string tokenizer in ios

Question

I like to tokenize a string to characters and store the tokens in a string array. I am trying to use following code which is not working as I am using C notation to access the array. What needs to be changed in place of travel path[i]?

NSArray *tokanizedTravelPath= [[NSArray alloc]init];
for (int i=0; [travelPath length]; i++) {
    tokanizedTravelPath[i]= [travelPath characterAtIndex:i];

Splitting a string into individual characters is not "tokenizing" it. — Lily Ballard, Sep 18 '12 at 01:50

Ramy Al Zuhouri · Answer 1 · 2012-09-18T11:21:44.283

1

You need a NSMutableArray to set every element of the array (otherwise you can't change its objects).Also, you can only insert objects in the array, so you can:
- Insert a NSString containing the character;
- Use a C-style array instead.
This is how to do with the NSMutableArray:

NSMutableArray *tokanizedTravelPath= [[NSMutableArray alloc]init];
for (int i=0; i<[travelPath length]; i++) 
{
    [tokanizedTravelPath insertObject: [NSString stringWithFormat: @"%c", [travelPath characterAtIndex:i]] atIndex: i];
}

edited Sep 18 '12 at 11:21

answered Sep 18 '12 at 01:49

Ramy Al Zuhouri

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This code wont work, as the for-condition is false. see my post. – vikingosegundo Sep 18 '12 at 02:27
Oh yes, didn't see it.Edited. – Ramy Al Zuhouri Sep 18 '12 at 11:21

score 1 · Answer 2 · answered Sep 18 '12 at 01:50

1

You can't store unichars in an NSArray*. What exactly are you trying to accomplish? An NSString* is already a great representation for a collection of unichars, and you already have one of those.

answered Sep 18 '12 at 01:50

Lily Ballard

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vikingosegundo · Answer 3 · 2012-09-18T11:49:20.483

I count 3 errors in your code, I explain them at the end of my answer.
First I want to show you a better approach to split a sting into it characters.

While I agree with Kevin that an NSString is a great representation of unicode characters already, you can use this block-based code to split it into substrings and save it to an array.

Form the docs:

enumerateSubstringsInRange:options:usingBlock:
Enumerates the substrings of the specified type in the specified range of the string.

NSString *hwlloWord = @"Hello World";
NSMutableArray *charArray = [NSMutableArray array];
[hwlloWord enumerateSubstringsInRange:NSMakeRange(0, [hwlloWord length])
                              options:NSStringEnumerationByComposedCharacterSequences
                           usingBlock:^(NSString *substring,
                                        NSRange substringRange,
                                        NSRange enclosingRange,
                                        BOOL *stop)
{
    [charArray addObject:substring];
}];
NSLog(@"%@", charArray);

Output:

(
    H,
    e,
    l,
    l,
    o,
    " ",
    W,
    o,
    r,
    l,
    d
)

But actually your problems are of another nature:

An NSArray is immutable. Once instantiated, it cannot be altered. For mutable array, you use the NSArray subclass NSMutableArray.

Also, characterAtIndex does not return an object, but a primitive type — but those can't be saved to an NSArray. You have to wrap it into an NSString or some other representation.

You could use substringWithRange instead.

NSMutableArray *tokanizedTravelPath= [NSMutableArray array];
for (int i=0; i < [hwlloWord length]; ++i) {
    NSLog(@"%@",[hwlloWord substringWithRange:NSMakeRange(i, 1)]);
    [tokanizedTravelPath addObject:[hwlloWord substringWithRange:NSMakeRange(i, 1)]];
}

Also your for-loop is wrong, the for-loop condition is not correct. it must be for (int i=0; i < [travelPath length]; i++)

string tokenizer in ios

3 Answers3