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1. Top results related to what is the difference between objective c and objective c + +?

   • What is the difference between ivars and properties in Objective-C

     Top Answer

     Answered Aug 25, 2017 · 57 votes

     Number 1 differs from the other two by forward declaring the MyOtherObject class to minimize the amount of code seen by the compiler and linker and also potentially avoid circular references. If you do it this way remember to put the #import into the .m file.

     By declaring an @property, (and matching @synthesize in the .m) file, you auto-generate accessor methods with the memory semantics handled how you specify. The rule of thumb for most objects is Retain, but NSStrings, for instance should use Copy. Whereas Singletons and Delegates should usually use Assign. Hand-writing accessors is tedious and error-prone so this saves a lot of typing and dumb bugs.

     Also, declaring a synthesized property lets you call an accessor method using dot notation like this:

     self.otherObj = someOtherNewObject; // set it MyOtherObject *thingee = self.otherObj; // get it -

     Instead of the normal, message-passing way:

     [self setOtherObject:someOtherNewObject]; // set itMyOtherObject *thingee = [self otherObj]; // get it -

     Behind the scenes you're really calling a method that looks like this:

     - (void) setOtherObj:(MyOtherObject *)anOtherObject {- if (otherObject == anOtherObject) { return; }- MyOtherObject *oldOtherObject = otherObject; // keep a reference to the old value for a second otherObject = [anOtherObject retain]; // put the new value in [oldOtherObject release]; // let go of the old object} // set it-

     …or this

     - (MyOtherObject *) otherObject { return otherObject;} // get it-

     Total pain in the butt, right. Now do that for every ivar in the class. If you don't do it exactly right, you get a memory leak. Best to just let the compiler do the work.

     I see that Number 1 doesn't have an ivar. Assuming that's not a typo, it's fine because the @property / @synthesize directives will declare an ivar for you as well, behind the scenes. I believe this is new for Mac OS X - Snow Leopard and iOS4.

     Number 3 does not have those accessors generated so you have to write them yourself. If you want your accessor methods to have side effects, you do your standard memory management dance, as shown above, then do whatever side work you need to, inside the accessor method. If you synthesize a property as well as write your own, then your version has priority.

     Did I cover everything?

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     1/5

   • What is the difference between #import and #include in Objective-C?

     Top Answer

     Answered Sep 27, 2014 · 360 votes

     The #import directive was added to Objective-C as an improved version of #include. Whether or not it's improved, however, is still a matter of debate. #import ensures that a file is only ever included once so that you never have a problem with recursive includes. However, most decent header files protect themselves against this anyway, so it's not really that much of a benefit.

     Basically, it's up to you to decide which you want to use. I tend to #import headers for Objective-C things (like class definitions and such) and #include standard C stuff that I need. For example, one of my source files might look like this:

     #import <Foundation/Foundation.h>-#include <asl.h>#include <mach/mach.h>-

     Other Answers

     Answered Sep 17, 2010 · 387 votes

     There seems to be a lot of confusion regarding the preprocessor.

     What the compiler does when it sees a #include that it replaces that line with the contents of the included files, no questions asked.

     So if you have a file a.h with this contents:

     typedef int my_number;-

     and a file b.c with this content:

     #include "a.h"#include "a.h"-

     the file b.c will be translated by the preprocessor before compilation to

     typedef int my_number;typedef int my_number;-

     which will result in a compiler error, since the type my_number is defined twice. Even though the definition is the same this is not allowed by the C language.

     Since a header often is used in more than one place include guards usually are used in C. This looks like this:

     #ifndef _a_h_included_ #define _a_h_included_- typedef int my_number;- #endif-

     The file b.c still would have the whole contents of the header in it twice after being preprocessed. But the second instance would be ignored since the macro _a_h_included_ would already have been defined.

     This works really well, but has two drawbacks. First of all the include guards have to be written, and the macro name has to be different in every header. And secondly the compiler has still to look for the header file and read it as often as it is included.

     Objective-C has the #import preprocessor instruction (it also can be used for C and C++ code with some compilers and options). This does almost the same as #include, but it also notes internally which file has already been included. The #import line is only replaced by the contents of the named file for the first time it is encountered. Every time after that it is just ignored.

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     Answered Jul 11, 2013 · 70 votes

     I agree with Jason.

