I would like to port the SpecialK Poker Hand evaluator to R. I think this should be relatively easy using the Rcpp package, but I have no idea where to begin.
The existing tutorials seem to focus on developing new C++ code for use in R. In this case, I have C++ that solves a problem, and I want to use this code in R with minimum hassle. If the code were one, self-contained function, I could compile and link it on the fly with inline, but this doesn't work here.
I guess this question has 2 parts:
Will I need to make any changes to the C++ source to make it compatible with Rcpp?
How do I call this code from R, given that it's not a small,
self-contained function I can compile and link dynamically using
inline?
I am also open to using the Java, python, or objective-C versions of the evaluator, but I don't think those will be easier to link to R.
Have you looked at Rcpp which makes it fairly painfree to combine R and C++?
Lots of packages use it to bring existing C++ code to R. You can also look at questions here under the [rcpp] tag. Fairly extensive documentation in the package, at my site and other places.
Related
I've started long ago to work on a dynamic graph visualizer, editor and algorithm testing platform (graphs with nodes and arcs, not the other kinds).
For the algorithm testing platform i need to let the user write a script or call a script from a file, which will interact with the graph currently loaded. The visualizer would do things like light up nodes while they're being visited by the script algorithm, adding some artificial delay, in order to visualize the algorithm navigating and doing stuff.
Scripts would also be secondly used to add third party features that i could either make available as pre-existing scripts in the program folder OR just integrate inside the program in c++ once they're tested and working.
All my searches for an interpreter to embed in my program sent me to lua;
then i started handwriting my own recursive descent parser for my own C-like syntax scripting language (which i planned to use a subset of C++ grammar so that any code written in my scripting language can be copy-pasted in any C++ code.
It was an interesting crazy idea which i don't regret at all, I have scopes, functions, cycles, gotos, typesafe variables, expressions.
But now that i'm approaching the addition of classes, class methods, inheritance (some default classes would be necessary to interface scripts to the program), i realized it's going to take A LOT of time and effort. A bit too much for a personal project of an ungraduated student with exams to study for… but still i whish to complete this project.
The self-imposed requirement of the scripts being 100% compatible with C++ was all but necessary, it would have been just a little nice extra thing, which i can do without.
Now the question is, is there an alternative to lua with a c-like syntax that supports all i've already done plus classes and inheritance? (being able to add custom "classes" that interface scripts to the program is mandatory)
(i can't assume the user to have a full c++ compiler installed so i cant just compile their "script" at runtime as a dll to load and call it, although i whish i could)
Just-in-time compilation of C++
Parsing C++ is hard. Heck, parsing C is hard. It's difficult to get it right, and there are a lot of edge cases. Thankfully, there are a few libraries out there which can take code and even compile it for you.
libclang
libclang provides a lot of facilities for parsing c++. It's a good, clean library, and it'll parse anything the clang compiler itself will parse. This article here is a good starter
libclang provides a JIT compilation tool that allows you to write and compile C++ at runtime. See this blog post here for a overview of what it does and how to use it. It's very general, very powerful, and user-written code should be fast.
GCC also provides a library called libgccjit for just-in-time compilation during the runtime of a program. libgccjit is a C library, but there's also a C++ wrapper provided by the library maintainers. It can compile abstract syntax trees and link them at runtime, although it's still in Alpha mode.
cppast
If you don't want to use libclang, there's also a library under development called cppast, which is a C++ parser which will give you an abstract syntax tree representation of your c++ code. Unfortunately, it won't parse function bodies.
Other tools
If anyone knows any other libraries for compiling or interpreting C++ at runtime, I encourage them to update this post, or comment them so I can update it!
Here is something that lets you embed a C-like scripting language in your application (and a bunch of other cool things):
http://chaiscript.com/
There is lots of documentation:
https://codedocs.xyz/ChaiScript/ChaiScript/
I am new to C++, with some training using fortran95. Trying to convert my knowledge into the new syntax but have run into a snag.
Many of my programs use modules with subroutines, and subroutines within subroutines and use of functions from a library described by NAG.com which are readily available and searchable.
I am currently looking for a c++ version of
http://www.nag.com/numeric/FL/manual/pdf/F08/f08naf.pdf
From what I have read so far, these libraries exist for c++ and I have used some simple ones thus far(like vector, cmath, math.h) but only ones that are already included in my Xcode package for my mac.
I haven't seen anybody mention one of these which my be included with my Xcode, and I am lacking in how to implement outside libraries I find. I am interested particularly in using:
http://www.alglib.net/download.php
Thus far I have been using subrutines as void type functions and simply including them in all of my code. But my code is becoming exceedingly cumbersome and I would like to make something similar to a fortran module to do chebyshev calculations. And I would much rather find a good library of eignevalue calculators and maybe even chebyshev calculators, . . . which I can use.
