CODEWITHSUNDEEP
dartflutter
deantawonezvi
deantawonezvi

Reputation: 1087

How to get the last n-characters in a string in Dart?

How do I get the last n-characters in a string?

I've tried using:

var string = 'Dart is fun';
var newString = string.substring(-5);

But that does not seem to be correct

Upvotes: 80

Views: 65561

Answers (7)

Driexus
Driexus

Reputation: 38

Leaving these extension methods here to be useful for anyone. I do not know if they are in some dart standard library, but I could not find them.

extension Substrings on String {

  /// Takes the first n characters.
  String takeFirst(int n) {
    final int end = n > length ? length : n;
    return substring(0, end);
  }

  /// Takes the last n characters.
  String takeLast(int n) {
    final int start = n > length ? 0 : length - n;
    return substring(start, length);
  }

  /// Drops the first n characters.
  String dropFirst(int n) {
    return n > length ? "" : substring(length - n, length);
  }

  /// Drops the last n characters.
  String dropLast(int n) {
    return n > length ? "" : substring(0, length - n);
  }
}

In your case you would want to use

string.takeLast(5);

Upvotes: 1

M.J Jang
M.J Jang

Reputation: 11

extension Operation on String? {
  String lastChars(int n) {
    if (this == null) return '';
    return this!.characters.takeLast(n).string;
  }
}

Maybe you can try this:

When n < str.length, eg: 'object'.lastChars(2), you get ct;

when n >= str.length, and you get the whole string, eg: 'object'.lastChars(10), you get object.

Upvotes: 1

Komolafe Ezekiel dare
Komolafe Ezekiel dare

Reputation: 115

I wrote my own solution to get any no of last n digits from a string of unknown length, for example the 5th to the last digit from an n digit string,

 String bin='408 408 408 408 408 1888';// this is the your string

  // this function is to remove space from the string and then reverse the 
 string, then convert it to a list
  List reversed=bin.replaceAll(" ","").split('').reversed.toList();

 //and then get the 0 to 4th digit meaning if you want to get say 6th to last digit, just pass 0,6 here and so on. This second reverse function, return  the string to its initial arrangement
  var list = reversed.sublist(0,4).reversed.toList();
  var concatenate = StringBuffer();
  
  // this function is to convert the list back to string 
  list.forEach((item){
    concatenate.write(item);
  });

  print(concatenate);// concatenate is the string you need

Upvotes: 0

CopsOnRoad
CopsOnRoad

Reputation: 267784

Create an extension:

extension E on String {
  String lastChars(int n) => substring(length - n);
}

Usage:

var source = 'Hello World';
var output = source.lastChars(5); // 'World'

Upvotes: 35

Radek
Radek

Reputation: 1630

var newString = string.substring((string.length - 5).clamp(0, string.length));

note: I am using clamp in order to avoid Value Range Error. By that you are also immune to negative n-characters if that is somehow calculated.

In fact I wonder that dart does not have such clamp implemented within the substring method.

If you want to be null aware, just use:

var newString = string?.substring((string.length - 5).clamp(0, string.length));

Upvotes: 5

stevenspiel
stevenspiel

Reputation: 5999

While @Alexandre Ardhuin is correct, it is important to note that if the string has fewer than n characters, an exception will be raised:

Uncaught Error: RangeError: Value not in range: -5

It would behoove you to check the length before running it that way

String newString(String oldString, int n) {
  if (oldString.length >= n) {
    return oldString.substring(oldString.length - n)
  } else {
    // return whatever you want
  }
}

While you're at it, you might also consider ensuring that the given string is not null.

oldString ??= '';

If you like one-liners, another options would be:

String newString = oldString.padLeft(n).substring(max(oldString.length - n, 0)).trim()

If you expect it to always return a string with length of n, you could pad it with whatever default value you want (.padLeft(n, '0')), or just leave off the trim().

At least, as of Dart SDK 2.8.1, that is the case. I know they are working on improving null safety and this might change in the future.

Upvotes: 14

Alexandre Ardhuin
Alexandre Ardhuin

Reputation: 76253

var newString = string.substring(string.length - 5);

Upvotes: 133

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