Solved

URGENT:  iterating through Hash Table

Posted on 2003-11-04
5
410 Views
Last Modified: 2010-04-01
I have an STL hashTable keyed on strings and the objects are custom objects.  What is the best way to go and get each pair (I need to ouptut both the key and value together).
0
Comment
Question by:jjacksn
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
5 Comments
 
LVL 4

Expert Comment

by:nil_dib
ID: 9684988
sample for map (hashTable should be similar) :

#pragma warning(disable:4786)

#include <iostream>
#include <string>
#include <map>

using namespace std ;

typedef map<string, int> STRING2INT;

void main()
{
    STRING2INT MyMap;
    STRING2INT::iterator MyIterator;
    string MyBuffer;

    // print the maximum number of <key,data> pairs that MyMap can hold
    cout << "MyMap is capable of holding " << MyMap.max_size()
         << " <string,int> pairs" << endl;

    if(!MyMap.empty())
        cout << "MyMap has " << MyMap.size() << " entries" << endl;
    else
        cout << "MyMap is empty" << endl;
        cout << "Entering new entries in MyMap" << endl;
    // Fill in MyMap with the months of the year, mapped to their number
    // January - 1, February - 2, etc. using operator[].
    MyMap["January"] = 1;
    MyMap["February"] = 2;
    MyMap["March"] = 3;
    MyMap["April"] = 4;
    MyMap["May"] = 5;
    MyMap["June"] = 6;
    MyMap["July"] = 7;
    MyMap["August"] = 8;
    MyMap["September"] = 9;
    MyMap["October"] = 10;
    MyMap["November"] = 11;
    MyMap["December"] = 12;

    if(!MyMap.empty())
        cout << "MyMap has " << MyMap.size() << " entries" << endl;
    else
        cout << "MyMap is empty" << endl;

    // Ask the user for a month of the year and print the number
    // that corresponds to the month entered
    //MyIterator = MyMap.end();
    while(MyIterator == MyMap.end()){
        cout << "Enter a Month :";
        cin >> MyBuffer;
        if((MyIterator = MyMap.find(MyBuffer)) != MyMap.end())
            cout << (*MyIterator).first << " is Month Number "
                 << (*MyIterator).second << endl;
        else
            cout << "Enter a Valid Month (example: March)" << endl;
    }

    // empty MyMap - note that clear simply calls erase(begin(),end());
    MyMap.clear();

    if(!MyMap.empty())
        cout << "MyMap has " << MyMap.size() << " entries" << endl;
    else
        cout << "MyMap is empty" << endl;
        cout << "Entering new entries in MyMap" << endl;
    // Fill MyMap with the days of the week, each mapped to an int
    MyMap["Monday"] = 1;
    MyMap["Tuesday"] = 2;
    MyMap["Wednesday"] = 3;
    MyMap["Thursday"] = 4;
    MyMap["Friday"] = 5;
    MyMap["Saturday"] = 6;
    MyMap["Sunday"] = 7;

    if(!MyMap.empty())
        cout << "MyMap has " << MyMap.size() << " entries" << endl;
    else
        cout << "MyMap is empty" << endl;

    // Ask the user for a day of the week and print the number
    // that corresponds to the day entered
    MyIterator = MyMap.end();
    while(MyIterator == MyMap.end()){
        cout << "Enter a Day of the Week:";
        cin >> MyBuffer;
        if((MyIterator = MyMap.find(MyBuffer)) != MyMap.end())
            cout << (*MyIterator).first << " is Day Number "
                 << (*MyIterator).second << endl;
        else
            cout <<"Enter a Valid Day of the Week(example: Monday)"<< endl;
    }
// Now clear MyMap again - this time using erase instead of clear
    MyMap.erase(MyMap.begin(), MyMap.end());

    if(!MyMap.empty())
        cout << "MyMap has " << MyMap.size() << " entries" << endl;
    else
        cout << "MyMap is empty" << endl;

}



nil_dib
0
 
LVL 5

Author Comment

by:jjacksn
ID: 9685019
am I correct in thinking that If I make an iterator, .first will contain the key and .second will contain the value?
0
 
LVL 4

Accepted Solution

by:
nil_dib earned 300 total points
ID: 9685101
no! look at this sample:

#pragma warning(disable:4786)

#include <iostream>
#include <string>
#include <map>

using namespace std;


typedef map<int, string, less<int> > INT2STRING;

void main()
{
// 1. Create a map of ints to strings
    INT2STRING theMap;
    INT2STRING::iterator theIterator;


// Fill it with the digits 0 - 9, each mapped to its string counterpart
// Note: value_type is a pair for maps...
    theMap.insert(INT2STRING::value_type(0,"Zero"));
    theMap.insert(INT2STRING::value_type(1,"One"));
    theMap.insert(INT2STRING::value_type(2,"Two"));
    theMap.insert(INT2STRING::value_type(3,"Three"));
    theMap.insert(INT2STRING::value_type(4,"Four"));
    theMap.insert(INT2STRING::value_type(5,"Five"));
    theMap.insert(INT2STRING::value_type(6,"Six"));
    theMap.insert(INT2STRING::value_type(7,"Seven"));
    theMap.insert(INT2STRING::value_type(8,"Eight"));
    theMap.insert(INT2STRING::value_type(9,"Nine"));

            
  for (theIterator=theMap.begin();theIterator!=theMap.end();theIterator++)
     cout << "key " << (*theIterator).first << " value." << (*theIterator).second << endl;
}


acces to key and value via ONE iterator ((*theIterator).first and (*theIterator).second)

nil_dib
0
 
LVL 5

Author Comment

by:jjacksn
ID: 9685197
Isn't that exactly the question I just asked?  
0
 
LVL 4

Expert Comment

by:nil_dib
ID: 9685215
oh, sure it is!
sorry, missunderstoud your comment ...

nil_dib
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

What is C++ STL?: STL stands for Standard Template Library and is a part of standard C++ libraries. It contains many useful data structures (containers) and algorithms, which can spare you a lot of the time. Today we will look at the STL Vector. …
Introduction This article is a continuation of the C/C++ Visual Studio Express debugger series. Part 1 provided a quick start guide in using the debugger. Part 2 focused on additional topics in breakpoints. As your assignments become a little more …
The goal of the tutorial is to teach the user how to use functions in C++. The video will cover how to define functions, how to call functions and how to create functions prototypes. Microsoft Visual C++ 2010 Express will be used as a text editor an…
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

749 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question