Essentially my question is, how do I implement external libraries I find and does anybody have a recommendation for a good one? How can I make my own code which contains a callable set of functions and then call it from within another piece of code?
If I understand right, the part of the NAG library you're using in Fortran is basically LAPACK. There is a C interface to LAPACK, called LAPACKE (http://www.netlib.org/lapack/lapacke.html). You can use it in a C++ program.
I didn't understand the other parts of your question.
I can't find any documentation about how to use the "forecast" R package from C++. Is anything available online?
I have not looked closely but as it depends on the CRAN packages Rcpp and RcppArmadillo (which I am involved and which facilitate C++ use from R), I'd say yes. You can probably poke around in the sources and find other entry points. It's open source, after all.
But if you asked for a well-defined pre-existing API for forecast, the answer may be no.
Edit: Oh, and the obvious plug for RInside which allows you to embed [a single instance of] R very easily inside your C++ application. It does this by wrapping the existing (but hard to use) embedding API in a much simpler to use C++ class which abstracts away all the handholding.
I have a demo application that is written in Python. It uses a lot of existing C++ code (written by me) that relies on OpenCV for image processing. Currently, communication between Python and C++ is being done through file I/O and subprocess calls, which isn't very efficient. What is the best way to wrap the C++ code so that it can be called from Python?
There is too much C++ code to think about porting it to Python, so that's not really an option.
A long time ago, the Python OpenCV wrappers were written in SWIG, but it looks like the most recent version of the wrappers is completely different. Can anyone point me in the right direction?
There are two ways that you can make your python program interact directly with your C/C++ program:
Wrap your C/C++ code in a DLL with C-API only. Then, use ctypes
to call C-function within the DLL. The advantage of this way is that you don't need to include/link any other library.
Extend python by adding new python module. You may use boost python to easily create a python module. The advantage of this way is that you don't need to wrap your code to C-API.
Without knowing code complexity, variety of C++ code and style of it... I would recommend "Extending Python"
It's not an immediate solution (you should change the C++ code, prototype some new functions or add a simple wrapper layer in C). But, if you plan to do a complex project (and are also a bit worried on performance)... it seems the best way to do it.
Porting C++ code to Python seems a step backwards, doing new code in Python is ok (I'm a fan of it) but C++ will (often) be more efficient.
Edit: Take also a look on ctypes module. Maybe it suits your needs. If you are more comfortable doing the wrapping in python language, then it may be better. If you don't mind playing with the C code, then extend Python by doing a module with your existing code.
I recently asked this question https://softwareengineering.stackexchange.com/questions/129076/go-instead-of-c-c-with-cgo and got some very interesting input. However there's a mistake in my question: I assumed cgo could also be used to access c++ code but that's not possible. Instead you need to use SWIG.
The go faq says "The cgo program provides the mechanism for a “foreign function interface” to allow safe calling of C libraries from Go code. SWIG extends this capability to C++ libraries. "
my question:
Is it possible to access high-level c++ frameworks such as QT with SWIG + Go and get productive? I'd like to use Go as a "scripting language" to utilize c++ libraries.
Have you any experience with go and swig? Are there pitfalls I have to be aware of?
Update/Answer: I've asked this over IRC too and I think the question is solved:
SWIG is a rather clean way of interfacing c++ code from other languages. Sadly matching the types of c++ to something like go can be very complex and in most cases you have to specify the mapping yourself. That means that SWIG is a good way to leverage an existing codebase to reuse already written algorithms. However mapping a library like Qt to go will take you ages. Mind it's surely possible but you don't want to do it.
Those of you that came here for gui programming with go might want try go-gtk or the go version of wxWidgets.
Is it possible? Yes.
Can it be done in a reasonably short period of time? No.
If you go back and look at other projects that have taken large frameworks and tried to put an abstraction layer on it, you'll find most are "incomplete". You can probably make a fairly good start and get some initial wrappers in place, but generally even the work to get the simple cases solved takes time when there is a lot of underlying code to wrap, even with automated tools (which help, but are never a complete solution). And then... you get to the nasty remaining 10% that will take you forever (ok, a really really long time at least). And then think about how it's a changing target in the first place. Qt, for example, is about to release the next major rewrite.
Generally, it's safest to stick to the framework language that the framework was designed for. Though many have language extensions within the project itself. For example, for Qt you should check out QML, which provides (among many other things) a javascript binding to Qt. Sort of. But it might meet your "scripting" requirement.
A relevant update on this issue: it is now possible to interact with C++ using cgo with this CL, which is merged for Go 1.2. It is limited, however, to C-like functions calls, and classes, methods and C++ goodies are not supported (yet, I hope).