Using erase() in a while loop and segfault C++ - c++

Question

Okay, so I'm having a bit of a problem here. The thing is this code works on a friend's computer but I'm getting segmentation faults when I try to run it.
I am reading a file looking like so:
word 2 wor ord
anotherword 7 ano oth the her erw wor ord
...
And I want to parse every word of the file. The first two words (e.g. word and 2) are to be erased but saving the first one in another variable in the process.
I've looked around a bit on accomplishing this, and I've come up with this half-assed piece of code that seems to work on my friends' computer but not mine.
Dictionary::Dictionary() {
ifstream ip;
ip.open("words.txt", ifstream::in);
string input;
string buf;
vector<string> tokens; // Holds words
while(getline(ip, input)){
if(input != " ") {
stringstream ss(input);
while(ss >> buf) {
tokens.push_back(buf);
}
string werd = tokens.at(0);
tokens.erase(tokens.begin()); // Remove the word from the vector
tokens.erase(tokens.begin()); // Remove the number indicating trigrams
Word curr(werd, tokens);
words[werd.length()].push_back(curr); // Put the word at the vector with word length i.
tokens.clear();
}
}
ip.close();
}
What's the best of of parsing this kind of structure in a file and removing the first two elements but saving the others? As you can see, I'm making a Word object that contains a string and a vector for later use.
Regards
EDIT; It seems to add the first line fine, but on removal of the second element, it crashes with a segmentation fault error.
EDIT; words.txt contain this:
addict 4 add ddi dic ict
sinister 6 ini ist nis sin ste ter
test 2 est tes
cplusplus 7 cpl lus lus plu plu spl usp
Without leading blank spaces or ending blanks. Not that it reads all the way anyway.
Word.cc:
#include <string>
#include <vector>
#include <algorithm>
#include "word.h"
using namespace std;
Word::Word(const string& w, const vector<string>& t) : word(w), trigrams(t) {}
string Word::get_word() const {
return word;
}
unsigned int Word::get_matches(const vector<string>& t) const {
vector<string> sharedTrigrams;
set_intersection(t.begin(),t.end(), trigrams.begin(), trigrams.end(), back_inserter(sharedTrigrams));
return sharedTrigrams.size();
}

Answer 1

First of all, there is error in the number of closing }s in your posted code. If you indent them properly, you will see that your code is:
while(getline(ip, input))
{
if(input != " ")
{
stringstream ss(input);
while(ss >> buf) {
tokens.push_back(buf);
}
}
string werd = tokens.at(0);
tokens.erase(tokens.begin());
tokens.erase(tokens.begin());
Word curr(werd, tokens);
words[werd.length()].push_back(curr);
tokens.clear();
}
}
Assuming that is a small typo in posting, the other problem is that tokens is an empty list when input == " " yet you continue to use tokens as though it has 2 or more items in it.
You can fix that by moving everything inside the if statement.
while(getline(ip, input))
{
if(input != " ")
{
stringstream ss(input);
while(ss >> buf) {
tokens.push_back(buf);
}
string werd = tokens.at(0);
tokens.erase(tokens.begin());
tokens.erase(tokens.begin());
Word curr(werd, tokens);
words[werd.length()].push_back(curr);
tokens.clear();
}
}
I would add further checks to make it more robust.
while(getline(ip, input))
{
if(input != " ")
{
stringstream ss(input);
while(ss >> buf) {
tokens.push_back(buf);
}
string werd;
if ( !tokens.empty() )
{
werd = tokens.at(0);
tokens.erase(tokens.begin());
}
if ( !tokens.empty() )
{
tokens.erase(tokens.begin());
}
Word curr(werd, tokens);
words[werd.length()].push_back(curr);
tokens.clear();
}
}

Answer 2

You forgot to include the initialization of the variable "words" in your code. Just looking at it, I am guessing you are initializing "words" to be a fixed-length array of vectors, but then read a word that is off the end of the array. Bang, you're dead. Add a check to "werd.length()" to ensure it is strictly less than the length of "words".

Answer 3

ifstream ip;
ip.open("words.txt", ifstream::in);
string input;
while(getline(ip, input)){
istringstream iss(input);
string str;
unsigned int count = 0;
if(iss >> str >> count) {
vector<string> tokens { istream_iterator<string>(iss), istream_iterator<string>() }; // Holds words
if(tokens.size() == count)
words[str.length()].emplace_back(str, tokens);
}
}
ip.close();
This is what I used to make it work.