Question

Please check the below code, where I am creating multiple reference for an array

NSMutableArray *array1 = [[NSMutableArray alloc] init];
NSMutableArray *array2 = array1;
[array1 addObject:@"One"];
[array1 addObject:@"Two"];

NSLog (@"Array1 %@",array1);
NSLog (@"Array2 %@",array2);

Console output is

Array1 (
One,
Two ) Array2 (
One,
Two )

Both Array1 and Array2 reference to same address

Like wise I tried for NSMutableString, I didn’t work out

NSMutableString *str1 = [[NSMutableString alloc] init];
NSMutableString *str2 = str1;
str1 = @"Hello";

NSLog (@"Str1 : %@", str1);
NSLog (@"Str2 : %@", str2);

Console Output is Str1 Hello Str2 (null)

Is there any way to have reference to string ?

Answer 1

Everything is quite normal. With :

str1 = @"Hello";

str1 doesn’t point to the memory you allocated two lines above anymore. str2 didn’t change and still point to that memory place.

The example you gave doesn’t looks the same for arrays and string. In the first you add objects to one array, but don’t change the value of any pointer.

In the second you are modifiying the reference to an object.

The second example, should be written as something like :

NSMutableString *str1 = [[NSMutableString alloc] init];
NSMutableString *str2 = str1;
[str1 appendString:@"foo"];

NSLog (@"Str1 : %@", str1);
NSLog (@"Str2 : %@", str2);

Output :

Str1 : foo
Str2 : foo

Given two references on the same mutable string (one memory place), and using NSMutableString‘s method, both references will be modified.