c struct implementation in iOS - objective-c

Question

SSharedAppState.h
#import <Foundation/Foundation.h>
enum {
SharedCompletedStepNone = 0,
SharedCompletedStepOne = 1 << 0,
SharedCompletedStepTwo = 2 << 1,
SharedCompletedStepThree = 3 << 2
};
typedef NSUInteger SharedCompletedSteps;
#interface SSharedAppState : NSObject
{
struct {
unsigned int sharedCompletedStepMask:3;
} _appFlags;
}
#property (assign, nonatomic) SharedCompletedSteps sharedCompletedStep;
+(id)sharedInstance;
#end
SSharedAppState.m
#import "SSharedAppState.h"
#pragma mark - C functions
#pragma mark - Interface Extension
typedef struct _appFlags AppFlags;
#interface SSharedAppState ()
#property (unsafe_unretained, nonatomic) AppFlags *appFlags;
-(void *)newAppFlags;
#end
#pragma mark - Implementation
#implementation SSharedAppState
#synthesize appFlags;
#pragma mark - Iniitalizer
-(id)init
{
self = [super init];
if (self) {
// appFlags = (AppFlags *)malloc(sizeof(_appFlags));
appFlags = (AppFlags *)newAppFlags();
appFlags->sharedCompletedStepMask = 0;
appFlags.sharedCompletedStepMask = 0;
}
return self;
}
+(SSharedAppState *)sharedInstance
{
static dispatch_once_t onceToken;
static id sharedInstance;
dispatch_once(&onceToken, ^{
sharedInstance = [[self alloc] init];
});
return sharedInstance;
}
#pragma makr - Struct _appFlags
-(void *)newAppFlags
{
AppFlags *instance = (AppFlags *)malloc(sizeof(_appFlags));
return instance;
}
#end
Questions
appFlags = (AppFlags *)newAppFlags();
gives implicit declaration of function newAppFlags is invalid in C99
appFlags->sharedCompletedStepMask = 0;
appFlags.sharedCompletedStepMask = 0;
Incomplete definition of type 'struct _appFlags'
Member reference type 'AppFlags *' (aka 'struct _appFlags *') is a pointer; maybe you meant to use '->'?
Gives following warnings and error.
These is my first time to post questions here so please advice on html or editing. Thankyou!

Answer 1

When you write like this
struct {
unsigned int sharedCompletedStepMask:3;
} _appFlags;
you are declaring a variable _appFlags of an unnamed struct.
you probably meant
struct _appFlags {
unsigned int sharedCompletedStepMask:3;
};
or you could write
typedef struct _appFlags {
unsigned int sharedCompletedStepMask:3;
} AppFlags;