C++ Program to Split a String Into a Number of Sub-Strings

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++

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.

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. 

#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;
    }
}

int main(int argc, char const* argv[])
{
    string a = "How do you do!";
    // Takes only space separated C++ strings.
    simple_tokenizer(a);
    cout << endl;
    return 0;
}

Output : How 
     do 
     you
     do!

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.

#include <bits/stdc++.h>
using namespace std;

void tokenize(string s, string del = " ")
{
    int start = 0;
    int end = s.find(del);
    while (end != -1) {
        cout << s.substr(start, end - start) << endl;
        start = end + del.size();
        end = s.find(del, start);
    }
    cout << s.substr(start, end - start);
}
int main(int argc, char const* argv[])
{
    // Takes C++ string with any separator
    string a = "Hi$%do$%you$%do$%!";
    tokenize(a, "$%");
    cout << endl;

    return 0;
}

Output: Hi 
    do 
    you
    do
    !

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.

#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 = "geeks_for_geeks";    // string to be split
     char del = '_';    // delimiter around which string is to be split
  
      split(str, del);
    
    return 0;
}

geeks for geeks

Time complexity: O(n) where n is the length of the string.
Auxiliary Space: O(1)