Question

I’d like to do a series of string substitutions to removed xml-escaped chars such as '&'.

1) Is there an existing UIKit function that can do this?

2) If not, what’s the best way to do it without leaking memory? Here’s the idea:

-(NSString*) unescape:(NSString*)string {     string = [string stringByReplacingOccurrencesOfString:@'&apos;' withString:@'''];     string = [string stringByReplacingOccurrencesOfString:@'&amp;' withString:@'&'];     string = [string stringByReplacingOccurrencesOfString:@'&quot;' withString:@'\''];     string = [string stringByReplacingOccurrencesOfString:@'&gt;' withString:@'>'];     string = [string stringByReplacingOccurrencesOfString:@'&lt;' withString:@'<'];     return string; } 

But doesn’t that leak memory with each assignment? Or does stringByReplacingOccurrencesOfString return autoreleased strings? How do we confirm that stringByReplacingOccurrencesOfString strings are autoreleased? Or should we wrap them with [... autorelease]?

Even if they are autoreleased, it’s preferable to avoid autorelease on the iPhone. (See here). So then we would do:

-(NSString*) unescape:(NSString*)string {     NSString* string2 = [string stringByReplacingOccurrencesOfString:@''' withString:@'''];     // don't release 'string' because we didn't allocate or retain it     NSString* string3 = [string2 stringByReplacingOccurrencesOfString:@''' withString:@'''];     [string2 release];     NSString* string4 = [string3 stringByReplacingOccurrencesOfString:@''' withString:@'''];     [string3 release];     //...and so on }      

But that’s pretty ugly code. What’s the best way to write this code to do multiple substitutions? How would you do it?

Answer 1

Any cocoa method which returns a new object via a method that does not start with init or contain the word copy will return an autoreleased object. So the above code should have noleaks.

Although it may be easier to use a NSMutableString here. Then you just modify the string in place rather than creating a pile of autoreleased string objects, which should make things cleaner.

Also, how about a dictionary of mappings that you iterate through, finding the key and replacing with the value of each item. Maybe even save this as a plist in your app for easy tweaking later.