I/O with strings

[kristentx]

The object of my program is to read one line from a file, read a line from another file, compare the two and if file 1 is smaller than file 2, then it is supposed to write from file 1 to the output line and read a new line from file 1. Otherwise, it writes the line from file 2 to the output file and reads a new line from file 2. The program is supposed to do this while the end of neither file 1 of file 2 has been reached. Then if there is any line in file 1 or file 2 that still has not been written to the output file, the program should write those lines. Here is my code:

#include <iostream>
#include <iomanip>
#include <cmath>
#include <cstdlib>     
#include <fstream>  
#include <cstring>  
#include <string>

using namespace std;

int openFile(fstream& f, fstream& f1, fstream& f2);//function to open the files
void readWriteData(fstream& f, fstream& f1, fstream& f2);//function to read and write data


int main()
{
    fstream outFile; //output
    fstream inFile1;//input
    fstream inFile2;//input
    
    openFile(outFile, inFile1, inFile2);
    cin.get();
    return 0;    
}


int openFile(fstream& outFile, fstream& inFile1, fstream& inFile2)
{
    char outName[50];//storage of user input filename for the data file that is to be written to
    char inName1[50];//storage of user input filename for the first data file that is to be read from
    char inName2[50];//storage of user input filename for the second data file that is to be read from
    
    cout << "Please type the name of the first input file, including the extension: ";//requests user input of filename
    cin >> inName1;
    cout <<'\n';
    inFile1.open(inName1, ios::in);   
    if (inFile1.fail())//if file cannot be opened, a message will display
        {
            cerr << "Could not open " << inName1 << "!" << endl;
            return EXIT_FAILURE;
        }
    
    cout << "Please type the name of the second input file, including the extension: ";//requests user input of filename
    cin >> inName2;
    cout <<'\n';
    inFile2.open(inName2, ios::in);
    if (inFile2.fail())//if file cannot be opened, a message will display
        {
            cerr << "Could not open " << inName2 << "!" << endl;
            return EXIT_FAILURE;
        }    
        
    cout << "Please type the name of the output file, including the extension: ";//requests user input of filename
    cin >> outName;
    cout <<'\n';
    outFile.open(outName, ios::out);
    if (outFile.fail())//if file cannot be opened, a message will display
        {
            cerr << "Could not open " << outName << "!" << endl;
            return EXIT_FAILURE;
        }
   
    readWriteData(outFile, inFile1, inFile2);
    return 0;
    
}
void readWriteData(fstream& outFile, fstream& inFile1, fstream& inFile2)
{
     string in1;
     string in2;
  
	 do
      {
		  getline(inFile1, in1);
		  getline(inFile2, in2);
           
             if (strcmp(in1.c_str(), in2.c_str()) < 0)
             {
                outFile << in1 << '\n';
				outFile << in2 << '\n';  
			 }
              
            else if (strcmp(in1.c_str(), in2.c_str()) > 0)
			  {	
	             outFile << in2 << '\n';
                 outFile << in1 << '\n';  
			  }
			else if (strcmp(in1.c_str(), in2.c_str()) == 0)
			{
                outFile << in1 << '\n';
				outFile << in2 << '\n';  
			 }
		}
	  while (!inFile2.eof() || !inFile1.eof());
	  
	   inFile1.close();
       inFile2.close();
       outFile.close();
}

When I use this code, there are duplicate lines put to the output file. If I use this code:

