Chapter97:FileandStreamI/O

Parameter                                                                Details

path                The locationof thefile.

append           Ifthefileexist,truewilladddatatotheendofthefile(append),falsewilloverwritethefile. text Text to be written or stored.

contents        A collection of strings to be written.

source            The location of the file you want to use.

dest       The location you want a file to go to.

Managesfiles.

Section97.1:ReadingfromafileusingtheSystem.IO.Fileclass

YoucanusetheSystem.IO.File.ReadAllTextfunctiontoreadtheentirecontentsofafileintoastring.

stringtext=System.IO.File.ReadAllText(@”C:\MyFolder\MyTextFile.txt”);

YoucanalsoreadafileasanarrayoflinesusingtheSystem.IO.File.ReadAllLinesfunction:

string[]lines=System.IO.File.ReadAllLines(@”C:\MyFolder\MyTextFile.txt”);

Section97.2:Lazilyreadingafileline-by-lineviaan IEnumerable

When working with large files, you can use the System.IO.File.ReadLinesmethod to read all lines from a file into anIEnumerable<string>.ThisissimilartoSystem.IO.File.ReadAllLines,exceptthatitdoesn’tloadthewholefile intomemoryatonce,makingitmoreefficientwhenworkingwithlargefiles.

IEnumerable<string>AllLines=File.ReadLines(“file_name.txt”,Encoding.Default);

ThesecondparameterofFile.ReadLinesisoptional.Youmayuseitwhenitisrequiredtospecifyencoding.

ItisimportanttonotethatcallingToArray,ToListoranothersimilarfunctionwillforceallofthelinestobeloaded atonce,meaningthatthebenefitofusingReadLinesisnullified.ItisbesttoenumerateovertheIEnumerableusing a foreachloop or LINQ if using this method.

Section 97.3: Asyncwrite textto afile usingStreamWriter

//filenameisastringwiththefullpath

//trueistoappend

using(System.IO.StreamWriterfile=newSystem.IO.StreamWriter(filename,true))

{

//Canwriteeitherastringorchararray

awaitfile.WriteAsync(text);

}

Section97.4:CopyFile

Filestaticclass

Filestaticclasscanbeeasilyusedforthispurpose.

File.Copy(@”sourcePath\abc.txt”,@”destinationPath\abc.txt”); File.Copy(@”sourcePath\abc.txt”,@”destinationPath\xyz.txt”);

Remark:Bythismethod,fileiscopied,meaningthatitwillbereadfromthesourceandthenwrittentothe destinationpath.Thisisaresourceconsumingprocess,itwouldtakerelativetimetothefilesize,andcancause your program to freeze if you don’t utilize threads.

Section97.5:Writinglinestoafileusingthe System.IO.StreamWriterclass

TheSystem.IO.StreamWriterclass:

ImplementsaTextWriterforwritingcharacterstoastreaminaparticularencoding.

UsingtheWriteLinemethod,youcanwritecontentline-by-linetoafile.

Notice the use of the usingkeyword which makes sure the StreamWriter object is disposed as soon as it goes out of scope and thus the file is closed.

string[]lines={“Myfirststring”,”Mysecondstring”,”andevenathirdstring”};

using(System.IO.StreamWritersw=newSystem.IO.StreamWriter(@”C:\MyFolder\OutputText.txt”))

{

foreach(stringlineinlines)

{

sw.WriteLine(line);

}

}

Note that the StreamWriter can receive a second boolparameter in it’s constructor, allowing to Appendto a file instead of overwriting the file:

boolappendExistingFile=true;

using(System.IO.StreamWritersw=newSystem.IO.StreamWriter(@”C:\MyFolder\OutputText.txt”, appendExistingFile))

{

sw.WriteLine(“Thislinewillbeappendedtotheexistingfile”);

}

Section97.6:WritingtoafileusingtheSystem.IO.Fileclass

YoucanusetheSystem.IO.File.WriteAllTextfunctiontowriteastringtoafile.

stringtext=”Stringthatwillbestoredinthefile”;

System.IO.File.WriteAllText(@”C:\MyFolder\OutputFile.txt”,text);

You can also use the System.IO.File.WriteAllLinesfunction which receives an IEnumerable<String>as the second parameter(asopposedtoasinglestringinthepreviousexample).Thisletsyouwritecontentfromanarrayoflines.

string[]lines={“Myfirststring”,”Mysecondstring”,”andevenathirdstring”}; System.IO.File.WriteAllLines(@”C:\MyFolder\OutputFile.txt”,lines);

Section97.7:CreateFile

Filestaticclass

ByusingCreatemethodoftheFilestaticclasswecancreatefiles.Methodcreatesthefileatthegivenpath,atthe sametimeitopensthefileandgivesustheFileStreamofthefile.Makesureyouclosethefileafteryouaredone with it.

ex1:

varfileStream1=File.Create(“samplePath”);

///youcanwritetothefileStream1

fileStream1.Close();

ex2:

using(varfileStream1=File.Create(“samplePath”))

{

///youcanwritetothefileStream1

}

ex3:

File.Create(“samplePath”).Close();

FileStreamclass

Therearemanyoverloadsofthisclassesconstructorwhichisactuallywelldocumentedhere.Belowexampleisfor the one that covers most used functionalities of this class.

varfileStream2=newFileStream(“samplePath”,FileMode.OpenOrCreate,FileAccess.ReadWrite,FileShare.None);

You can check the enums for FileMode, FileAccess, and FileSharefrom those links. What they basically means are asfollows:

FileMode:Answers”Shouldfilebecreated?opened?createifnotexistthenopen?”kindaquestions.

FileAccess:Answers”ShouldIbeabletoreadthefile,writetothefileorboth?”kindaquestions.

FileShare:Answers”Shouldotherusersbeabletoread,writeetc.tothefilewhileIamusingitsimultaneously?” kinda questions.

Section97.8:MoveFile

Filestaticclass

Filestaticclasscaneasilybeusedforthispurpose.

File.Move(@”sourcePath\abc.txt”,@”destinationPath\xyz.txt”);

Remark1: Onlychangestheindexofthefile(ifthefileismovedinthesamevolume).Thisoperationdoesnottake relative time to the file size.

Remark2:Cannotoverrideanexistingfileondestinationpath.

Section97.9:DeleteFile

stringpath=@”c:\path\to\file.txt”;

File.Delete(path);

While Deletedoes not throw exception if file doesn’t exist, it will throw exception e.g. if specified path is invalid or caller does not have the required permissions. You should always wrap calls to Deleteinside try-catch block and handle all expected exceptions. In case of possible race conditions, wrap logic inside lock statement.

Section97.10:FilesandDirectories

GetallfilesinDirectory

varFileSearchRes=Directory.GetFiles(@Path,”*.*”,SearchOption.AllDirectories);

ReturnsanarrayofFileInfo,representingallthefilesinthespecifieddirectory.

GetFileswithspecificextension

varFileSearchRes=Directory.GetFiles(@Path,”*.pdf”,SearchOption.AllDirectories);

ReturnsanarrayofFileInfo,representingallthefilesinthespecifieddirectorywiththespecifiedextension.