
What is the best scripting language to embed in a C# desktop application? [closed]
(15 answers)
Closed 6 years ago.
I have a C# program that uses objects from a class that has a method looking something like this:
public double TheMethod(double argument1, double argument2, ...,double argumentN)
{
//method body: do something with the arguments
//return the result
}
I would like to give the user the ability to write their own logic into the method body and then have that be used when the program is run.
It seems to me that scripting may be the way to go, but I am having trouble trying to get started. What is the best way to approach this situation?
Note: If it matters, the program would be run from within a larger main desktop application. I would like the user to be able to write their code when the application is already running through some sort of editor program. Their code would then be saved and used once they launch the program that actually uses the method.
You can certainly dynamically compile and execute C#. See Is it possible to dynamically compile and execute C# code fragments?
Depending on who your users are and how their script needs to integrate into the wider application, IronPython might be a nicer option - essentially scripting in python. See https://blogs.msdn.microsoft.com/charlie/2009/10/25/running-ironpython-scripts-from-a-c-4-0-program/ for details on integrating C# and IronPython.
As always when running any dynamically injected code from an external source, think about security.
If you want your users to write in c#, the simplest thing would probably be to swap out the file (or at least the body of the method) with different copies and recompile the sub-application before each run.
It is possible to do a live replace of a method body during run-time, but it's not for the light hearted! https://msdn.microsoft.com/en-us/library/system.reflection.emit.aspx
If you are happy to do the work to create your own mini scripting language, take a look at Antlr http://www.antlr.org/
What is the easiest way to get an abstract-syntax-tree within C# from a Lua script? I'm trying to do a simple static code analysis within C# for a Lua script.
Many existing code analysis tools like LuaInspect are based on MetaLua, but I don't see an easy way to integrate MetaLua within C#. And projects like Lua for Irony seem to be in an alpha stage or the development has stopped years ago.
What would be your suggestion to get an AST for LUA within C# for static code analysis?
You might want to try monosharp: http://www.moonsharp.org/
It uses ANTLR to build a C# AST. You will probably have to do some code spelunking though, since its main objective isn't "creating an AST" but actually "interpreting Lua directly in C#".
If you can run Lua code, nothing should stop you from integrating LuaInspect and MetaLua. The earlier versions of MetaLua required some manual work to avoid compilation steps, but the recent versions (0.7+) don't require much work. The generation of AST is as simple as:
require('metalua.compiler').new():src_to_ast(src, filename)
Note that LuaInspect hasn't been updated to support lineinfo format changes in the recent metalua versions, so if you plan on using it with ML 0.7+, you may review these changes I made to make it work in the Lua IDE I'm working on.
Is there a way of compiling C# code in C? I can do it in C#, but I'm not sure about how to do it, if you even can do it in C. Thanks :)
Note: Preferably C# (.NET)
You can load CLR into your process (it's a COM component), create the needed objects/interfaces from Sytem.CodeDOM namespace and use them. But that's tedious, and I wouldn't recommend it.
Just call csc.exe from your program.
No I dont think thats possible unless you are trying to prepare some compilers.
C# code will be executed under CLR( Common Language Runtime Engine) hence it is called ManagedCode. CLR creates proper execution environment for C# code to run properly. C Code is called UnManaged Code as it does not run under CLR. hence C# code can not be compiled in C.
I have a small to medium project that is in C++/CLI. I really hate the syntax extensions of C++/CLI and I would prefer to work in C#. Is there a tool that does a decent job of translating one to the other?
EDIT: When I said Managed c++ before I apparently meant c++/CLI
You can only translate Managed C++ code (and C++/CLI code) to C# if the C++ code is pure managed. If it is not -- i.e. if there is native code included in the sources -- tools like .NET Reflector won't be able to translate the code for you.
If you do have native C++ code mixed in, then I'd recommend trying to move the native code into a separate DLL, replace your calls to DLL functions by easily identifiable stub functions, compile your project as a pure .NET library, then use .NET reflector to de-compile into C# code. Then you can replace the calls to the stub functions by p-invoke calls to your native DLL.
