Comparing two text files...........


  I have two text files. Each file contains huge data, say 1000 to 2000 lines. Now i want to compare these two files and produce the differences.
  Since the file size is big, i dont want to perform character by character comparision. One point that we have to consider is, each line in the file doesnt exceed 512 characters. This helps us to comapare line by line comaprision.

  I was wondering if anybody has an idea of how i could do this.

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Why reinventing the wheel? Check out the GNU 'diff' code:
Or have a look at to get the sources for winmerge.
I'd use jkr's solution.

However, comparing differences line per line is easy to write :

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

using namespace std;

int main()
    ifstream file1("foo.dat", ios::binary);
    ifstream file2("bar.dat", ios::binary);

    if(!file1 || !file2)
        return 1;

    int line=0;
    string s1,s2;
    while(getline(file1,s1) && getline(file2,s2))
            cout << "Difference at line " << line << " :" << endl;
            cout << "File1 : " << s1 << endl;
            cout << "File2 : " << s2 << endl;
            cout << "-----------------" << endl;

    // TODO : handle different sizes of files

    return 0;

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>> and produce the differences.

What do you mean by this?

You could always say something like,

ifstream in1( "myfile1.txt", ios::in ), in2( "myfile2.txt", ios::in );
string line1, line2, relationship;
unsigned int counter = 0;
int result;

while( in1 && in2 )
    in1 >> line1;
    in2 >> line2;
    result = line2 );

    if( result == 0 )
        relationship = "equal to";
    if( result < 0 )
        relationship = "less than";
    if( result > 0 )
        relationship = "greater than";

    cout << "Line " << counter << " in file 1 is " << relationship << " line " << counter << " in file 2."  << endl;



It would be helpfull if you clarified what you meant by the "differences" between the files.

Note: I did not compile this.

EarthQuaker, it seams we posted similar code. You posted while I was still typing. :-)
Exceter, no worries.

But I'll maybe just notice that your code processes the file word per word without comparing spaces, newlines char and others skipped chars by operator>>()

Nothing really bad, but as you said the user should refine what he means by "difference".
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