If you got this message try __unsafe_unretained. It is only safe, if the objects in the struct are unretained. 
Example: If you use OpenFeint with ARC the Class OFBragDelegateStrings says this error in a struct.

    typedef struct OFBragDelegateStrings
    {
         NSString* prepopulatedText;
         NSString* originalMessage;
    } OFBragDelegateStrings;

 
to

    typedef struct OFBragDelegateStrings
    {
         __unsafe_unretained NSString* prepopulatedText;
         __unsafe_unretained NSString* originalMessage;
    } OFBragDelegateStrings;

**Rather** than using a **struct**, you can create an **Objective-C class** to manage the data instead.

That is because arc can&#39;t track objects in structs or unions (since they are at that point plain C pointers). 

Even though you marked the file/class in question with  `-fno-objc-arc` you might still pass an object controlled by arc to it as parameter, which would most likely result in a memory leak.

Looks like this now works without errors, probably after [this change][1].

i.e., You can put normal (strong) pointers to Objective-C objects in a C struct. It is managed by ARC e.g., it is unretained when the struct is destructed. Verified with:

```$ clang --version
Apple LLVM version 10.0.0 (clang-1000.11.45.2)
```

  [1]: https://reviews.llvm.org/D41228

Jshint.com is giving the error:

&gt; Line 36: var signin_found; Missing &quot;use strict&quot; statement.

Jshint.com requires &quot;use strict&quot;. What does this mean?

    &lt;input id=&quot;txtComputer&quot;&gt;

How do I make my text inside the input tag bigger? I want to make it 24 size font. It would also be good if I can change the font from the default

How to change the font and font size of an HTML input tag?

ARC forbids Objective-C objects in structs or unions despite marking the file -fno-objc-arc?
Why is this so?

I had the assumption that if you mark it -fno-objc-arc you don&#39;t have this restriction.

ARC forbids Objective-C objects in structs or unions despite marking the file -fno-objc-arc

<p>ARC forbids Objective-C objects in structs or unions despite marking the file -fno-objc-arc?
Why is this so?</p>
<p>I had the assumption that if you mark it -fno-objc-arc you don't have this restriction.</p>


I am looking for some best barcode libraries on all platforms. I know zxing but wondering more libraries besides it. Any help is appreciated~

looking for best barcode scanner library, besides zxing

How To Add Month To NSDate Object?

    NSDate *someDate = [NSDate Date] + 30Days.....;

How to add one month to an NSDate?

I&#39;m using storyboards and I have a UITableView.  I have a segue setup that pushes from my table to the detail VC.  But which method should I use to handle this?  I&#39;ll have to pass a couple objects to the detail view.  But do I use `didSelectRowAtIndex` or `-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender`?

Use didSelectRowAtIndexPath or prepareForSegue method for UITableView?

I am sending push notifications from php job application to iphone. I am sending push notifications regarding new jobs. Is this possible that when user click on the view of push notification pop up , then user redirect to the particular job in the device.

I mean I wanted to know can I send any custom data with push notification like jobId,something else....so that Iphone end Can retrieve and show the particular job ?

Thanks.

Apple Push Notification with Sending Custom Data

Within the iOS Simulator, is it possible to access the App Store?  

That is, can I install the App Store application within the Simulator and download applications through it to the iOS Simulator?  If so, how?

Can I access the App Store from within the iOS Simulator?

Is there a more intelligent way to rewrite this?

    if ([cardName isEqualToString:@&quot;Six&quot;]) {
        [self setValue:6];
    } else if ([cardName isEqualToString:@&quot;Seven&quot;]) {
        [self setValue:7];
    } else if ([cardName isEqualToString:@&quot;Eight&quot;]) {
        [self setValue:8];
    } else if ([cardName isEqualToString:@&quot;Nine&quot;]) {
        [self setValue:9];
    } 

Can Objective-C switch on NSString?

I use custom button in my app named &quot;addButton&quot; and I want to border it with white color how can i get the white color border around my custom button?

How to create border in UIButton?

I have a MKAnnotation with an custom pin image. However the pin(MKAnnotationView) centers the image in relation to the specified coordinate. I want to set the point of the coordinate at the bottom center of the image, not center.

I&#39;ve tried using `annView.centerOffset = CGPointMake(-12, -28);`. But the problem is that `centerOffset` isn&#39;t relevant to the maps zoom level. 

