I want to use some C++ STL collections in my Objective-C iPhone app. Apparently this is possible by giving files the extension ".mm" . What are some of the quirks/surprises associated with this?
I want to use the basic containers that I'm familiar with (vector, queue, set, ...)
Cheers!
See Using C++ With Objective-C for a detailed list of what you can and can't do. You can do most things that you would expect. You just can't do things like have a C++ class inherit from an Objective-C class or vice-versa, you can't mix C++ exceptions with Objective-C exceptions, and C++ introduces several new keywords not present in Objective-C.
The major quirk of Objective-C++ is that if you don't pass -fobjc-call-cxx-cdtors to g++, it won't call the constructor and destructor of C++ instance variables in of ObjC objects. So remember to turn that option on and you should be good.
The files will be compiled with the Objective-C++ compiler, so things will behave more like g++ than gcc, but since that's what you want it probably doesn't count as a surprise. From the Objective-C side, I'm not aware of any gotchas, and I've worked on several large projects that made significant used of Objective-C++. Just keep in mind that Objective-C reserved words are reserved in Objective-C++ as well, so you can occasionally run into issues with third-party C++ libraries (e.g., if they use "id" as a parameter in a public interface).
You'd be surprised how well it works. I haven't really gotten into any problems intermixing Obj-C and C++ in a .mm file.
Related
What are the methods of developing for iOS with C++? I am familiar with using Objective-C++ within Xcode, by selecting Obj-C as my language when creating a new project, but what else is there. I know there are tools like Xamarin that allow for iOS development in C#, however i'm curious as to what officially supported ways of developing for iOS in C++ there are? Can an iOS app be written completely in C++ with no Objective-C and compile?
I have an app that pretty freely intermingles Objective-C (.mm files), Objective-C++ (.m files), and C++ (.cpp) as needed. The C++ code is legacy functionality that implements the heavy lifting of our app and has worked across a number of platforms for 20+ years. No need to re-implement that.
To write a C++ object in XCode, just do it. Create .cpp and .h files like you would anywhere else.
When you need to interact with a C++ object from Objective-C, you can either go into the properties of the .m file in XCode and change it to use the Objective-C++ compiler, or (better yet) just name it .mm instead of .m. Then you can include your C++ header files with standard #include statements, create C++ objects with new, delete them with delete, and access members with dot notation and pointer notation just like you would from C++.
Objective-C is a lot easier to use when dealing with the UI and system calls. It isn't hard to learn. There are probably ways to access all of those objects and methods from C++, but the gymnastics you would have to do each time might make it easier to simply learn enough Objective-C (or Swift) to do those parts in the language Apple intended. (Keep in mind that to figure out how to do everything in C++ while looking at sample code and documentation that assumes Objective-C or Swift, you're going to have to master those languages anyway.)
Yes, you can even go to extreme lengths to avoiding Objective-C, you won't be able to do so completely since UIKit depends on it, but nearly every other framework has a C API. Take a look at this question and the answer to it How to write iOS app purely in C
C is not C++, but the answer will give you a hint on what you can do. It will involve including the objc runtime, and using objc_msgsend.
Here is the scenario:
My swift app collects data from bluetooth and should process them in real-time. These data comes mainly from IMU(gyroscope, magnetometer and accelerometer).
Algorithms that process all of that is going to be written in c++ and utilize some libraries like Eigen. How should I approach such problem? From what I've found:
1) put c++ files into my project, write wrapper in objective-c and bridge it to Swift. Also now sure if I can include Eigen in mobile app easily. This would be tedious process I suppose
2) Get all algorithms as library( .dll, .lib and call it directly from swift, not sure if it's possible)
3) Rewrite all algorithms to Swift, utilize Eigen substitute for Swift, not sure if anything like this exist. Also, this solution is less efficient and would probably fail because of deadlines.
How should I approach such problem? How to solve it in a most efficient way, where I can make use of already exisiting c++ code?
