Why is NSString stringWithString returning pointer to copied string?
nsstring, objective-c
Solution
1) Whenever you're creating a string using the `@""` syntax, the framework will automatically cache the string. `NSString` is a very special class, but the framework will take care of it. When you use `@"Some String"` in multiple places of your app, they will all point to the same address in memory. Only when you're using something like `-initWithData:encoding`, the string won't be cached.
2) The other answers suggested that you should use `-copy` instead, but `-copy` will only create a copy of the object if the object is mutable. (like NSMutableString) When you're sending `-copy` to an immutable object (like NSString), it'll be the same as sending it `-retain` which returns the object itself.
NSString *originalString = @"Some String";
NSString *copy = [originalString copy];
NSString *mutableCopy1 = [originalString mutableCopy];
NSString *mutableCopy2 = [mutableCopy copy];
NSString *anotherString = [[NSString alloc] initWithString:originalString];
--> `originalString`, `copy`, `mutableCopy2` and `anotherString` will all point to the same memory address, only `mutableCopy1` points do a different region of memory.
Problem
I'm trying to copy an `NSString` value out of an `NSMutableArray` into a new variable. `NSString stringWithString` is returning an `NSString` with the same memory address as the object in my array. Why? ``` #import <Foundation/Foundation.h> int main(int argc, const char * argv[]) { @autoreleasepool { NSMutableArray *arr = [NSMutableArray arrayWithObject:@"first"]; NSLog(@"string is '%@' %p", [arr objectAtIndex:0], [arr objectAtIndex:0]); // copy the string NSString *copy = [NSString stringWithString:[arr objectAtIndex:0]]; NSLog(@"string is '%@' %p", copy, copy); } return 0; } ```