     I got caught out doing this:

     #import <sys/time.h> // to use gettimeofday() function#import <time.h> // to use time() function-

     For GNU gcc, it kept complaining that time() function was not defined.

     So then I changed #import to #include and all went ok.

     Reason:

     You #import <sys/time.h>:     <sys/time.h> includes only a part of <time.h> by using #defines

     You #import <time.h>:     No go. Even though only part of <time.h> was already included, as     far as #import is concerned, that file is now already completely included.

     Bottom line:

     C/C++ headers traditionally includes parts of other include files. So for C/C++ headers, use #include. For objc/objc++ headers, use #import.

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     2/5

   • What is the difference between an instance variable/method and a class variable/method in Objective-C?

     Top Answer

     Answered Aug 07, 2010 · 2 votes

     An instance method or variable applies to that instance. A class method (classes in Objective-C don't have variables, though they can be simulated in various ways) applies to the whole class.

     Consider the quintessential Dog class, which derives from the Mammal class (and so on up the tree of life.) A particular dog has a name and a collar and an owner--those are its properties. A particular dog may -bark or -chaseBall or -buryBoneInBackyard--those are its methods.

     The Dog class, on the other hand, has different methods. The Dog class has a +globalPopulation and may instantiate itself with a +dogWithDNA: factory method. The Dog class will have an +isExtinct method indicating whether the species as a whole is extinct (it's not, of course.)

     In short: class methods affect the entire class, while instance methods affect a particular instance of a class.

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     3/5

   • What's the difference between Objective-C and Cocoa?

     Top Answer

     Answered Jan 12, 2009 · 66 votes

     Objective-C is the language... it defines all the things like the keywords for defining objects, the syntax for messaging object, things like that.

     Cocoa is a development framework (it's actually an umbrella framework which combines three other frameworks, Foundation, AppKit and CoreData).

     These frameworks (Cocoa) define all the objects that are nice to use and interact with the operating system, as well as a number of functions. For example, Cocoa defines things like NSString and NSObject. Cocoa can currently be used with other language bindings, such as python or ruby, and used to be used with Java as well. So, if you were using Cocoa with Java, you would still get an NSString object, but you would call and use it from within a Java application.

     Without linking to one of the Cocoa frameworks, Objective-C comes with only a very basic Object class as a pre-defined root class.

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   • Objective C - difference between init and constructor?

     Top Answer

     Answered Nov 11, 2013 · 23 votes

     In Objective-C, the way an object comes to life is split into two parts: allocation and initialization.

     You first allocate memory for your object, which gets filled with zeros (except for some Objective-C internal stuff about which you don't need to care):

     myUninitializedObjectPointer = [MyClass alloc];-

     The next stage is initialization. This is done through a method that starts with init by convention. You should stick to this convention for various reasons (especially when using ARC), but from a language point of view there's no need to.

     myObjectPointer = [myUnitializedObjectPointer init];-

     or in one line:

     myObjectPointer = [[MyClass alloc] init];-

     In other languages these init methods are called constructors, but in Objective-C it is not enforced that the "constructor" is called when the object is allocated. It's your duty to call the appropriate init method. In languages like C++, C# and Java the allocation and initialization are so tightly coupled that you cannot allocate an object without also initializing it.

     So in short: the init methods can be considered to be constructors, but only by naming convention and not language enforcement. To Objective-C, they're just normal methods.

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2. stackoverflow.com › questions › 78411842objective c - How to make a Cocoa window in pure C++ - Stack ...

   stackoverflow.com › questions › 78411842

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   1 day ago · The problem with Cocoa is that is mostly uses Swift and Objective-C, rendering it almost impossible to make Cocoa linked to c++. I've tried a bunch of code snippets and none of them worked for some unexplained reason. But my logic is Objective-C++. Apparently, you can combine Objective-C with C++ in Objective-C++ files.

3. www.dhiwise.com › post › mastering-swift-nimbleUnderstanding Swift Nimble: A Comprehensive Guide

   www.dhiwise.com › post › mastering-swift-nimble

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   1 day ago · Nimble iOS leverages the power of the Nimble Matcher Framework to help assert Objective-C expressions. It supports Objective-C objects and Swift objects bridged to Objective-C, making it an ideal choice for testing iOS apps built in Objective-C or Swift. Swift and Nimble: Creating Efficient Testing Frameworks

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