iOS 5 Programming Cookbook

1.8. Allocating and Making Use of Strings

Problem

You want work with strings in Objective-C

Solution

Use NSString and NSMutableString classes.

Discussion

The NSString and NSMutableString classes allow you to store a string of characters in memory. The NSString class is immutable, meaning that once it is created, its contents cannot be modified. Mutable strings represented with the NSMutableString can be modified once they are created. We will see an example of both of these classes very soon.

Objective-C strings should be placed inside double quotes. The starting double-quote should be prefixed with an at sign (@). For instance, the sentence Hello, World, represented as a string in Objective-C, is written like so:

@"Hello, World"

There are various ways of placing a string inside an instance of NSString or NSMutableString classes. Here is how:

NSString *simpleString = @"This is a simple string";

NSString *anotherString =
  [NSString stringWithString:@"This is another simple string"];

NSString *oneMorestring =
  [[NSString alloc] initWithString:@"One more!"];

NSMutableString *mutableOne =
  [NSMutableString stringWithString:@"Mutable String"];

NSMutableString *anotherMutableOne =
  [[NSMutableString alloc] initWithString:@"A retained one"];

NSMutableString *thirdMutableOne =
  [NSMutableString stringWithString:simpleString];

If you are working with strings, you are probably going to need the length of your string objects from time to time to make specific decisions at runtime. Imagine this scenario: ...