One can do this both in the JS API and in Android. Is there any possibility to do this in objective-c?

..fredrik



MKAnnotation image offset with custom pin image

C11 adds, among other things, &#39;Anonymous Structs and Unions&#39;.

I poked around but could not find a clear explanation of when anonymous structs and unions would be useful. I ask because I don&#39;t completely understand what they are. I get that they are structs or unions without the name afterwards, but I have always (had to?) treat that as an error so I can only conceive a use for named structs.

When are anonymous structs and unions useful in C11?

I want to copy an identical struct into another and later on use it as a comparance to the first one. The thing is that my compiler gives me a warning when Im doing like this! Should I do it in another way or am I doing this wrong:

In header File:

    extern struct RTCclk
    {
	uint8_t second;
	uint8_t minute;
	uint8_t hour;
	uint8_t mday;
	uint8_t month;
	uint8_t year;
    }
    RTCclk;

In C file:

    struct RTCclk RTCclk;
    struct RTCclk RTCclkBuffert;
    
    void FunctionDO(void)
    {
       ... // Some Code
       /* Copy first struct values into the second one */
       memcpy(&amp;RTCclk, &amp;RTCclkBuffert, sizeof RTCclk);
    }


Copy struct to struct in C

In C#, Structs are managed in terms of values, and objects are in reference. From my understanding, when creating an instance of a class, the keyword `new` causes C# to use the class information to make the instance, as in below:

    class MyClass
    {
        ...
    }
    MyClass mc = new MyClass();

For struct, you&#39;re not creating an object but simply set a variable to a value:

    struct MyStruct
    {
        public string name;
    }
    MyStruct ms;
    //MyStruct ms = new MyStruct();     
    ms.name = &quot;donkey&quot;;

What I do not understand is if declare variables by `MyStruct ms = new MyStruct()`, what is the keyword `new` here is doing to the statement? . If struct cannot be an object, what is the `new` here instantiating?

What does the keyword &quot;new&quot; do to a struct in C#?

I can do this on initialization for a struct Foo:

    Foo foo =  {bunch, of, things, initialized};

but, I can&#39;t do this:

    Foo foo;
    foo = {bunch, of, things, initialized};

So, two questions:

1. Why can&#39;t I do the latter, is the former a special constructor for initialization only? 
2. How can I do something similar to the second example, i.e. declare a bunch of variables for a struct in a single line of code after it&#39;s already been initialized? I&#39;m trying to avoid having to do this for large structs with many variables:
    
        Foo foo;

        foo.a = 1;
        foo.b = 2;
        foo.c = 3;
        //... ad infinitum


how to assign multiple values into a struct at once?

&gt; **Possible Duplicate:**  
&gt; [Why doesn&amp;#39;t GCC optimize structs?](https://stackoverflow.com/questions/118068/why-doesnt-gcc-optimize-structs)  
&gt; [Why doesn&amp;#39;t C++ make the structure tighter?](https://stackoverflow.com/questions/6730664/why-doesnt-c-make-the-structure-tighter)  

&lt;!-- End of automatically inserted text --&gt;

Consider the following example on a 32 bit x86 machine:

Due to alignment constraints, the following struct

    struct s1 {
        char a;
        int b;
        char c;
        char d;
        char e;
    }

could be represented more memory-efficiently (12 vs. 8 bytes) if the members were reordered as in

    struct s2 {
        int b;
        char a;
        char c;
        char d;
        char e;
    }

I know that C/C++ compilers are not allowed to do this. My question is why the language was designed this way. After all, we may end up wasting vast amounts of memory, and references such as `struct_ref-&gt;b` would not care about the difference.



**EDIT**: Thank you all for your extremely useful answers. You explain very well why rearranging doesn&#39;t work because of the way the language was designed. However, it makes me think: Would these arguments would still hold if rearrangement was part of the language? Let&#39;s say that there was some specified rearrangement rule, from which we required at least that

 1. we should only reorganize the struct if actually necessary (don&#39;t do anything if the struct is already &quot;tight&quot;)
 2. the rule only looks at the definition of the struct, not inside inner structs. This ensures that a struct type has the same layout whether or not it is internal in another structure
 3. the compiled memory layout of a given struct is predictable given its definition (that is, the rule is fixed)

Adressing your arguments one by one I reason:

*  _Low-level data mapping, &quot;element of least surprise&quot;_: Just write your structs in a tight style yourself (like in @Perry&#39;s answer) and nothing has changed (requirement 1). If, for some weird reason, you want internal padding to be there, you could insert it manually using dummy variables, and/or there could be keywords/directives.