#include <iostream>
#include <iomanip>
#include <cmath>
#include <cstdlib>     
#include <fstream>  
#include <cstring>  
#include <string>

using namespace std;

int openFile(fstream& f, fstream& f1, fstream& f2);//function to open the files
void readWriteData(fstream& f, fstream& f1, fstream& f2);//function to read and write data


int main()
{
    fstream outFile; //output
    fstream inFile1;//input
    fstream inFile2;//input
    
    openFile(outFile, inFile1, inFile2);
    cin.get();
    return 0;    
}


int openFile(fstream& outFile, fstream& inFile1, fstream& inFile2)
{
    char outName[50];//storage of user input filename for the data file that is to be written to
    char inName1[50];//storage of user input filename for the first data file that is to be read from
    char inName2[50];//storage of user input filename for the second data file that is to be read from
    
    cout << "Please type the name of the first input file, including the extension: ";//requests user input of filename
    cin >> inName1;
    cout <<'\n';
    inFile1.open(inName1, ios::in);   
    if (inFile1.fail())//if file cannot be opened, a message will display
        {
            cerr << "Could not open " << inName1 << "!" << endl;
            return EXIT_FAILURE;
        }
    
    cout << "Please type the name of the second input file, including the extension: ";//requests user input of filename
    cin >> inName2;
    cout <<'\n';
    inFile2.open(inName2, ios::in);
    if (inFile2.fail())//if file cannot be opened, a message will display
        {
            cerr << "Could not open " << inName2 << "!" << endl;
            return EXIT_FAILURE;
        }    
        
    cout << "Please type the name of the output file, including the extension: ";//requests user input of filename
    cin >> outName;
    cout <<'\n';
    outFile.open(outName, ios::out);
    if (outFile.fail())//if file cannot be opened, a message will display
        {
            cerr << "Could not open " << outName << "!" << endl;
            return EXIT_FAILURE;
        }
   
    readWriteData(outFile, inFile1, inFile2);
    return 0;
    
}
void readWriteData(fstream& outFile, fstream& inFile1, fstream& inFile2)
{
     string in1;
     string in2;
  
	 do
      {
		  getline(inFile1, in1);
		  getline(inFile2, in2);
           
             if (strcmp(in1.c_str(), in2.c_str()) < 0)
             {
                outFile << in1 << '\n';
				outFile << in2 << '\n';  
			 }
              
            else if (strcmp(in1.c_str(), in2.c_str()) > 0)
			  {	
	             outFile << in2 << '\n';
                 outFile << in1 << '\n';  
			  }
			else if (strcmp(in1.c_str(), in2.c_str()) == 0)
			{
                outFile << in1 << '\n';
				outFile << in2 << '\n';  
			 }
		}
	  while (!inFile2.eof() && !inFile1.eof());
	   

	  do
	  {
		  if (inFile1.eof())
			{
				getline(inFile2, in2);
				outFile << in2 << '\n';
			}
		  else if (inFile2.eof())
		  {
				getline(inFile1, in1);
				outFile << in1 << '\n';

		  }
		}
	  while (!inFile2.eof() || !inFile1.eof());
	   inFile1.close();
       inFile2.close();
       outFile.close();
}

There are no duplicates but then the remainder of the output is not alphabetical. Does anyone know of a better way I can achieve what I want to do?

[matsp]

C++ strings can be compared directly - and your comparisons are a bit overcomplicated - so simplified I'd do like this:

// Since equal strings can be in "either order" and still be correct, we just let the first case handle that.
             if (in1 <= in2)
             {
                outFile << in1 << '\n';
	        outFile << in2 << '\n';  
	    }
            else 
            {	
                  outFile << in2 << '\n';
                  outFile << in1 << '\n';  
            }

There is no need to get the C-string from a C++ string to compare the strings.

If you still insist on using c_str() to get the string, why not do:

// Since equal strings doesn't matter, just cover this case here, rather than 
// a separate case. 

          if (strcmp(in1.c_str(), in2.c_str()) <= 0)
          {
               outFile << in1 << '\n';
  	       outFile << in2 << '\n';  
          }
// As the only other alternative, we swap the strings. No need to compare the strings - they haven't changed.
          else 
          {	
	        outFile << in2 << '\n';
                outFile << in1 << '\n';  
	  }

This way, at least you are not comparing the same string up to 3 times (the compiler MAY realize that the strcmp() function always returns the same thing for the same input, but that's far from guaranteed).

I prefer the first code-sequence.

--
Mats