I have the following question:
Let's assume I have many different C++ libraries(algorithms), which are written in the same style . (They need some inputs and give back some outputs).
I've done some research and wanted to ask if its possible to auto-generate Wrapper classes (by using an algorithm which are given the input and the outputs of the c++ algorithm), which can be easily used in Objective-C/Java (iOS/Android) then .
The app-programming part isn't really time-consuming.
You'll want to look at SWIG. This generates bindings for other languages from a C based API. Objective-C support is in there as is Java.
I'm not sure what happened to objective-C support in the later versions, but its in v1.1 and you can see the branch where it was added.
Related
Let's say i have a huge lib in C++ (with tons of dependencies, it needs about 3h for a full build under GCC). I want to build upon that lib but don't want to do so in C++ but rather in a more productive language. How can i actually bridge or wrap that extern lib package so i can access it in another language and program on top of it?
Languages considered:
Swift
Go
What i found is, that both languages do provide auto bridging or wrapping for C libs and code (I don't actually know whats the difference between wrapping / bridging). So, if i have some c code, i can just throw it in the same Swift or Go project and can use it with a simple import in my project.
This doesn't work in both languages for C++ code however. So i googled how to transform C++ libs to C code or generate autowrappers. I found the following:
swig.org - auto wrapper for C++ libs
Comeau C++ compiler - automatically transfers C++ to C code
LLVM - should be able to take any input and transform it to any output that LLVM is capable of.
Question:
Is it even in the realms of usable / realistic / managable to build
on top of such a huge lib in other languages like Swift / Go, if
using auto wrapping or auto bridging?
What of the 3 listed libs / programs / frameworks works best for the process of C++ -> C (because Swift and Go both provide C auto
wrapping).
Are there better alternatives than what i considered so far?
Would it be better to just "stick with C++" as using any other tools to do the wrapping / bridging process would be far to much
work to equal out the benefit of using a more productive language
like Swift / Go?
Thanks:)
Disclaimer: There is also the possibility to manually wrap a C++ lib in C but that would take an unbearable amount of work for such a huge lib.
Q1: Is it realistic?
Not realistic, because any large complicated C++ interop is going to get too complicated. Automatic tools are likely to fail and manual work is too hard.
Q2: What's best?
I don't know and given A1 it does not seem to matter.
Q3: Alternative?
Q4: Is C++ only the best alternative?
If you want to take advantage of existing C++ code from another language regardless of the language involved the best option in complex scenarios is to use a hybrid approach.
Most languages provide interop to C and not C++ due to non-standard C++ naming convention. In other words, just about every language provides access to plain C-functions, but C++ is frequently not supported.
Since your library is complex, the best solution would be based on "Facade" pattern. Create a new C-library and implement application specific logic that utilizes C++ library. Try to design this library to be as thin as possible. The goal is not to write all business logic, but to provide C-functions that hold on C++ objects and call C++ functions. The GO-level language code would then call this library to use C++ library underneath. This approach differs from Q1 approach. In Q1 you attempt to have one interop call on per C++ function or object's method. In Facade you attempt to implement C++ usage scenarios that are unique to your application.
With Facade you reduce the scope of interop work, because you target your application scenarios. At the same time you mitigate away from C++ complexity at GO language level.
For example, you need to read a temperature sensor using C++ library.
In C++ you'd have to do:
open file
read stream until you find SLIP terminator
read one "record"
close file
With facade you create a single function called "readTemperature(deviceFileName)" and that C function executes 4 calls at once.
That's a fake example, just to show the point.
With facade you might want to hide original C++ objects and at this point it becomes a small layer. The goal here is to stay focused and balance your application needs with generalization to support your application.
Interestingly enough Facade approach is a way to improve interop performance. Interop in just about every language is more expensive than normal operations due to need to marshal from langauage runtime environment and keep it protected. Lots of interop calls slow down application (we are talking about millions here). For example, having 10 interop calls combined into 1 improves performance, because amount of itnerop operations is reduced.
I was successful wrapping a large (although perhaps not "huge") C++ library (hundreds of header files) in Swift using a relatively simple process. You directly link your project to the library. The only thing you have to wrap are any new functions that you write (to be invoked in Swift) that actually use the library (in the C++ wrapper file). The verbose stuff can be left in the wrapper file, mostly without any modification. There is a simple little tutorial which helped me: https://www.swiftprogrammer.info/swift_call_cpp.html
(FYI, there is one step he omitted: Set your library search paths in Build Settings => Search Paths => Library Search Paths (both Debug and Release) )
In The Pragmatic Programmer:
Normally, you can simply hide a third-party product behind a
well-defined, abstract interface. In fact , we've always been able to
do so on any project we've worked on. But suppose you couldn't isolate
it that cleanly. What if you had to sprinkle certain statements
liberally throughout the code? Put that requirement in metadata, and
use some automatic mechanism, such as Aspects (see page 39 ) or Perl,
to insert the necessary statements into the code itself.
Here the author is referring to Aspect Oriented Programming and Perl as tools that support "automatic mechanisms" for inserting metadata.
In my mind I envision some type of run-time injection of code. How does Perl allow for "automatic mechanisms" for inserting metadata?