*  _Compiler differences_: Requirement 3 eliminates this concern. Actually, from @David Heffernan&#39;s comments, it seems that we have this problem today because different compilers pad differently?

*  _Optimization_: The whole point of reordering is (memory) optimization. I see lots of potential here. We may not be able to remove padding all together, but I don&#39;t see how reordering could limit optimization in any way.

*  _Type casting_: It seems to me that this is the biggest problem. Still, there should be ways around this. Since the rules are fixed in the language, the compiler is able to figure out how the members were reordered, and react accordingly. As mentioned above, it will always be possible to prevent reordering in the cases where you want complete control. Also, requirement 2 ensures that type-safe code will never break.

The reason I think such a rule could make sense is because I find it more natural to group struct members by their contents than by their types. Also it is easier for the compiler to choose the best ordering than it is for me when I have a lot of inner structs. The optimal layout may even be one that I cannot express in a type-safe way. On the other hand, it would appear to make the language more complicated, which is of course a drawback.

Note that I am not talking about changing the language - only if it could(/should) have been designed differently.

I know my question is hypothetical, but I think the discussion provides deeper insight in the lower levels of the machine and language design.

I&#39;m quite new here, so I don&#39;t know if I should spawn a new question for this. Please tell me if this is the case.

Why can&#39;t C compilers rearrange struct members to eliminate alignment padding?

I have made an application for my client by keeping target iOS as 4.  
But since the application still not submitted to Apple store, my client is planning to upgrade it for iOS 5.0.  

For this I read the [guideline from Apple][1] and found that &quot;Only user-generated data or that cannot otherwise be recreated by your application, should be stored in the &lt;Application_Home&gt;/Documents directory and rest should be stored to &lt;Application_Home&gt;/Library/Caches directory&quot; 

In my application, I am using server model of in-app purchase for non-consumable product. For this I am storing all my downloaded data (which are basically books or magazines) to Documents directory. The Database is also present in the same directory which contains the details about the downloaded products.  

My question is,  
1. Should I have to change my code to store the downloaded data to Library/Caches directory instead of to the Documents directory?  
2. Where should my database file be placed (to Documents or Caches)?  

If I put it products in the Caches then I have to change the logic of retrieval also, since it is considered that if record is present in database, there is no need change the existence of the file and it directly opens it when user clicks on the magazine.  

Kindly guide me on this issue.  
Thanks in advance.

**UPDATED:**  
I am updating this for those who are still not sure about this problem.  
Using the guideline of accepted answer, I have implemented this in 2 of my applications and submitted them to Apple Store. Both were approved in review.  
This may promote that the solution suggested in the accepted answer is correct.  

  [1]: https://developer.apple.com/icloud/documentation/data-storage/

iOS 5 does not allow to store downloaded data in Documents directory?

In iOS 5 I have a Storyboard with a modal view controller, that I would like to display if its the user&#39;s first time in the app, after that I would like to skip this view controller.

I set an NSDefault key to handle this but when I check to see if this is set and then use performSegueWithIdentifier to initiate the segue, nothing happens.  If i put this segue behind a button it works fine...

Perform Segue on ViewDidLoad

On the tech talk 2011 I saw a speech about the new `UIAppearance` [protocol][1].  There is not a lot of documentation out there yet. I will shortly summarize what I remember to explain where my question is coming from:

---
**About `UIAppearance`:**

So far you had to customize EVERY navigation bar (toolbar, etc.) property in all your app view controllers. With the new appearance property you can do it in only one place for all navigation bars in your app. For instance: if you want to customize your Navigation bar background image you could do it like this:

    [[UINavigationBar appearance] setBackgroundImage:
       [UIImage imageNamed:@&quot;MyImageName&quot;] forBarMetrics:UIBarMetricsDefault]; 

This will set the background image of ALL navigation bars within your application. With the `barMetrics` you specify whether you want the image to be used also in landscape mode or not.

