How to better initialize strings to avoid dead stores

Question

I found a few questions like this but I couldn't find this particular question. I have a number of strings that are initialized as

NSString *string = [[NSString alloc] init];

which are then assigned a value depending on the results of an if/else block:

if ([anotherThing isEqualToString:@"boogers"]) {
    string = [NSString stringWithFormat:@"some characters"];
} else {
    string = [NSString stringWithFormat:@"some _other_ characters"];
}

and then string is used later in the method.

How can I accomplish this without leaving a dead store at the alloc/init stage? If I alloc inside the if (or the else), the string is gone by the time I need it several lines down.

Why are you allocing and initing the "dead" string in the first place? Why not set it to `nil` since your execution path guarantees it will be assigned? — vcsjones, Nov 29 '12 at 22:09
In addition to Joe Hankin's answer, if your strings don't need to be formatted, you can just use `string = @"some characters";`. — msoler, Nov 29 '12 at 22:21
Thanks, @vcsjones. I didn't know you could do that. @msoler, is there a good explanation somewhere on the real difference between `stringWithFormat:` and `stringWithString:`? I'm unsure how a formatted string differs from any others. — ele, Nov 29 '12 at 22:36
`stringWithFormat:` is for creating a string that includes the contents of variables, e.g. `[NSString stringWithFormat:@"There are %d states in %@", anInt, anotherString];` `stringWithString:` is just a copy constructor. — Joe Hankin, Nov 29 '12 at 22:42
Check Apple's official doc about [formatting string objects](https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/Strings/Articles/FormatStrings.html#//apple_ref/doc/uid/20000943) and [string format specifiers](https://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265). — msoler, Nov 29 '12 at 22:50

Joe Hankin · Accepted Answer · 2012-11-29T23:15:01.480

5

You don't have to initialize the string on that first line -- you just need to declare it:

NSString *string = nil;
if ([anotherThing isEqualToString:@"boogers"]) {
    string = @"some characters";
} else {
    string = @"some _other_ characters";
}

edited Nov 29 '12 at 23:15

answered Nov 29 '12 at 22:09

Joe Hankin

950
8
15

Why are you using stringWithFormat: in your answer when you correctly stated in your comments, that it should be used when you have a format string? – rdelmar Nov 29 '12 at 22:56
Fair point -- I was copying Erik's original code, but I've edited my post to reflect your comment. – Joe Hankin Nov 29 '12 at 23:15

score 0 · Answer 2 · answered Nov 29 '12 at 22:21

The [NSString stringWithFormat:] will initialize a new NSString object for you, basically what you are doing is declaring a new object each time, just set the pointers for your strings as NSSTring *someString, *someOtherString, *allTheStringsYouNeed; and then use any class method to initialize it even @"Characters"; will work correctly as the compiler do it at runtime for you.

How to better initialize strings to avoid dead stores

2 Answers2