How can i remove prefixed zeros from NSString

Question

I have a string like "00Welcome", "0000To", "0STACKOVERFLOW", "NOW".

Given a NSString, how can i remove zeros from prefix.

I thought initially to go with CharacterAIndex, but looks like not a good idea.

I have just gone through the below link:

Most efficient way to iterate over all the chars in an NSString

Iteration ??.You can perform iteration. if you get some char != '0' you stop iterating else you rewriting this char to null — vishnuvarthan, Aug 07 '14 at 11:35

score 3 · Answer 1 · answered Aug 07 '14 at 11:18

3

If the zeroes are rare:

while ([myString hasPrefix:@"0"])
    myString = [myString subStringFromIndex:1];

answered Aug 07 '14 at 11:18

gnasher729

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1

This could potentially pollute the autorelease pool, depending on the amount of input and the amount of 0s. – dreamlax Aug 07 '14 at 11:27

dreamlax · Answer 2 · 2014-08-07T11:31:08.393

3

This will remove all 0s from both then beginning and the end using stringByTrimmingCharactersInSet::

NSCharacterSet *charsToTrim = [NSCharacterSet characterSetWithCharactersInString:@"0"];

NSString *input = @"00Welcome";    
NSString *output = [input stringByTrimmingCharactersInSet:charsToTrim];

Using regular expressions:

NSRegularExpression *re = [NSRegularExpression regularExpressionWithPattern:@"^0+"];

NSString *input = @"00Welcome";    
NSString *output = [re stringByReplacingMatchesInString:input
                                                options:0
                                                  range:NSMakeRange(0, [input length])
                                           withTemplate:@""];

edited Aug 07 '14 at 11:31

answered Aug 07 '14 at 11:23

dreamlax

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Thanks for the reply, will it remove only prefix, not suffix? – Whoami Aug 07 '14 at 11:24
1

This will remove from the end too. If you want to remove only from the beginning I will post new code, but it won't be as simple. – dreamlax Aug 07 '14 at 11:25
@Whoami: Added a regular expression method which will remove 0s from just the beginning. gnasher729's is shorter and suitable for small input but may cause problems if you are parsing a lot of text. The regular expression method requires compiling only one regular expression object which you can reuse for all of your input. – dreamlax Aug 07 '14 at 11:34
Yup. Thanks for your valuable Input. You rock always!!. :) – Whoami Aug 07 '14 at 11:55
May i ask can u give bit inside on why gnasher729's solution leads to autorelease pool pollute, so that i can understand? – Whoami Aug 07 '14 at 12:03
@Whoami: For gnasher729's solution, it creates new strings each iteration of the loop. If there are 5 zeroes at the beginning of the input, then gnasher729's solution creates 6 strings, that will all exist in memory at once. E.g., `00000Test`, `0000Test`, `000Test`, `00Test`, `0Test` and `Test`. This isn't a big problem if you are only processing a small number of strings, but if you are processing thousands of strings or the strings you are processing are very large, then it may be using memory very inefficiently. – dreamlax Aug 07 '14 at 12:28

score 3 · Answer 3 · answered Aug 07 '14 at 11:44

NSString *str =@"000034234247236000049327428900000";
NSRange range = [str rangeOfString:@"^0*" options:NSRegularExpressionSearch];
str= [str stringByReplacingCharactersInRange:range withString:@""];

Try this alternative use of regular expressions given by @dreamlax

How can i remove prefixed zeros from NSString

3 Answers3