Splitting a string by some delimiter is a very common task. For example, we have a comma-separated list of items from a file and we want individual items in an array.
Almost all programming languages, provide a function split a string by some delimiter.
In C:
// Splits str[] according to given delimiters. // and returns next token. It needs to be called // in a loop to get all tokens. It returns NULL // when there are no more tokens. char * strtok(char str[], const char *delims);
C
// A C/C++ program for splitting a string// using strtok()#include <stdio.h>#include <string.h>int main(){ char str[] = "Geeks-for-Geeks"; // Returns first token char *token = strtok(str, "-"); // Keep printing tokens while one of the // delimiters present in str[]. while (token != NULL) { printf("%s\n", token); token = strtok(NULL, "-"); } return 0;} |
Output: Geeks
for
Geeks
Time complexity : O(n)
Auxiliary Space: O(n)
In C++
Note: The main disadvantage of strtok() is that it only works for C style strings.
Therefore we need to explicitly convert C++ string into a char array.
Many programmers are unaware that C++ has two additional APIs which are more elegant
and works with C++ string.
Method 1: Using stringstream API of C++
Prerequisite: stringstream API
Stringstream object can be initialized using a string object, it automatically tokenizes strings on space char. Just like “cin” stream stringstream allows you to read a string as a stream of words. Alternately, we can also utilise getline function to tokenize string on any single character delimiter.
Some of the Most Common used functions of StringStream. clear() — flushes the stream str() — converts a stream of words into a C++ string object. operator << — pushes a string object into the stream. operator >> — extracts a word from the stream.
The code below demonstrates it.
C++
#include <bits/stdc++.h>using namespace std;// A quick way to split strings separated via spaces.void simple_tokenizer(string s){ stringstream ss(s); string word; while (ss >> word) { cout << word << endl; }}// A quick way to split strings separated via any character// delimiter.void adv_tokenizer(string s, char del){ stringstream ss(s); string word; while (!ss.eof()) { getline(ss, word, del); cout << word << endl; }}int main(int argc, char const* argv[]){ string a = "How do you do!"; string b = "How$do$you$do!"; // Takes only space separated C++ strings. simple_tokenizer(a); cout << endl; adv_tokenizer(b, '$'); cout << endl; return 0;} |
Output : How
do
you
do!
Time Complexity: O(n)
Auxiliary Space:O(n)
Where n is the length of the input string.
Method 2: Using C++ find() and substr() APIs.
Prerequisite: find function and substr().
This method is more robust and can parse a string with any delimiter, not just spaces(though the default behavior is to separate on spaces.) The logic is pretty simple to understand from the code below.
C++
#include <bits/stdc++.h>using namespace std;void tokenize(string s, string del = " "){ int start, end = -1*del.size(); do { start = end + del.size(); end = s.find(del, start); cout << s.substr(start, end - start) << endl; } while (end != -1);}int main(int argc, char const* argv[]){ // Takes C++ string with any separator string a = "How$%do$%you$%do$%!"; tokenize(a, "$%"); cout << endl; return 0;} |
Output: How
do
you
do
!
Time Complexity: O(n)
Auxiliary Space:O(1)
Where n is the length of the input string.
Method 3: Using temporary string
If you are given that the length of the delimiter is 1, then you can simply use a temp string to split the string. This will save the function overhead time in the case of method 2.
C++
#include <iostream>using namespace std;void split(string str, char del){ // declaring temp string to store the curr "word" upto del string temp = ""; for(int i=0; i<(int)str.size(); i++){ // If cur char is not del, then append it to the cur "word", otherwise // you have completed the word, print it, and start a new word. if(str[i] != del){ temp += str[i]; } else{ cout << temp << " "; temp = ""; } } cout << temp;}int main() { string str = "Lazyroar_for_Lazyroar"; // string to be split char del = '_'; // delimiter around which string is to be split split(str, del); return 0;} |
Lazyroar for Lazyroar
Time complexity : O(n)
Auxiliary Space: O(n)
In Java :
In Java, split() is a method in String class.
// expregexp is the delimiting regular expression; // limit is the number of returned strings public String[] split(String regexp, int limit); // We can call split() without limit also public String[] split(String regexp)
Java
// A Java program for splitting a string// using split()import java.io.*;public class Test{ public static void main(String args[]) { String Str = new String("Geeks-for-Geeks"); // Split above string in at-most two strings for (String val: Str.split("-", 2)) System.out.println(val); System.out.println(""); // Splits Str into all possible tokens for (String val: Str.split("-")) System.out.println(val); }} |
Output:
Geeks for-Geeks Geeks for Geeks
Time complexity : O(n)
Auxiliary Space: O(1)
In Python:
The split() method in Python returns a list of strings after breaking the given string by the specified separator.
// regexp is the delimiting regular expression; // limit is limit the number of splits to be made str.split(regexp = "", limit = string.count(str))
Python3
line = "Geek1 \nGeek2 \nGeek3"print(line.split())print(line.split(' ', 1)) |
Output:
['Geek1', 'Geek2', 'Geek3'] ['Geek1', '\nGeek2 \nGeek3']
Time Complexity : O(N), since it just traverse through the string finding all whitespace.
Auxiliary Space : O(1), since no extra space has been used.
This article is contributed by Aarti_Rathi and Aditya Chatterjee. If you like Lazyroar and would like to contribute, you can also write an article and mail your article to review-team@neveropen.co.za. See your article appearing on the Lazyroar main page and help other Geeks.
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