CODEWITHSUNDEEP
c++stringfunctionvector
LukaSsS
LukaSsS

Reputation: 120

Getting some junk returned by a function

I participated in different coding contests and therefore cant use python cause it's too slow on execution time, but i really like the input.split() thing, so i tried to implement my own split. Here is what i came up with:

#include <iostream>
#include <vector>
#include <stack>

using namespace std;

vector<string> splt(string s){
    vector<string> ans={};
    for(int i=0;i<s.size();i++){
        string str="";
        while(s[i]!=' '){
            str+=s[i];
            i++;
        }
        ans.push_back(str);
    }
    return ans;
}

int main(){
    string s;
    getline(cin, s);
    vector<string> ans=splt(s);
    for(auto i:ans)
        cout<<i<<", ";
}

But the vector returned by the function often(but no always) has some junk at the end. Would appreciate any help with correcting my code, as well as some other impementation of splitting a string into an array.

P.S. Sorry if my English is bad, im from Russia and haven't even finished school :)

Upvotes: 4

Views: 249

Answers (4)

Ketzu
Ketzu

Reputation: 691

Your while loop does not check for the end of the string, so if you reach the last space in your string, it will not stop at the last character.

while(s[i]!=' ' && i<s.size()){

It is probably smarter to use the solution using streams from the other answer, or use the find method of the string class and the substring method. Example:

vector<string> splt(string s){
    vector<string> ans={};
    size_t found = s.find_first_of(' ');
    size_t last = 0;
    while(found!=string::npos){
        ans.push_back(s.substr(last,found));
        last = found+1;
        found = s.find_first_of(' ',found+1);
    }
    ans.push_back(s.substr(last,s.size()));
    return ans;
}

Upvotes: 0

Destructor
Destructor

Reputation: 523

while(s[i]!=' '){
        str+=s[i];
        i++;
}

The above code part doesn't check for the boundary of s. While doing i++ you might go over the boundary of the string. So check if i == s.size() and break from the loop.

Upvotes: 2

molbdnilo
molbdnilo

Reputation: 66371

Your inner loop doesn't stop at the end of the string, only when it encounters a space character.
Thus, if your input doesn't end with a space, you're going to index outside the string and have undefined behaviour.
(And when it works, contiguous space characters will result in empty strings, which you probably don't want.)

The most straightforward way to split on whitespace is to use a stream:

#include <sstream>

vector<string> split(string s){
    vector<string> ans;
    istringstream ss(s);
    string word;
    while (ss >> word)
        ans.push_back(word);
    return ans;
}

or

#include <algorithm>
#include <iterator>
#include <sstream>

vector<string> split(string s){
    vector<string> ans;
    istringstream ss(s);
    copy(istream_iterator<string>(ss), istream_iterator<string>(), back_inserter(ans));
    return ans;
}

Upvotes: 2

eerorika
eerorika

Reputation: 238351

In this loop:

    while(s[i]!=' '){
        str+=s[i];
        i++;
    }

You never check whether i is outside the bounds of s and as long as there isn't a ' ' there, i will be incremented beyond the boundary, and the string will be accessed outside of bounds. The behaviour of accessing the string outside of bounds is undefined.

Upvotes: 8

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