Reading strings from file into array

Question

Hey. I'm trying to read strings into an array from a file that contains a list of words. This is so that I can check to see if strings are a real word by seing is they exist inside my array. I have everything working except the compare. My binary search even passes by the word in question. When it compares the two words which are exactly the same, it still returns false. I think the problem is probably in the way I am pulling the words in because the string.compare() function works fine normally. Here is that code. I would love some help. Thanks.

  ifstream dictFile;
  dictFile.open("dictionary.txt");
  if (!dictFile) // testing if file open
    {
      cout << "Error opening dictionary file" << endl;
    }
  int index = 0; // dictionary must progress start at line 1
  while(!dictFile.eof())
    {
      getline(dictFile,dictionary[index]);
      index++;
    }
  dictFile.close();

Is there anything just plain wrong about how I am doing this?

EDIT Here is the comparison code as well

bool database::is_word(string word)
{
  int ii;
  int comp;
  int min = 0;
  int max = dictSize;
  // this will go into the dictionary and look for the word
  // it uses a binary search pattern
while (min<=max)
    {
      ii = (min+max)/2;
      comp = word.compare(dictionary[ii]);
      cout <<dictionary[ii];
      if (comp==0)
    {
      cout << word<< " is a word!" << endl;
      return 1;
    }
      else if (comp < 0)
    {
      max = ii-1;
    }
      else
    {
      min = ii+1;
      }
      }
 cout << word << " is NOT a word!" << endl;
  return 0;
}

Is getline retrieving the word as well as the \n (return) at the end of the line? If so, the compare could think that the words are different because it would loook like "word" != "word\n". Just a thought. — Tyler Ferraro
– Tyler Ferraro, Commented Apr 26, 2011 at 16:34
Can you add in the code that you use for string comparison? It's probably an issue with whatever function you're calling for comparison rather than a file read problem itself. — photoionized
– photoionized, Commented Apr 26, 2011 at 16:45
Hmm... how are you calling is_word and are you sure that your dictSize variable is valid? I just wrote some quick test code and it works perfectly for me. — photoionized
– photoionized, Commented Apr 26, 2011 at 17:28

user2100815 · Accepted Answer · 2011-04-26 16:34:42Z

1

Not the eof() function again! You want:

while( getline(dictFile,dictionary[index]) ) {
  index++;
}

(assuming dictionary is something sensible, which it might not be) because eof() does not predict if the next read will work.

And where oh where are people picking up this use of eof() from? It's like a disease!

answered Apr 26, 2011 at 16:34

user2100815

Sign up to request clarification or add additional context in comments.

3 Comments

Rusty Over a year ago

Saw it somewhere... I will immediately make a mental note not to use it again. However, this fix produces the same error.

André Caron Over a year ago

I prefer writing this as: for ( string line; getline(input,line); ) { ... } because it is more idiomatic, allows post-processing of line contents and is uniform across container types.

user2100815 Over a year ago

@Andre I can't say that I see it as idiomatic - I expect a for loop to loop from one known value to another, not to be indeterminate.

user223264 · Accepted Answer · 2011-04-26 17:49:58Z

0

This is how I'd do the whole program, if my goal were terseness and not performance.

// read the dictionary 

vector<string> dictionary;
{
  ifstream dictionary_file("dictionary.txt");
  istream_iterator<string> begin(dictionary_file);
  istream_iterator<string> end;
  while( begin != end )
    dictionary.push_back( *begin++ );
  sort( dictionary.begin(), dictionary.end() );
}

// read the input file and test against the dictionary

{
  ifstream input_file("input.txt");
  istream_iterator<string> begin(input_file);
  istream_iterator<string> end;
  while( begin != end )
  {
    string input = *begin++;
    vector<string>::iterator it = lower_bound( dictionary.begin(), dictionary.end(), input );
    if( it != dictionary.end() && *it == input )
      cout << input << " found!" << endl;
    else
      cout << input << " not found!" << endl;
  }
}

answered Apr 26, 2011 at 17:49

user223264

2 Comments

André Caron Over a year ago

Using a std::set would probably give you much better performance, make the intent clearer, as well as simplify it: dictionary.find(word) != dictionary.end() is much clearer than using lower_bound() on a vector!

user223264 Over a year ago

You are right that std::set would read more clearly, but you are wrong that it would have better performance. std::set and a sorted std::vector should have exactly the same performance when searching for an item.

Collectives™ on Stack Overflow

Reading strings from file into array

2 Answers 2

3 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related