If you want to specify the appearance to be applied only in some view controllers there is also a method in the docs to control that by specifying where your objects are located:

    [[UIBarButtonItem appearanceWhenContainedIn:
        [ABPeoplePickerNavigationController class], nil] setTintColor:myNavBarColor];

Also worth to mention is, if you have single customized instances, differing from your appearance settings, theses instances will not be effected by the appearance proxy.  

-----------------------------------------------------------------------------------------
**Some questions:**

**a) How do I know which properties of a class work with the appearance property?** For e.g. since `UITableView` conforms to the UIAppearance protocol I was thinking I could do something like

    [[UITableView appearance] setBackgroundColor:mytableViewColor];

to manipulate the background color of all my table views, but I can&#39;t!  

**b) Is there a list of all classes that are manipulatable with the appearance property?** 

**c) At what point is the appearance customization being called?** I was hoping to make changes threw the appearance property at runtime, but unfortunately the changes aren&#39;t taking place.  


  [1]: https://developer.apple.com/documentation/uikit/uiappearance

iOS 5: Curious about UIAppearance

My objective is to create a tabbed application, then the view for each of the tabs are constructed in separate storyboards.

![Storyboard screenshot][1]

My mainstoryboard is a tab view.

Then I create a secondary storyboard (storyboard#2) with 2 View Controllers. The first view controller (also ticked as initial) have a button, and segue (modal) to 2nd view. ![First view controller][2]

I managed to load the view by subclassing and overriding loadView from storyboard#2.
![loadView override][3]

Here&#39;s the simulator output.

![Simulator][4]

When click on the &quot;click me&quot; button, I get a `EXC_BAD_ACCESS`. The segue does not work, seems like the second storyboard is not being loaded completely.

Has anyone tried to do this before and get it working? There&#39;s a youtube video from SkillMaster.net but he does not demonstrate if a segue is working under the secondary storyboard. the video is here: http://youtu.be/D4_twoYvB4M

Thanks for any input and help!

Screenshots:

* http://www.box.com/s/njnyzjoqg8pnqofv838m
* http://www.box.com/s/8dqygclmp5ic86e47bi5
* http://www.box.com/s/k7foe7gpgh2rs3y8gqxd
* http://www.box.com/s/rym111x7xqxqao51ruip

  [1]: http://i.stack.imgur.com/Nw6Zn.png
  [2]: http://i.stack.imgur.com/s848R.png
  [3]: http://i.stack.imgur.com/z7Mgw.png
  [4]: http://i.stack.imgur.com/MvnU6.png

Using Multiple Storyboards in iOS

Is it really so simple now in iOS5?

I used to perform a background fetch using this code in my AppDelegate:

    dispatch_queue_t downloadQueue = dispatch_queue_create(&quot;DownloadQueue&quot;, NULL);
    dispatch_async(downloadQueue, ^{
            self.myDownloadClass = [[MyDownloadClass alloc]initInManagedObjectContext:self.managedObjectContext];
            [self.myDownloadClass download];
        });
        
    dispatch_release(downloadQueue);

My download class performs an NSURLConnection to fetch some XML data, uses NSXMLParser to parse the data, and then updates a complex schema in core data. I would always switch to the main thread to actually update the core data. Messy code, with lots of calls to dispatch_sync(dispatch_get_main_queue()....

My new code looks like this:

    NSManagedObjectContext *child = [[NSManagedObjectContext alloc]initWithConcurrencyType:NSPrivateQueueConcurrencyType];
    [child setParentContext:self.managedObjectContext];
    
    [child performBlock:^{
    	self.myDownloadClass = [[MyDownloadClass alloc]initInManagedObjectContext:child];
    	[self.myDownloadClass download];
    	}];

along with a small change to some other code in my AppDelegate to set the parent model object context type to NSMainQueueConcurrencyType:

    - (NSManagedObjectContext *)managedObjectContext
    {
        if (__managedObjectContext != nil)
        {
            return __managedObjectContext;
        }
        
        NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
        if (coordinator != nil)
        {
            __managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
            [__managedObjectContext setPersistentStoreCoordinator:coordinator];
        }
        return __managedObjectContext;
    }

It seems to work very well. The entire update process still runs in a separate thread, but I did not have to create a thread. Seems like magic.

Just remember if you want to commit your changes to the physical core data files, you have call save: on the parent context as well.