I believe some of you would see this question as opinion based, but I do not know how to state this problem in a way that excludes any ambiguity.
How to run c++ files that uses Eigen in iOS app written is Swift?
Thanks in advance
You cannot call c++ from Swift. However, you can call c++ from objective-c++. And you can call objective-c++ from both Swift and objective-c.
Just make sure that your public-facing #interface code (in the .h file) contains only objective-c. (no classes, no templates, no namespaces, no including c++ headers).
Your #implementation goes in a file with extension .mm which will compile as objective-c++ - giving you an objective-c interface with the full use of c++ in the implementation of the Objective-C object.
c++ objects live quite happily as the member variables of an objective-c++ implementation. However, they will be default-constructed then the objc runtime calls Init. If you are using objects which don't have default constructors, you will need to either wrap them in a boost::optional or a std::unique_ptr (etc).
You can them import the objective-c objects into your Swift program.
Full example for anyone who has not done this before:
https://github.com/madmongo1/swift-to-cpp-demo.git
As the title says... are they considered different languages? For example if you've written an application using a combination of C++ and Objective-C++ would you consider it to have been written in C++ and Objective-C, C++ and Objective-C++ or all three?
Obviously C and C++ are different languages even though C++ and C are directly compatible, how is the situation with Objective-C++ and Objective-C?
From: https://en.wikipedia.org/wiki/Objective-C#Objective-C.2B.2B
Objective-C++ is a front-end to the GNU Compiler Collection, which can compile source files which use a combination of C++ and Objective-C syntax. Objective-C++ adds to C++ the extensions Objective-C adds to C. As nothing is done to unify the semantics behind the various language features, certain restrictions apply:
A C++ class cannot derive from an Objective-C class and vice versa.
C++ namespaces cannot be declared inside an Objective-C declaration.
Objective-C classes cannot have instance variables of C++ classes which do not have a default constructor or which have one or more virtual methods, but pointers to C++ objects can be used as instance variables without restriction (allocate them with new in the -init method).
C++ "by value" semantics cannot be applied to Objective-C objects, which are only accessible through pointers.
An Objective-C declaration cannot be within a C++ template declaration and vice versa. However, Objective-C types, (e.g., Classname *) can be used as C++ template parameters.
Objective-C and C++ exception handling is distinct; the handlers of each cannot handle exceptions of the other type.
Care must be taken since the destructor calling conventions of Objective-C and C++’s exception run-time models do not match (i.e., a C++ destructor will not be called when an Objective-C exception exits the C++ object’s scope). The new 64-bit runtime resolves this by introducing interoperability with C++ exceptions in this sense
Objective-C++ simply allows Objective-C and C++ code to be mixed (with caveats). It's not really a language on its own so much as a mechanism for allowing the two languages to intermix.
C and C++ are not directly compatible. Neither is a superset of the other (though most C is valid C++). Objective-C is a strict superset of C, and Objective-C++ is a strict superset of C++. Those are the only statements you can make (except trivially reversing it).
It's hard to answer this question confidently without understanding what definition of "different language" you want to apply.
Objective-C is a superset of C: it adds some additional syntax on top of the C language. Objective-C++ is a superset of C++ in the same way.
C and C++ are actually different languages. Although C++ is designed to be compatible, there is some C that is not valid C++, and vice versa.
So, I'd say, yes, Objective-C++ is a different language from Objective-C, because C++ is a different language from C. However, I wouldn't call them totally different.
At first glance, using the Objective-C++ dialect looks like a straightforward approach. It is the result of mashing C++ and Objective-C together in the same compiler, and robust implementations exist in GCC and now clang. Considering just how different the details of Objective-C and C++ are, the GCC hackers have done a great job of it. But as you start renaming your .m files to .mm to introduce chunks of C++, you quickly realise it's not quite so simple.
