objective-c - iOS中的c结构实现

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

问题

1. appFlags = (AppFlags *)newAppFlags();

给出函数 newAppFlags 的隐式声明在 C99 中无效

1. appFlags->sharedCompletedStepMask = 0; appFlags.sharedCompletedStepMask = 0;

'struct _appFlags' 类型的不完整定义成员引用类型'AppFlags *'（又名'struct _appFlags *'）是一个指针；也许你打算使用'->'？

给出以下警告和错误。这是我第一次在这里发布问题，所以请对 html 或编辑提出建议。谢谢！

Answer 1

当你这样写

struct {
    unsigned int sharedCompletedStepMask:3;
} _appFlags;

您正在声明一个未命名结构的变量 _appFlags。

你可能是说

struct _appFlags {
    unsigned int sharedCompletedStepMask:3;
};

或者你可以写

typedef struct _appFlags {
    unsigned int sharedCompletedStepMask:3;
} AppFlags;