I didn&#39;t really ask a question here. I&#39;m posting this so it helps others because everything I found when searching for the new iOS5 managed object context methods only gave high level details with no code examples And all the other searches for fetching core data in the background are old, sometimes very old, and discuss how to do it pre-iOS5.

Core Data background fetching via new NSPrivateQueueConcurrencyType

Just want to make sure that I got it right:

 1. Do I need to `__unsafe_unretain` objects that I don&#39;t own?
 2. If an object is `__unsafe_unretained` Do I need to use `assign` in the `@property`? Does that mean that the object is not retained, and just refers to the object I assign to?
 3. When would I want to use it except of delegates?
 4. Is that an ARC thing or was it in use before?

ARC - The meaning of __unsafe_unretained?

I&#39;m reading apple&#39;s documentation about &quot;Memory Management for Dispatch Queues&quot;:

&gt; Even if you implement a garbage-collected application, you must still retain and release your dispatch queues and other dispatch objects. Grand Central Dispatch does not support the garbage collection model for reclaiming memory.

I know that ARC is not a garbage collector but I&#39;d like to be sure that I don&#39;t need to dispatch_retain and dispatch_release my dispatch_queue_t

Does ARC support dispatch queues?

I need to generate a UUID string in some code with ARC enabled.

After doing some research, this is what I came up with:

    CFUUIDRef uuid = CFUUIDCreate(NULL);
    NSString *uuidStr = (__bridge_transfer NSString *)CFUUIDCreateString(NULL, uuid);
    CFRelease(uuid);

Am I correctly using `__bridge_transfer` to avoid leaking any objects under ARC?

Generate a UUID string with ARC enabled

I&#39;ve yet to use ARC, since the majority of the code in the project I&#39;m working on at the moment was written pre-iOS 5.0. 

I was just wondering, does the convenience of not retaining/releasing manually (and presumably more reliable code that comes as a result?) outweigh any &#39;cost&#39; of using ARC?
What are your experiences of ARC, and would you recommend it?

So:

 - How much benefit can ARC bring to a project?
 - Does ARC have a cost like garbage collection in Java?
 - Have you been using ARC and if so, how have you found it so far?


To ARC or not to ARC? What are the pros and cons?

I&#39;m trying to complete the puzzle.

`__strong` is the default for all Objective-C retainable object pointers like NSObject, NSString, etc.. It&#39;s a strong reference. ARC balances it with a `-release` at the end of the scope.

`__unsafe_unretained` equals the old way. It&#39;s used for a weak pointer without retaining the retainable object.

`__weak` is like `__unsafe_unretained` except that it&#39;s an auto-zeroing weak reference meaning that the pointer will be set to nil as soon as the referenced object is deallocated. This eliminates the danger of dangling pointers and EXC_BAD_ACCESS errors.

But what exactly is `__autoreleasing` good for? I&#39;m having a hard time finding practical examples on when I need to use this qualifier. I believe it&#39;s only for functions and methods which expect a pointer-pointer such as:

    - (BOOL)save:(NSError**);

or

    NSError *error = nil;
    [database save:&amp;error];

which under ARC has to be declared this way:

    - (BOOL)save:(NSError* __autoreleasing *);

But this is too vague and I&#39;d like to fully understand *why*. The code snippets I find place the __autoreleasing inbetween the two stars, which looks weird to me. The type is `NSError**` (a pointer-pointer to NSError), so why place `__autoreleasing` inbetween the stars and not simply in front of `NSError**`? 

Also, there might be other situations in which I must rely on `__autoreleasing`.

Content Type	Original Author	Original Content on Stackoverflow
Question	Zsolt	View Question on Stackoverflow
Solution 1 - Iphone	zeiteisen	View Answer on Stackoverflow
Solution 2 - Iphone	János	View Answer on Stackoverflow
Solution 3 - Iphone	voidStern	View Answer on Stackoverflow
Solution 4 - Iphone	Hiroshi Ichikawa	View Answer on Stackoverflow

ARC forbids Objective-C objects in structs or unions despite marking the file -fno-objc-arc

Iphone Problem Overview

Iphone Solutions

Solution 1 - Iphone

Solution 2 - Iphone

Solution 3 - Iphone

Solution 4 - Iphone

How to change the font and font size of an HTML input tag?

Jshint.com requires "use strict". What does this mean?

Attributions