Good luck! I feel for you!
.NET Managed C++ is like a train wreck. But have you looked into C++ CLI? I think Microsoft did a great job in this field to make C++ a first class .NET citizen.
http://msdn.microsoft.com/en-us/magazine/cc163852.aspx
I'm not sure if this will work, but try using .Net Reflector along with ReflectionEmitLanguage plug-in. The RelelectionEmitLanguage plug-in claims to convert your assembly to c# code.
It has to be done manually unfortunately, but if the code is mostly C++/CLI (not native C++) then it can actually be done pretty quickly. I managed to port around 250,000 lines of C++/CLI code into C# in less than a couple of months, and I don't even know C++ very well at all.
If preserving Git history is important, you might want to git mv your cpp file into a cs file, commit, then start porting. The reason for this is that Git will think your file is new if you modify it too much after renaming it.
This was my approach when porting large amounts of code (so that it wouldn't take forever):
Create another worktree / clone of the branch and keep it open at all times
This is extremely important as you will want to compare your C# to the old C++/CLI code
Rename cpp to cs, delete header file, commit
I chose to rename the cpp file since its git history is probably more important than the header file
Create namespace + class in cs file, add any base classes/interfaces (if abstract sealed, make static in C#)
Copy fields first, then constructors, then properties, and finally functions
Start replacing with Ctrl+H:
^ to empty
:: to .
-> to .
nullptr to null
for each to foreach
gcnew to new
L" to "
Turn on case sensitivity to avoid accidental renames (for example L"cool" should become "cool", not "coo"
Prefixes like ClassName:: to empty, so that MyClass::MyMethod becomes MyMethod
Go through the red code and port manually code that cannot be just replaced (e.g. some special C++ casts), unless you have some cool regex to do it fast
Once code compiles, go through it again, compare to C++/CLI line by line, check for errors, clean it up, move on.
If you encounter a dependency that needs to be ported, you could pause, port that, then come back. I did that, but it might not be so easy.
Properties were the most annoying to port, because I had to remove everything before and after the getters and setters. I could have maybe written a regex for it but didn't bother doing so.
Once the porting is done, it's very important that you go through the changes line by line, read the code, and compare with C++/CLI code and fix possible errors.
One problem with this approach is that you can introduce bugs in variable declarations, because in C++/CLI you can declare variables in 2 ways:
MyType^ variable; <- null
MyType variable; <- calls default constructor
In the latter case, you want to actually do MyType variable = new MyType(); but since you already removed all the ^ you have to just manually check and test which one is correct. You could of course just replace all ^'s manually, but for me it would have taken too long (plus laziness) so I just did it this way.
Other recommendations:
Have a dummy C++/CLI project and a tool like LinqPad or another C# project to test differences between C++/CLI and C# if you're unsure of a piece of ported code
Install Match Margin to help highlight similar code (helped me when porting WinForms code)
ReSharper! It helped with finding bugs and cleaning up the code a LOT. Truly worth the money.
Some gotchas that I encountered while porting:
Base classes can be called in C++/CLI like so: BaseClass->DoStuff, but in C# you would have to do base.DoStuff instead.
C++/CLI allows such statements: if (foo), but in C# this has to be explicit. In the case of integers, it would be if (foo != 0) or for objects if (foo != null).
Events in base classes can be invoked in C++/CLI, but in C# it's not possible. The solution is to create a method, like OnSomeEvent, in the base class, and inside that to invoke the event.
C++/CLI automatically generates null checks for event invocations, so in C# make sure to add an explicit null check: MyEvent?.Invoke(this, EventArgs.Empty);. Notice the question mark.
dynamic_cast is equivalent to as cast in C#, the rest can be direct casts ((int) something).
gcnew can be done without parentheses. In C# you must have them with new.
Pay attention to virtual override keywords in the header files, you can easily forget to mark the C# methods with override keyword.
