iphone NSString Array

Question

Hi, I declared

NSString    *dayinfield[43];

and fill it in

-(void)DrawDemo {
dayinfield[2] = @"hallo";
dayinfield[3] = @"test";

// also i can read it
NSLog (@"show: %@",dayinfield[2]);
//works fine
}

but when i like to read its content in another function (same class)

-(void)ReadData
{
NSLog (@"show: %@",dayinfield[2]);
// I get random infos or “EXC_BAD_ACCESS
}

How do I initialize the NSString Array correct so I can reach its content in each of my functions??

Thanks chris

Answer 1

This would happen if you never initialized the array (or the parts of it you are accessing) - if you haven't called -DrawDemo before -ReadData or used different indices than the ones posted here, the array would simply contain garbage values.

Try to initialize the array contents to nil or @"" in your initializer method and see if the problem persists.

Alternatively consider using a suitable Cocoa container.

Answer 2

If you only assign literals to the array elements, this should not be a problem. But if you use other strings, you have to retain the instances manually when using a C array.

By the way: Objective-C methods start with a lowercase letter.

Answer 3

It's memory is probably being released before your second call. Assuming you have declared dayinfield as an ivar (and the fact that you don't get bad access all the time) your string aren't properly retained.

Initialise the strings like this:

dayinfield[2] = [[NSString alloc] initWithString:@"hallo"];
dayinfield[3] = [[NSString alloc] initWithString:@"test"];

and you should release them after you're class is being deallocated (See Memory Management Guide).

Also, obviously it depends on what you want to do, but it might be easier if you use NSArray instead of C arrays.

Answer 4

Please change your code to the following

In your .H file

NSArray* daysInField[50]; NSString* data;

In your viewDidLoad you can initialize all 50 members

-(void)DrawDemo {
data = @"halo";
dayinfield[2] = data;
dayinfield[3] = @"test";

// also i can read it 
NSLog (@"show: %@",dayinfield[2]);
//works fine
}


-(void)ReadData
{
 NSLog (@"show: %@",[dayinfield objectAtIndex:2]);
// this should work
}

Answer 5

What you have in the OP should work although it is an exercise in sheer masochism to use old school C arrays with objects.

I ran this code:

@interface TestClass : NSObject {
    NSString *a[1];
}
- (void) drawDemo;
- (void) readData;
@end 

@implementation TestClass

- (void) drawDemo{
    a[0]=@"A Zero";
    a[1]=@"A One";
}//------------------------------------- (void) drawDemo------------------------------------

- (void) readData{
    NSLog(@"a[0]=%@,a[1]=%@",a[0],a[1]);
}//------------------------------------- (void) readData------------------------------------

@end

TestClass *tc=[[TestClass alloc] init];
[tc drawDemo];
[tc readData];

... and got this output:

a[0]=A Zero,a[1]=A One

Your problem is elsewhere in your code. There is no compelling reason to use C arrays with objects. You gain nothing and you have to watch them like a hawk to prevent errors.