c# 4.0 - extracting lines from a file with C# -

i have text file1 , wish extract lines (which don't exist in file2)in new file3

example :

file1:

/** * gets total volume. * * @return total volume */ public int gettotalvolume() {return totalvolume;} 

file2:

* gets total volume. * * @return total volume 

file3:

/**  */ public int gettotalvolume() {return totalvolume;} 

my function:

    public void traitv2(string file1, string file2, string file3)     {         streamreader monstreamreaderfile1 = new streamreader(file1);         streamwriter monstreamwriterfile3 = new streamwriter(file3);         string ligne = monstreamreaderfile1.readline();          while (ligne != null)         {             streamreader monstreamreaderfile2 = new streamreader(file2);             string ligne1 = monstreamreaderfile2.readline();             while (ligne1 != null)             {                 if (!ligne.equals(ligne1))                 {                      console.writeline(ligne);                     monstreamwriterfile3.writeline(ligne);                 }                  ligne1 = monstreamreaderfile2.readline();                 ligne = monstreamreaderfile1.readline();             }              ligne = monstreamreaderfile1.readline();             monstreamreaderfile2.close();         }          monstreamwriterfile3.close();         monstreamreaderfile1.close();     } 

when run function, result false , error occurs: error object reference not set instance of object

simple solution using linq:

var file1 = file.readalllines("file1name"); var file2 = file.readalllines("file2name"); var file3 = file1.except(file2); file.writealllines("filename3", file3);