Header files and the C preprocessor in general have caused headaches for C, C++ and Objective-C programmers for decades. It gets worse when you try to mix the languages. Say you wanted to use the STL's map in an Objective-C class in your project. Apple's Foundation libraries to my knowledge don't contain a sorted, tree-based map; one of our StyleKit Components needs exactly that, for example. So we simply create an instance variable for the map in our class and away we go:
#include <map>
#interface MyClass : NSObject {
#private
std::map<int, id> lookupTable;
}
// ...
#end
However, std::map [2] only makes sense to a C++-aware compiler, and only after an #include [3], so this header now can only be #imported from Objective-C++ files. Any code using this class now needs to be converted to Objective-C++ itself, and importing from other headers leads to a cascade effect that quickly encompasses the whole project.
In some cases, this may be acceptable. However, switching a whole project or large parts of it across just to introduce a library which is used in one location is not only excessive; if you're the only one who knows C++ on a project with multiple Objective-C programmers, you might find this to be an unpopular idea. It might also cause issues in the same way that compiling pure C code with a C++ compiler rarely is completely hassle-free. Moreover, it means that code isn't automatically reusable in other Objective-C projects.
So it's always better not to mix up unless it's so important
To know more about strategies for using objective c++ in objective c and vice versa click here
Objective-C is probably the official term that you would put in a resume.
Objective-C++ is not really a new language, it just specifies a few things that allow Objective-C code to co-exist with C++ code. Saying your app was written in Objective-C and C++ or just Objective-C++ is probably what you want. Putting all of Objective-C, Objective-C++, C++ is redundant.
I would like to create a portable library for iPhone, that also could be used for other platforms.
My question is the fallowing:
Does anyone knows what is the best to be used on the iPhone: Objective-C or Objective-C++? Does it works with C++ the same way as Objective-C with C or not?
Reasons: Objective-C is a superset of C, but Objective-C++ is not a superset of C++.
Thanks in advance!
UPDATE: What about memory usage, speed in the same implementation of an use case?
UPDATE1: If anyone can provide any more information, he'll be welcome.
If you're writing a portable library, and don't need specific language features for it, why not write it in straight C? It can be easily called from C++, C, Objective-C, and many, many other languages.
If you require specific language features that aren't available in C, you should tell us what they are so you can get better advice =)
I believe your information is incorrect. Objective-C++ is a superset of C++. Any C++ is legal Objective-C++. In addition, you can mix Objective-C and C++ code in an Objective-C++ (usually .mm) file and (with some restrictions) mix Objective-C and C++ class instance variables within an Objective-C++ class. Objective-C++ is particularly useful for interfacing between Objective-C and a C++ library. Write your cross-platform library in C++. You can then call it from Objective-C++ within an application. Re-read the Objective-C++ section of the Objective-C language guide for more info.
The major downside to using Objective-C++ is increased compile times (Objective-C++ is even worse than C++ and the Clang LLVM compiler doesn't handle Objective-C++ yet). There is no performance difference between Objective-C and Objective-C++ beyond any differences in the code that's called (e.g. if you're a better C++ dev., your C++ will probably be more efficient than your C library and visa versa).
They're not really different languages. Objective-C++ is just Objective-C with slightly limited support for including C++ code. Objective-C is the standard dialect, but if you need to work with C++, there's no reason not to use it. AFAIK, the biggest practical difference (aside from allowing use of different libraries) is that Objective-C++ seems to compile a bit slower. Just be sure to read up on it first if you do decide to go that route, because the merging of C++ and Objective-C is not 100% seamless.
If you are going to use this library on platforms other than the iPhone and Mac OS, you should use C++. If you plan only to port it to Mac OS, then go ahead and use Objective-C. Objective-C++ is just a way to integrate existing C++ code into Objective-C projects. Thus, you would not write a library in it. You might, however, use Objective-C++ to use this library from an iPhone or Mac project.