Skip ahead to the section on Code Generators. The author provides a number of examples of processing input files to generate code, including this one:
Another example of melding environments using code generators happens when different programming languages are used in the same application. In order to communicate, each code base will need some information in commondata structures, message formats, and field names, for example. Rather than duplicate this information, use a code generator. Sometimes you can parse the information out of the source files of one language and use it to generate code in a second language. Often, though, it is simpler to express it in a simpler, language-neutral representation and generate the code for both languages, as shown in Figure 3.4 on the following page. Also see the answer to Exercise 13 on page 286 for an example of how to separate the parsing of the flat file representation from code generation.
The answer to Exercise 13 is a set of Perl programs used to generate C and Pascal data structures from a common input file.
I would like to write some pieces of code in Scala . It is important for me that this code can be called from matlab. AFAIK java code can easily be integrated with matlab. http://www.mathworks.co.uk/help/matlab/ref/javamethod.html
Is this valid also for scala code?
It is also valid for Scala code. Just pretend that you're doing Java interop (e.g. a method called + would actually be $plus) and make sure scala-library.jar is in Matlab's classpath (e.g. using javaaddpath).
Incidentally, I've done Java/Matlab interop before, and it's not as "easily integrated" as one might hope. Passing data is kind of awkward and you tend to trip on classloader and/or classpath issues every now and then.
I'd be wary of planning a big project with lots of tightly-connected interop. In my experience it usually works better using the Unix mindset: make independent tools that do their own thing well, and chain them together to get what you want. For instance, I routinely have Scala write Matlab code and call Matlab to run it, or have Matlab use system to fire up a Scala program to process a subset of the data.
So--calling Scala from Matlab is completely possible, and for simple interfaces looks just like Java. Just try to keep the interface simple.
You could encapsulate your Scala code in another language that's easily called by Matlab, such as Java of C. Since you seem to know about Java, you could use these examples to learn to encapsulate your Scala methods inside Jave methods that you can call from Matlab. A number of other methods are available to you with different languages (MEX-files, loadlibrary, etc...)
I'm just thinking of porting some old C++ sources held in my archive to iOS thus supplying a ObjC GUI, using wrappers for some C++ stuff and leave the important data working stuff within the C++ code. So, the problem is that the old sources come from Win32 MFC thus using CString class for strings and I want to replace that with Joe O'Leary's CStdString which is a C++ template class that will do it just fine ... but:
I have to use the string class definition along with a big bunch of different C++ sources and so each of them will include the CStdString template on their own. Normally I would write a wrapper for the whole string class, but better if I needn't.
Will I have a problem with instantiation of strings in the different sources? Could it make a problem to pass a templated string from one source to another? In fact I don't know if the compiler generates the code for a template only once or multiple times having the fact that the same instantiation type is used for the template.
Can you fill some light into this?
Thanks...
MFC and CString may only work properly on Windows OS so they aren't good candidates to be putting in any kind of library that will be potentially used by a platform other than windows.
I'm not familiar with Joe O'Leary's CStdString classes but I'd recommend using std::string as much as possible and char* with "extern C" exports and wrapping functions for use outside of C++ land as the c-style string is more easily compatible with other languages that may need to call into your C++ library.
As far as templates all the variations are generated at compile time and then the correct implementation is chosen at run time as far as I know. However your problem will most likely be in translation from one kind of string to another which may require you to create some middle layer or wrapper to marshal from string type of one language to another.
I agree with CString, as long as you stay with std::string or some other multi-platform string implementation for C++ you are not going to face any issues ( even boost works on iOS ).
I've been integrating C++/Obj-C for about two years now so you can be sure that keeping model classes in C++ ( even with heavily templated code ), is not a problem. I would advice you to do what you could do best with Obj-C in Obj-C though... ( avoiding being a hammer developer :) )
Good luck!
I am doing a compilers discipline at college and we must generate code for our invented language to any platform we want to. I think the simplest case is generating code for the Java JVM or .NET CLR. Any suggestion which one to choose, and which APIs out there can help me on this task? I already have all the semantic analysis done, just need to generate code for a given program.
Thank you
From what I know, on higher level, two VMs are actually quite similar: both are classic stack-based machines, with largely high-level operations (e.g. virtual method dispatch is an opcode). That said, CLR lets you get down to the metal if you want, as it has raw data pointers with arithmetic, raw function pointers, unions etc. It also has proper tailcalls. So, if the implementation of language needs any of the above (e.g. Scheme spec mandates tailcalls), or if it is significantly advantaged by having those features, then you would probably want to go the CLR way.
The other advantage there is that you get a stock API to emit bytecode there - System.Reflection.Emit - even though it is somewhat limited for full-fledged compiler scenarios, it is still generally enough for a simple compiler.
With JVM, two main advantages you get are better portability, and the fact that bytecode itself is arguably simpler (because of less features).
Another option that i came across what a library called run sharp that can generate the MSIL code in runtime using emit. But in a nicer more user friendly way that is more like c#. The latest version of the library can be found here.
http://code.google.com/p/runsharp/
In .NET you can use the Reflection.Emit Namespace to generate MSIL code.
See the msdn link: http://msdn.microsoft.com/en-us/library/3y322t50.aspx