Iterators

This is a discussion on Iterators within the C++ Programming forums, part of the General Programming Boards category; Why does this code print what's in before twice?: Code: void element::printelementsplusgroupbefore (void) { map<std::string, int> temp; vector<map<std::string, int> >::iterator ...

  1. #1
    MFC killed my cat! manutd's Avatar
    Join Date
    Sep 2006
    Location
    Boston, Massachusetts
    Posts
    870

    Iterators

    Why does this code print what's in before twice?:
    Code:
    void element::printelementsplusgroupbefore (void)
    {
        map<std::string, int> temp;
        vector<map<std::string, int> >::iterator itr;
        map<std::string, int>::iterator mitr;
        int i = 1;
        for (itr = before.begin(); itr != before.end(); itr++)
        {
            temp = *itr;
            cout << "Plus group: " << i << endl;
            for (mitr = temp.begin(); mitr != temp.end(); ++mitr)
            {
                cout << "Element: " << mitr->first << " Count: " << mitr->second << endl;
            }
            temp.clear();
            i++;
        }
        cout << endl;
    }
    I give the input (processed elsewhere) of this:
    H2O2+C->*doesn't matter, not printed by this function*

    This function prints:

    Plus Group: 1
    Element: H Count: 2
    Element: O Count: 2
    Plus Group: 2
    Element: C Count: 1

    Plus Group: 1
    Element: H Count: 2
    Element: O Count: 2
    Plus Group: 2
    Element: C Count: 1

    Why does it print twice?
    Silence is better than unmeaning words.
    - Pythagoras
    My blog

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    Location
    Singapore
    Posts
    23,618
    Could it be a problem with the before member variable?
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
    MFC killed my cat! manutd's Avatar
    Join Date
    Sep 2006
    Location
    Boston, Massachusetts
    Posts
    870
    Here's before:
    Code:
    vector<map<std::string, int> > before;
    Initialized with this function:
    Code:
    vector<map<std::string, int> > element::findelementplusgroupbefore(int* whereyield)
    {
        vector<map<std::string, int> > creed;
        map<std::string, int> need;
        std::string feed;
        for (int i = 0; i < formula.size(); i++)
        {
            if (formula[i] == '+')
            {
                creed.push_back(need);
                need.clear();
                feed.clear();
            }
            else if (isupper(formula[i]))
            {
                if(islower(formula[i+1]))
                {
                    if (isdigit(static_cast<int>(formula[i+2])))
                    {
                        feed += formula[i];
                        feed += formula[i+1];
                        need.insert(make_pair(feed, (static_cast<int>(formula[i+2])) - 48));
                        i += 2;
                    }
                    else
                    {
                        feed += formula[i];
                        feed += formula[i+1];
                        need.insert(make_pair(feed, 1));
                        i++;
                    }
                }
                else
                {
                    if (isdigit(static_cast<int>(formula[i+1])))
                    {
                        feed += formula[i];
                        need.insert(make_pair(feed, (static_cast<int>(formula[i+1])) - 48));
                        i++;
                    }
                    else
                    {
                        feed += formula[i];
                        need.insert(make_pair(feed, 1));
                    }
                }
                feed.clear();
            }
            else if (formula[i] == '-' && formula[i+1] == '>')
            {
                *whereyield = (formula[i+1]) - 57;
                break;
            }
        }
        creed.push_back(need);
        return creed;
    }
    And the constructor:
    Code:
    element::element()
    {
        cout << "Enter a formula:" << endl;
        cin >> formula;
        if (checkyield(formula))
        {
            before = findelementplusgroupbefore(&whereyield);
            after = findelementplusgroupafter(whereyield);
            printall();
        }
    }
    Silence is better than unmeaning words.
    - Pythagoras
    My blog

  4. #4
    (?<!re)tired Mario F.'s Avatar
    Join Date
    May 2006
    Location
    Angola
    Posts
    7,909
    Plus Group: 1
    The fact 1 is output through a counter that is not getting incremented, leads me to believe you are calling this function twice. The problem is somewhere else. Not within that code.
    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  5. #5
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    Location
    Singapore
    Posts
    23,618
    I think that you should come up with the smallest and simplest compilable program that demonstrates the problem.

    Oh, and I agree with Mario F. - the function is probably being called twice.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  6. #6
    MFC killed my cat! manutd's Avatar
    Join Date
    Sep 2006
    Location
    Boston, Massachusetts
    Posts
    870
    Thanks Mario, that was the problem. In another part, a relic was calling that function.
    Silence is better than unmeaning words.
    - Pythagoras
    My blog

Popular pages Recent additions subscribe to a feed

Similar Threads

  1. vector of strings with iterators.
    By Mario F. in forum C++ Programming
    Replies: 6
    Last Post: 05-31-2006, 12:12 PM
  2. Using reverse iterators in algorithms
    By 0rion in forum C++ Programming
    Replies: 1
    Last Post: 02-27-2006, 02:19 AM
  3. Writing Iterators...
    By DeepBlackMagic in forum C++ Programming
    Replies: 6
    Last Post: 05-29-2003, 09:31 PM
  4. accessing vector elements: iterators are faster?
    By Captain Penguin in forum C++ Programming
    Replies: 1
    Last Post: 11-28-2002, 01:27 PM
  5. Generic Progpammimg Iterators
    By rip1968 in forum C++ Programming
    Replies: 7
    Last Post: 08-06-2002, 10:20 AM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21