The truth is you can use C or C++ in Xcode. The reason to use Objective C for Cocoa and Cocoa Touch (iphone) is because of it's ease of use and how it handles many of the memory issues you would come across on it's own. Objective C and Xcode work like a dream. I would also recommend checking out http://www.kevincallahan.org/software/accessorizer.html
Accessorizer is amazing and cuts development time into nothing.
Having said that I see no problem in writing functions/methods in C or C++ and using them within a part of your XCode project. Just do not expect to use Objective C to play as nicely on other platforms. Apple and Windows development IDE's are different and Microsoft has a nice habit for not making things as compatible with other environments (not just Apple.)
I am glad to hear someone out their trying to reuse their code for other projects : ) Too many people forget to create their own libraries these days and I haven't the slightest idea why.
I hope this helps. Cheers,
Matthew
Here is your caveat: Spend the hundred on becoming a developer and launch xcode the IDE you will be working with on the Mac - this would be the best way for you to decide as it is apparent that you do not fully understand how this platform works at all.
Please don't be rude to everyone trying to help you. This community is built on respect. The people here really actually do help out and care and there are few places like this on the net left.
Go for C or C++ - I do not see any reason for recommending one over the other without knowing more about your goals.
In terms of memory usage, C++ and C do demand more disciplined coding. In terms of speed, C and C++ will in virtually any case be faster than any ObjC/ObjC++ solution. I do frequently mix my Objective C applications with C and C++ code and was always pleased with the results. As Jonathan correctly stated, ObjectiveC++ is mostly a bridge for using C++ code/libraries within your Objective C application/s.
You can freely use C++ objects from within Objective C++. You can however NOT use Objective C/C++ objects within C++. So its a one-way-road. To overcome any limitations imposed by this restriction, simply wrap your C++ objects with Objective C++ classes where needed.
"Objective-C is a strict superset of C, and Objective-C++ is a strict superset of C++." - https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/CppRuntimeEnv/Articles/SymbolVisibility.html
I think I understand how Objective-C++ works in relation to Cocoa, and I am fairly versed in the basics of command-line C++ but sort of afraid to try mixing it with Objective-C. I can create a GUI with Interface Builder in Xcode, and even make classes (.h and .m files) for the interface automatically. The outlets, maybe actions (I still get those confused) leave the curly brackets open to put your own code in. So could I just put C++ code in those brackets to to take input from those buttons (and see the output, etc.)?
I guess if this is the case, one wouldn't have to learn any Obj-C, as long as they knew where to put the C++ code! Am I wrong?
Also, could anyone help me figure that out or at least point me somewhere I can learn more about this? This topic is fairly scarce on the web and I don't understand Apple's documentation.
My suggestion would be to have Objective-C files in your project (the .m file), then keep your Objective-C++ in separate files (as diciu mentions, .mm files).
One strategy would be use to these Objective-C++ classes simply as wrappers over C++ classes: write your code in C++, in .cpp files like normal. Then, when you need to access some functionality from your C++ from an Objective-C file, write a wrapper Objective-C++ class and call that from your Objective-C.
This last bit feels like a lot of work for small projects, and it is, but if you have a lot of C++ that you need to use, and a comparatively little bit of Objective-C to write, this works pretty well. (Imagine a situation where you are writing a Cocoa interface for a well-factored Windows or Linux program: where all the application logic was written in a platform agnostic manner, and you "just" have to write the UI in Cocoa to get it running on the Mac.
But, another reason for doing this wrapper approach is that Objective-C++ is a hybrid language, so has limitations as to what it's capable of, in both directions.
The thing you need to understand about objective-c++ is that the name is a lie. or at least implies a lot more than you might think.
Objective-c++ does not mean you can write hybrid objective-c++ "objects". It means that you can use c++, and objective c, in the same file. they can reference each other directly - the cannot inherit or derive from each other.
Rename .m files to .mm and you will be able to write (Objective-)C++ code in them.