.net - Writing huge amount of physical file names into text files c# -

i have developed small tool used display data discrepancy in c#, explained point wise below,

1. fetch data database , write list of file names in text file based on date criteria -output 1
2. take dir of path 1 , write text file- output2
3. take dir of path2, path3 , path4 , write text files separately each path- output 3/4/5
4. compare option: compare output1 , 2 , write down difference in text file, difference compared output3 , again difference written in file, , on...
5. my issue : last path has more 2.5 million records of files, whenever try writing in text file hangs application , never provides output, did try filtering date criteria single day records around 30 thousands hangs

i have searched many sites did not solution can understand or able implement it. below attempted code.

if (!txtpath3.text.equals(string.empty) && system.io.directory.getfiles(txtpath3.text).length > 0) {     var directory = txtpath3.text;     var from_dt = this.dtpickerstart.value;     var end_dt = this.dtpickerend.value;      datetime from_date = from_dt;     datetime to_date = end_dt;      directoryinfo di = new directoryinfo(directory);     filesysteminfo[] files = di.getfilesysteminfos();      var op = di.getfiles()         .where(file => file.lastwritetime >= from_date && file.lastwritetime <= to_date);      foreach (string file in system.io.directory.getfiles(txtpath3.text, "*.*"))     {         textwriter tw = new streamwriter(dirfile3, true);         tw.writeline("" + file + "");         tw.close();     } } else {  } 

your foreach-loop opens , closes file lines. should open , close file outside of loop.

using(var tw = new streamwriter(dirfile3, true)) {     foreach (string file in system.io.directory.getfiles(txtpath3.text, "*.*"))     {         tw.writeline("" + file + "");     } } 

even easier using existing functions this:

file.appendalllines(dirfile3, system.io.directory.getfiles(txtpath3.text, "*.*")); 

as 2.5 million filesnames lot keep in ram @ same time, might better off enumerating them:

file.appendalllines(dirfile3, system.io.directory.enumeratefiles(txtpath3.text, "*.*"));