Find second to last word in a string C++

Question

Hi I need to find second to last word in a string. Right now below program is printing the last one.

#include <iostream>
#include <string>

using namespace std;

int main() {
    string text{"some line with text"};
    // find last space, counting from backwards
    int i = text.length() - 2; // last character
    while (i != 0 && !isspace(text[i]))
    {
      --i;
    }
    string lastword = text.substr(i+1); // +1 to skip leading space
    cout << lastword << endl;
    return 0;
}

Output: (Printing last word)

text

Just take the code that you already have and continue iterating until you find the next space. — Rinat Veliakhmedov, Nov 20 '20 at 14:18

score 2 · Answer 1 · answered Nov 20 '20 at 14:00

2

You can split the string into words and hold the previous word before saving the current word.

#include <iostream>
#include <string>
#include <sstream>

int main() {
    std::string text{"some line with text"};
    std::stringstream ss(text);
    std::string previousword, lastword, newword;
    while (ss >> newword) {
        previousword = lastword;
        lastword = newword;
    }
    std::cout << previousword << std::endl;
    return 0;
}

Also note that using using namespace std; is discouraged.

answered Nov 20 '20 at 14:00

MikeCAT

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Beware that this will iterate over the entire text to find the last word. – Rinat Veliakhmedov Nov 20 '20 at 14:15
This would make it faster: `std::stringstream ss ({text.rbegin(), text.rend()});`, then just take the second word. – Mansoor Nov 20 '20 at 14:21
Keep in mind that in this case, the word will be reversed. – Rinat Veliakhmedov Nov 20 '20 at 14:26
1

Then reverse the reversed word: `std::string(secondword.rbegin(), secondword.rend())` – MikeCAT Nov 20 '20 at 14:31

score 1 · Answer 2 · answered Nov 20 '20 at 20:49

You don't need any loops. Just add error checking:

int main() {
  std::string text{ "some line with text" };
  std::size_t pos2 = text.rfind(' ');
  std::size_t pos1 = text.rfind(' ', pos2-1);

  std::cout << text.substr(pos1+1, pos2-pos1-1) << std::endl;
  return 0;
}

Gary Strivin' · Answer 3 · 2020-11-20T14:57:02.747

Just keep counting spaces until you arrive to the word you want or use a stringstream as MikeCAT proposed.

Here there is a function that finds any last word number without having to copy the entire string in a stringstream:

#include <iostream>
#include <string>
using std::string;
using std::cout;
using std::endl;

string getNLastWord(string text, int n)
{
    bool insideAWord = false;
    int wordNum = 0;
    int wordEnd = -1;
    for(int i = text.size() - 1; i > 0; i--)
    {
        if(text[i] != ' ' && !insideAWord)
        {
            wordNum++;
            insideAWord = true;
        }
        else if(text[i] == ' ')
        {
            insideAWord = false;
        }
        if(wordNum == n)
        {
            wordEnd = i;
            break;
        }
    }
    if(wordEnd == -1)
    {
        cout << "There are no " << n << " words from right." << endl;
    }
    else
    {
        int wordStart;
        for(wordStart = wordEnd; wordStart > 0; wordStart--)
        {
            if(text[wordStart] == ' ')
            {
                wordStart++;
                break;
            }
        }
        return text.substr(wordStart,wordEnd+1-wordStart);
    }
    return "";
}

int main() {
    string text = "some text";
    cout << getNLastWord(text,2);
    return 0;
}

Find second to last word in a string C++

3 Answers3