Referencing members of an object within a class type vector

Question

Ok guys this problem has been bugging me all day and I cant seem find a solution. I know Its a long post but I would be very grateful for any help you can offer. I am working on a chatbot program that reads in from a .dat file to populate a library of keywords. Taking an object orientated approach I defined a class called "Keyword", the class definition is shown below:

class Keyword
{
public:   
    //_Word holds keyword 
    vector<string> _Word;
    //_Resp holds strings of responses
    vector<string> _Resp;
    //_Antymn holds words that are the opposite to keyword
    vector<string> _Antymn;

    // Constructor
    Keyword()
    {
        // Clears members when new instance created
        _Word.clear();
        _Resp.clear();
        _Antymn.clear();
    }
};

Therefore every time a new keyword is found in the .dat file, a new instance of the class keyword must be created. To store all these instances of keyword I create another vector but this time of type Keyword and call it library:

typedef vector<Keyword> Lib;
Lib library;// this is the same as saying vector<Keyword> library

Now this is the problem I have: After a user inputs a string I need to check if that string contains a keyword from the library i.e. I need to see if the string in _Word appears in the user input. Looking at it from a hierarchy of vectors you have:

The top level --> libary //*starting point
                 --> Keyword
                    --> _Word
                      -->"A single string" <-- I want to reference this one
                    --> _Resp
                      -->"Many strings"
                    --> _Antymn
                      -->"Many strings"

Phew! I hope that made sense. This is the code I started to write:

size_t User::findKeyword(Lib *Library)
{
    size_t found;
    int count = 0;

    for(count = 0; count<Library->size(); count++)
    {
      found = _Input.find(Library->at(count)); // this line needs to reference _Word from each keyword instance within library
      if(found!= string.npos)
        return found;
    }

    return 0;
}

I have also tried to use the "operator[]" method but that doesnt seem to do what I want either. Does anyone have any idea ? I would be very suprised if it couldn't be done. Thank you in advance.

Make it: found = _Input.find(Library->at(count)._Word); to access the member variable _Word — xQuare
– xQuare, Commented Aug 24, 2012 at 17:03
why is _word a vector? If you are only storing one keyword per instance of Keyword then it should just be of type string. — Charlie
– Charlie, Commented Aug 24, 2012 at 17:05
Note that names beginning with an underscore followed by a capital letter are reserved to the implementation. Don't use them. — Pete Becker
– Pete Becker, Commented Aug 24, 2012 at 17:05
Hey Papergay, I have tried this before posting but it kept throwing me an error. Could it be down to what Charlie has said ? — Edward Paul
– Edward Paul, Commented Aug 24, 2012 at 17:08
@Papergay: You can make your comment an answer. I would upvote it. — thb
– thb, Commented Aug 24, 2012 at 17:09

pmr · Accepted Answer · 2012-08-24 17:20:42Z

3

A bunch of issues first:

identifiers beginning with an underscore followed by a capital letter are reserved in any namespace
the clear() call in the Keyword constructor are pointless and possibly harmful to optimization

Why is word_ a vector? I though it is one keyword.

struct Keyword
{
    // real words as identifiers, no underscores 
    //anywhere if they are public
    std::string word;
    std::vector<std::string> respones;
    std::vector<std::string> antonym;
};


typedef std::vector<Keyword> Lib;



/// finding a keyword
#include <algorithm>

Lib::iterator findKeyword(const Lib& l, const std::string& x) {
  return std::find_if(begin(l), end(l), 
                      [](const Keyword& kw) { return kw.word == x; })
  // if stuck on non C++11 compiler use a Functor
}

edited Aug 24, 2012 at 17:20

answered Aug 24, 2012 at 17:13

pmr

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2 Comments

Edward Paul Over a year ago

@pmr-thank you for your help. I have now removed the underscores from the class members. I originally used them to differentiate between local variables and class members. The clear() method was only included to initialise the vectors. Isnt this necessary ? Thank you.

pmr Over a year ago

@EdwardPaul A good convention is m_membername or membername_. It is important for private members to avoid ambiguity between a member function with the same name, e.g. the getter size() and the private member size_. The vector::clear is not necessary. A default constructed vector is empty. It also looks like you have using namespace std in a header. This is also bad.

xQuare · Accepted Answer · 2012-08-24 17:21:46Z

2

You have to change your code to this:

for(count = 0; count<Library->size(); count++)
{
    for(int j = 0; j < Library->at(count)._Word.size(); ++j){
        found = _Input.find(Library->at(count)._Word[j]);
                                              ^^^^^^^^^
        if(found!= string.npos)
             return found;
    }
}

in order to access the member variable and to iterate through your vector of strings. Library->at(count) is an object of class the Keyword. I assume that _Input.find() takes a string as argument.

If your Keyword instance stores just one keyword, you might as well change it to string _Word, so that you wold not need the second loop.

for(count = 0; count<Library->size(); count++)
{
    found = _Input.find(Library->at(count)._Word);
    if(found!= string.npos)
        return found;
}

And to enforce the other comments: you should not use the preliminary _-underscore in your variable names since they are reserved by the implementation.

edited Aug 24, 2012 at 17:21

answered Aug 24, 2012 at 17:09

xQuare

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7 Comments

Edward Paul Over a year ago

Thank you so much! _Input.find() does take a string as an argument. I was missing the _Word[j] piece off the end.

pmr Over a year ago

This is actively harmful. vector::at will make an out-of-bounds check and throw and is only recommended for debugging. So is rewriting std::find or unnecessary passing of pointers instead of references.

xQuare Over a year ago

Im not sure, but can you even do Library->[index] ? Or how do you call that operator with pointers?

xQuare Over a year ago

Btw, you should not neglect what pmr is pointing out.

pmr Over a year ago

@Papergay No, you can do Library->operator[](index);

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