Intefaces can have implementations! In this case, you might have to rethink the architecture a bit. One option is to pull the implementation into an abstract class and derive from it
Careful when replacing casts with Convert calls in C#
Convert.ToInt32 rounds to the narest int, but casting always rounds down, so in this case we should not use the converter.
Always try casting first, and if that doesn't work, use the Convert class.
Variables in C++/CLI can be re-declared in a local scope, but in C# you get naming conflicts. Code like this easily lead to hard to find bugs if not ported carefully.
Example: An event handler can take a parameter e, but also has a try-catch like catch (Exception e) which means there are 2 e variables.
Another example:
// number is 2
int number = 2;
for (int number = 0; number < 5; number++)
{
// number is now 0, and goes up to 4
}
// number is again 2!
The above code is illegal in C#, because there is a naming conflict. Find out exactly how the code works in C++ and port it with the exact same logic, and obviously use different variable names.
In C++/CLI, it's possible to just write throw; which would create a generic C++ exception SEHException. Just replace it with a proper exception.
Be careful when porting code that uses the reference % sign, that usually means that you will have to use ref or out keywords in C#.
Similarly, pay attention to pointers * and & references. You might have to write additional code to write changes back whereas in C++ you can just modify the data pointed to by the pointer.
It's possible to call methods on null object instances in C++/CLI. Yes seriously. So inside the function you could do If (this == null) { return; }.
Port this type of code carefully. You might have to create an extension method that wraps over this type of method in order to avoid breaking the code.
Check and make sure everything in the old project file vcxproj was ported correctly. Did you miss any embedded resources?
Careful when porting directives like #ifdef, the "if not" (#ifndef) looks awfully similar but can have disastrous consequences.
C++/CLI classes automatically implement IDisposable when adding a destructor, so in C# you'll need to either implement that interface or override the Dispose method if it's available in the base class.
Other tips:
If you need to call Win32 functions, just use P/Invoke instead of creating a C++/CLI wrapper
For complex native C++ code, better create a C++/CLI project with managed wrappers
Again, pay attention to pointers. I had forgotten to do Marshal.StructureToPtr in my P/Invoke code which wasn't necessary in the C++ version since we had the actual pointer and not a copy of its data.
I have surely missed some things, but hopefully these tips will be of some help to people who are demoralized by the amount of code that needs to be ported, especially in a short period of time :)
After porting is done, use VS/ReSharper to refactor and clean up the code. Not only is it nice for readability, which is my top priority when writing code, but it also forces you to interact with the code and possibly find bugs that you otherwise would have missed.
Oh and one final FYI that could save you headaches: If you create a C++/CLI wrapper that exposes the native C++ pointer, and need to use that pointer in an external C++/CLI assembly, you MUST make the native type public by using #pragma make_public or else you'll get linker errors:
// put this at the top of the wrapper class, after includes
#pragma make_public(SomeNamespace::NativeCppClass)
If you find a bug in the C++/CLI code, keep it. You want to port the code, not fix the code, so keep things in scope!
For those wondering, we got maybe around 10 regressions after the port. Half were mistakes because I was already on autopilot mode and didn't pay attention to what I was doing.
Happy porting!
Back ~2004 Microsoft did have a tool that would convert managed C++ to C++/CLI ... sort of. We ran it on a couple of projects, but to be honest the amount of work left cleaning up the project was no less than the amount of work it would have been to do the conversion by hand in the first place. I don't think the tool ever made it out into a public release though (maybe for this reason).
I don't know which version of Visual Studio you are using, but we have managed C++ code that will not compile with Visual Studio 2005/2008 using the /clr:oldSyntax switch and we still have a relic VS 2003 around for it.
I don't know of any way of going from C++ to C# in a useful way ... you could try round tripping it through reflector :)
Such projects are often done in c++/cli because C# isn't really an elegant option for the task. e.g. if you have to interface with some native C++ libraries, or do very high performance stuff in low level C. So just make sure whoever chose c++/cli didn't have a good reason to do it before doing the switch.
Having said that, I'm highly skeptical there's something that does what you ask, for the simple reason that not all C++/cli code is translatable to C# (and probably vice versa too).