NSMutableArray: add and extract struct

Question

I'm trying to store some data in an NSMutableArray. This is my struct:

typedef struct{
    int time;
    char name[15];
}person;

This is the code to add a person:

person h1;
h1.time = 108000;
strcpy(h1.name, "Anonymous");
[highscore insertObject:[NSValue value:&h1 withObjCType:@encode(person)] atIndex:0];

So, I try to extract in this way:

NSValue * value = [highscore objectAtIndex:0];
person p;
[value getValue:&p];
NSLog(@"%d", p.time);

The problem is that the final log doesn't show me 108000!
What is wrong?

Is there any particular reason you're using a c struct rather than an actual object? Unless you do, go with objects. — Regexident
– Regexident, Commented Jul 6, 2012 at 16:07
I don't know another way to store two type of data(int and string) in the same index. I have corrected "persona", sorry. — charles
– charles, Commented Jul 6, 2012 at 16:12

rob mayoff · Accepted Answer · 2012-07-06 17:01:01Z

2

Your code looks correct (and works for me), so I deduce that you aren't initializing highscore. So when you send the insertObject:atIndex: message to it, nothing happens. When you then send the objectAtIndex: method to it, you get nil back. When you send getValue: to the nil NSValue *value, it does nothing, so your person p is left filled with random stack garbage, which is why your NSLog doesn't print 108000.

answered Jul 6, 2012 at 17:01

rob mayoff

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Comments

Regexident · Accepted Answer · 2012-09-04 12:44:55Z

1

As stated in my initial comment there rarely is a reason to do this kind of stuff with pure c structs. Instead go with real class objects:

If you're unfamiliar with the syntax below you may want to look at these quick tutorials on ObjC 2.0 as well as read Apple's documentation:

Person Class:

// "Person.h":
@interface Person : NSObject {}

@property (readwrite, strong, nonatomic) NSString *name;
@property (readwrite, assign, nonatomic) NSUInteger time; 

@end

// "Person.m":
@implementation Person

@synthesize name = _name; // creates -(NSString *)name and -(void)setName:(NSString *)name
@synthesize time = _time; // creates -(NSUInteger)time and -(void)setTime:(NSUInteger)time

@end

Class use:

#import "Person.h"

//Store in highscore:

Person *person = [[Person alloc] init];
person.time = 108000; // equivalent to: [person setTime:108000];
person.name = @"Anonymous"; // equivalent to: [person setName:@"Anonymous"];
[highscore insertObject:person atIndex:0];

//Retreive from highscore:

Person *person = [highscore objectAtIndex:0]; // or in modern ObjC: highscore[0];
NSLog(@"%@: %lu", person.name, person.time);
// Result: "Anonymous: 108000"

To simplify debugging you may also want Person to implement the description method:

- (NSString *)description {
    return [NSString stringWithFormat:@"<%@ %p name:\"%@\" time:%lu>", [self class], self, self.name, self.time];
}

which will allow you to just do this for logging:

NSLog(@"%@", person);
// Result: "<Person 0x123456789 name:"Anonymous" time:108000>

edited Sep 4, 2012 at 12:44

answered Jul 6, 2012 at 16:24

Regexident

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2 Comments

charles Over a year ago

Thank you all, I correct all things, but the real mistake I've made was I forgot to initialize the array!

Regexident Over a year ago

@user1431646: still, go with objects. There is no reason not to. Yet hundreds in favor of it. Way easier name string handling and memory allocation just to begin with.

trojanfoe · Accepted Answer · 2012-07-06 16:16:55Z

0

Reimplement Person as an Objective-C object and reap the benefits:

Person.h:

@interface Person : NSObject
{
    int _time;
    NSString *_name;
}

@property (assign, nonatomic) int time;
@property (retain, nonatomic) NSString *name;

@end

Person.m:

#import "Person.h"

@interface Person
@synthesize time = _time;
@synthesize name = _name;

- (id)init
{
    self = [super init];
    if (self != nil)
    {
        // Add init here
    }
    return self;
}

- (void)dealloc
{
    self.name = nil;
    [super dealloc];
}

@end

answered Jul 6, 2012 at 16:16

trojanfoe

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2 Comments

Hampus Nilsson Over a year ago

There is no need to declare the private members in the interface, @property and @synthesize is enough. Also, with ARC the dealloc (and the init) are both unnecessary. With 4.5 even @synthesize can be removed, leaving only the property declarations.

trojanfoe Over a year ago

@HampusNilsson This is the style I prefer to use and this implementation should work across pretty much any compiler and memory environment.

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