Compare two text files line by line

Question

Beneath here i described a example Scenario:

"FileA-Database.txt" contains the following names:

KB200

KB300

KB400

"FileB-Slave.txt" contains the following names:

KB600

KB200

KB400

KB700

I want to compare the "FileA-Database.txt" with "FileB-Slave.txt" and let the missing values be filled in automatically in the "FileA-Database.txt" file also i need to display the missing values in a text file called "Results.txt".

The code needs to be compatible with C# (framework 4.0+) please!.

I need a simple approach, mine doesnt work exactly the way i want it to:

    private void button_compare_Click(object sender, EventArgs e)
        {
            string fileA, fileB, fileC;
            fileA = "database-critical.txt";
            fileB = "patchlist.txt";
            fileC = "result.txt";

            string alphaFilePath = fileA;

            List<string> alphaFileContent = new List<string>();

            using (FileStream fs = new FileStream(alphaFilePath, FileMode.Open))
            using(StreamReader rdr = new StreamReader(fs))
            {
                while(!rdr.EndOfStream)
                {
                    alphaFileContent.Add(rdr.ReadLine());
                }
            }

            string betaFilePath = fileB;

            StringBuilder sb = new StringBuilder();


            using (FileStream fs = new FileStream(betaFilePath, FileMode.Open))
            using (StreamReader rdr = new StreamReader(fs))
            {
                while(! rdr.EndOfStream)
                {
                    string[] betaFileLine = rdr.ReadLine().Split(Convert.ToChar(","));

                    if (alphaFileContent.Contains(betaFileLine[0]))
                    {
                        sb.AppendLine(String.Format("{0}", betaFileLine[0]));
                    }
                }
            }

using (FileStream fs = new FileStream(fileC, FileMode.Create))
        using (StreamWriter writer = new StreamWriter(fs))
        {
            writer.Write(sb.ToString());
        }
    }

            //End
        }

Solution 1

String directory = @"C:\Whatever\";
String[] linesA = File.ReadAllLines(Path.Combine(directory, "FileA-Database.txt"));
String[] linesB = File.ReadAllLines(Path.Combine(directory, "FileB-Database.txt"));

IEnumerable<String> onlyB = linesB.Except(linesA);

File.WriteAllLines(Path.Combine(directory, "Result.txt"), onlyB);

Solution 2

Since your question seems like you made no effort whatsoever I'll give you just a rough outline.

1. Read both files line by line, e.g. with File.ReadAllLines or File.ReadLines.
2. Use LINQ's Except method.
3. Write the results into a new file.

Comments

[Developman]

I am trying, i need a simple approach... Posted what i have done :p

[Sergey Kulgan]

It is not standard comparison due files will be considered the same if the same set of lines has different sequence.

[Angelo]

i know this is an old question, but how will you deal with large files for example 1 gig or more? i tried this answer and ended up out of memory exception..

[null]

@Angelo did you ever find anything?

[Tommaso Belluzzo]

You could try the following: Enumerable<String> onlyB = linesB.AsParallel().Except(linesA.AsParallel());