When I am appending a NSString with another NSstring it Gives me an error "EXC BAD ACCESS"?

Solved....Check at bottom of Body..

I am using XCODE 4

I have an Money Calculator Application in which I have to press the digit buttons and I have to see it on the TextLabel.

Format like : "$ 500"

So for $ I am appending it..

The method works twice well but the third time it crashes..

Rest if you see the code you will have an Idea.

In my Application I have Three String variables...

-(void)viewDidLoad {

  current =[[NSString alloc] retain];

  current=[[NSUserDefaults standardUserDefaults] valueForKey:@"Total"]];



  NSString *newCurrent=[NSString stringWithFormat:@"$ %@",current];

  textViewer.text=newCurrent;

 NSLog(@"%@",current);

}

-(IBAction)buttonDigitPressed:(id)sender {

NSString *str= 开发者_运维问答(NSString* )[sender currentTitle];

//NSLog(@"1 The Value Of String %@",str);

NSLog(@"Befor Appending %@",current);


if([current isEqualToString:@"0"])
{
    current =  str;
}
else 
{

   current = [current stringByAppendingString:str];

    NSLog(@"After Appending %@",current);

}


NSString *newCurrent=@"$ ";

newCurrent = [newCurrent stringByAppendingString:current];

textViewer.text= newCurrent;  

} Error is 1st time it is working fine but

when I call it second time, current is Pointing to some Standard Time formatted value, some time it points to some file name value,

Error is: EXC BAD ACCESS

When I am doing it without newCurrent means without appending a letter it works fine.

-------SOLVED---------------- Every thing is Ok with My Code I just have to right [current retain]; where ever I am appending the String to the current.

As I was receiving the error EXC BAD ACCESS means I was referring to the Object which was released previously. So, I have retained the Object instead.

Try this code (without memory leaks):

-(void) viewDidLoad
{
    current=[[NSString alloc] initWithString:@"20"];
}

-(IBAction)buttonDigitPressed:(id)sender
{
    NSString *str= (NSString* )[sender currentTitle];

    NSString *nCurrent = [current stringByAppendingString:str];
    [current release];
    current = [nCurrent retain];

   NSString *newCurrent=[[NSString alloc] initWithFormat:@"a%@", current];
   textViewer.text= newCurrent;
   [newCurrent release];
}

- (void) dealloc
{
     [current release];
     [super dealloc];   
}

no need to alloc or retain the string in both the cases.

in viewdidload
s = [[NSString alloc] init];
s = @"a";

in button click

NSString *newStr = [NSString stringWithFormat:@"b"];
s = [s stringByAppendingString:newStr];
NSLog(@"s is :%@",s);

Hello Arpit,

You can declare property of nsstring in .h file and synthesize it in .m file so i think its help you.

.h file

@property (nonatomic,retain) 
NSString *current;

.m file

@synthesize current;

Theres a lot of issues here.

1. you have a memory leak in your viewDidLoad when you set current = to a newly allocated object then replace it with @"20"; you've now lost your pointer to the allocated memory. the correct way to do this would be simply to remove the alloc line.
2. you have another memory leak when you set newCurrent = [newCurrent stringByAppendingString:current]; for the same reason as 1.

You either need to manage your memory better or just use NSMutableStrings. Change current to be a NSMutableString alloc/init it in your init or viewDidLoad and then just use [current appendString:str];

based on your code you pasted I'd do the following.

in your @interface declare a property

@property (nonatomic, retain) NSString *current;

in your @implementation @synthesize it

@synthesize current; 

- (void) viewdidload
{
    self.current = @"20";
}

-(IBAction)buttonDigitPressed:(id)sender
{
    NSString *str= (NSString* )[sender currentTitle];
    self.current = [self.current stringByAppendingString:str];

    NSString *newCurrent = @"a";
    newCurrent = [newCurrent stringByAppendingString:self.current];

    textViewer.text = newCurrent;
}