Merging Two Files using C++

ckoniecny · 09-22-2006, 10:41 PM

I have the following two files:
File1:
11 John Doe
33 Jane Doe
55 Steve Smith

File2:
22 Joe Doe
44 Willy Widget

I'm trying to merge the two files to look like:

Output:
11 John Doe
22 Joe doe
33 Jane Doe
44 Willy Widget
55 Steve Smith

Note: I cannot use array's to sort.

This is the code I have thus far:

Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
     ifstream File1, File2;
     string File1_FirstName, File1_LastName;
     string File2_FirstName, File2_LastName;
     int File1_num, File2_num, NumberOne, NumberTwo;
     ofstream outFile;

     File1.open("File1.txt", ios::in);
     File2.open("File2.txt", ios::in);
   
     outFile.open("Output.txt", ios::out);

     

     while (!File2.eof())
     {
          File1 >> File1_num >> File1_FirstName >> File1_LastName;
          NumberOne = File1_num;

          File2 >> File2_num >> File2_FirstName >> File2_LastName;
          while (!File1.eof())
          {
               File1 >> File1_num >> File1_FirstName >> File1_LastName;
               NumberTwo = File1_num;

	       if ( NumberOne > File2_num < NumberTwo )
	       {
	            outFile << NumberOne << '\t' 
                            << FirstName << '\t'
                            << LastName << '\n';
               } 
           }
     }
     return 0;
}

My output is not what I expected, I'm having logic issues. Can anyone point me in the correct direction?

paulsm4 · 09-23-2006, 02:30 AM

Sounds a bit like a homework assignment ;-)

A couple of tips:

1. Are you sure both files are each in sorted order (if you can assume "sorted order", it definitely simplifies your "merge" algorithm)

2. I think the main loop should probably look more like this:

Code:

  while (!File1.eof()) && !File2.eof())
    ...
    <= I'M NOT SURE YOU NEED TO PUT YOUR READS IN SEPARATE, NESTED LOOPS

3. You might be able to get away with reading a whole line at a time (instead of parsing each line into separate variables), then just doing a simple string compare.

4. The basic algorithm (assuming item "1" above) is to read a line from one file, then keep reading lines (and writing) lines from the second file until the next line is "greater" than the line from the first file. Etc...

'Hope that helps .. at least a little bit ..

pankaj99 · 09-23-2006, 04:02 AM

you can do it easily if you know mergesort.
what you are trying to do is 'merging' part in a maergesort.
read about mergesort from any algo book ,
your problem will become trivial.

ckoniecny · 09-23-2006, 09:35 PM

This is what I have so far, but its not working... Whats wrong w/ it??

Code:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
        ifstream File1;
        ifstream File2;
        ofstream outFile;

        string File1_fName, File1_lName;
        string File2_fName, File2_lName;
        int File1_acctNum, File2_acctNum;

        File1.open("file1", ios::in);
        File2.open("file2", ios::in);
        outFile.open("out.txt", ios::out);

        File1 >> File1_acctNum >> File1_fName >> File1_lName;
        File2 >> File2_acctNum >> File2_fName >> File2_lName;
        while (!File1.eof() && !File2.eof())
        {
                if (File2_acctNum > File1_acctNum)
                {
                        outFile << File1_acctNum << '\t' << File1_fName << '\t'
                                << File1_lName << " *\n";
                        outFile << File2_acctNum << '\t' << File2_fName << '\t'
                                << File2_lName << " *\n";
                        File1 >> File1_acctNum >> File1_fName >> File1_lName;
                        File2 >> File2_acctNum >> File2_fName >> File2_lName;
                        cout << File2_acctNum << "\t" << File2_fName << "\t" << File2_lName << endl;
                }
                else if (File1.eof())
                {
                        while (!File2.eof())
                        {
                                outFile << File2_acctNum << '\t' << File2_fName << '\t'
                                        << File2_lName << '\n';
                        }
                }
                else if (File2.eof())
                {
                        while(!File1.eof())
                        {
                                outFile << File1_acctNum << '\t' << File1_fName << '\t'
                                        << File1_lName << '\n';
                        }
                }

        }
        return 0;
}

pankaj99 · 09-24-2006, 03:29 AM

#include <string>
missing at the top.

Matir · 09-26-2006, 09:00 AM

I don't understand your logic in:

Code:

            if (File2_acctNum > File1_acctNum)
                {
                        outFile << File1_acctNum << '\t' << File1_fName << '\t'
                                << File1_lName << " *\n";
                        outFile << File2_acctNum << '\t' << File2_fName << '\t'
                                << File2_lName << " *\n";
                        File1 >> File1_acctNum >> File1_fName >> File1_lName;
                        File2 >> File2_acctNum >> File2_fName >> File2_lName;
                        cout << File2_acctNum << "\t" << File2_fName << "\t" << File2_lName << endl;
                }

This performs no sorting, and in fact ALWAYS prints a line from File1, then a line from File2... essentially, just alternating input.