Input and Output Objectives Survey IO facilities in .NET - - PDF document

Input and Output

Objectives

• Survey IO facilities in .NET Framework Class Library

– file and directory management – text files – binary files – object serialization

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IO Library

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• Input/output library in System.IO namespace
• Support provided for:

– file and directory management – text files – binary files – simple type conversion to/from binary

Files and directories

• Two primary classes to work with files and directories

– perform file system interaction – generally do not manipulate file contents – derived from common base

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FileSystemInfo DirectoryInfo FileInfo

FileSystemInfo

• Files and directories have some operations in common

– provided in base class FileSystemInfo

public abstract class FileSystemInfo ... { public abstract string Name { get; } public string FullName { get; } public string Extension { get; } public abstract bool Exists { get; } public DateTime CreationTime { get; set; } public DateTime LastAccessTime { get; set; } public DateTime LastWriteTime { get; set; } public FileAttributes Attributes { get; set; } public void Delete() ... ... }

name characteristics delete

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DirectoryInfo

• DirectoryInfo represents a directory

– methods provided to examine and manipulate – inherits common operations from FileSystemInfo

public sealed class DirectoryInfo : FileSystemInfo { public DirectoryInfo(string path) ... public DirectoryInfo Parent { get; } public DirectoryInfo Root { get; } public void Create () ... public void MoveTo (string destDirName) ... public void Delete (bool recursive ) ... public DirectoryInfo CreateSubdirectory(string path ) ... public FileInfo [] GetFiles () ... public DirectoryInfo [] GetDirectories () ... public FileSystemInfo[] GetFileSystemInfos() ... ... } constructor navigation manipulation contents 6

FileInfo

• FileInfo represents a file

– methods provided to examine and manipulate – inherits common operations from FileSystemInfo

public sealed class FileInfo : FileSystemInfo { public FileInfo(string fileName) ... public long Length { get; } public string DirectoryName { get; } public DirectoryInfo Directory { get; } public FileInfo CopyTo(string destFileName) ... public FileInfo CopyTo(string destFileName, bool overwrite) ... public void MoveTo(string destFileName) ... ... } constructor length location manipulation 7

Application: List contents

• Can examine contents of a directory

void List(string path) { DirectoryInfo directory = new DirectoryInfo(path); FileInfo [] files = directory.GetFiles (); DirectoryInfo[] directories = directory.GetDirectories(); foreach (FileInfo f in files) Console.WriteLine(f.Name); foreach (DirectoryInfo d in directories) Console.WriteLine(d.Name); } contents files directories

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Application: Find file

• Can search file system to find specified files

void Find(string filename, DirectoryInfo root, ArrayList results) { foreach (FileInfo f in root.GetFiles(filename)) results.Add(f.FullName); foreach (DirectoryInfo d in root.GetDirectories()) Find(filename, d, results); } search with pattern recursive call for each subdirectory DirectoryInfo root = new DirectoryInfo(@"C:\WINDOWS"); ArrayList results = new ArrayList(); Find("mscoree.dll", root, results); foreach (string s in results) Console.WriteLine(s); 9

Utility classes

• Three utility classes also work with files and directories

– Path – Directory – File

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Path

• Path provides static methods to manipulate a path string

– most do not interact with the file system

public sealed class Path { public static bool HasExtension (string path) ... public static string GetExtension (string path) ... public static string ChangeExtension(string path, string extension) ... public static string GetDirectoryName(string path) ... public static string GetFileName (string path) ... public static string GetFileNameWithoutExtension(string path) ... public static readonly char DirectorySeparatorChar; public static readonly char VolumeSeparatorChar; public static readonly char PathSeparator; ... } 11

Application: parse path

• Path methods useful to parse path into constituent parts

12 public void Parse(string path) { string a = Path.GetDirectoryName (path); string b = Path.GetFileName (path); string c = Path.GetFileNameWithoutExtension(path); string d = Path.GetExtension (path); string e = Path.GetPathRoot (path); ... } C:\WINDOWS\system32 mscoree.dll mscoree C:\ .dll string path = @"C:\WINDOWS\system32\mscoree.dll"; Parse(path);

Directory

• Directory has static methods to manipulate directories

– most have analogues in DirectoryInfo – several offer unique functionality

public sealed class Directory { public static string[] GetLogicalDrives() public static string GetCurrentDirectory() public static void SetCurrentDirectory(string path) public static bool Exists (string path) ... public static string[] GetFiles (string path) ... public static string[] GetDirectories(string path) ... public static void Delete (string path) public static void Move(string source, string dest) ... } all drives on system current directory similar methods in DirectoryInfo 13

Application: examine drives

• Can examine all logical drives

– use Directory.GetLogicalDrives to get drives – use Directory.Exists to determine if disk in drive

string[] drives = Directory.GetLogicalDrives(); foreach (string s in drives) { if (Directory.Exists(s)) ... }

all drives disk in drive?

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File

• File has static methods to manipulate files

– all have analogues in FileInfo

public sealed class File { public static bool Exists(string path) ... public static void Delete(string path) ... public static void Copy (string source, string dest) ... public static void Move (string source, string dest) ... ... } similar methods in FileInfo 15

Choice of file / directory class

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• Must sometimes decide which class to use

– File vs. FileInfo – Directory vs. DirectoryInfo

• Static methods

– can offer more convenient usage syntax – require permission check on each call

• Instance methods

– must instantiate object – some permission checks can be done once in constructor

File contents manipulation

• Classes provided to manipulate file contents

– separate classes for text and binary files – filters convert simple types to/from bytes for binary storage – support for disk or memory files

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Character IO

• Classes provided to do character IO

– most methods defined in base classes – derived classes specialized for data location and operation

TextReader StreamReader StringReader TextWriter StreamWriter StringWriter

read from disk read from string write to disk write to StringBuilder

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StreamWriter

automatically converted to string using ToString

• StreamWriter writes characters to text file

– open file with one of many constructors – write with overloaded Write / WriteLine methods – close

char, bool, string, short, int, long, float, double, etc.

text file StreamWriter sw = new StreamWriter("Chores.txt"); int n = 3; sw.WriteLine("Go to pet store"); sw.Write("Feed all "); sw.Write(n); sw.WriteLine(" cats"); sw.Close();

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write close

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StreamReader

• StreamReader reads characters from text file

– open file with one of many constructors – read characters or strings with Read / ReadLine methods – close

can read only char or string char, string

text file

StreamReader sr = new StreamReader("Chores.txt"); string s; while ((s = sr.ReadLine()) != null) Console.WriteLine(s); sr.Close();

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read close

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Byte IO

• Classes provided to do byte IO

– most methods defined in base class

• Two possible data locations provided in System.IO

– disk – memory

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Stream FileStream MemoryStream

read/write byte array read/write disk

Stream methods

• Stream offers extensive functionality

– read / write bytes – random access – asynchronous read / write

public abstract class Stream ... { public virtual int ReadByte () ... public virtual void WriteByte(byte value) ... public abstract int Read (byte[] buffer, int offset, int count); public abstract void Write(byte[] buffer, int offset, int count); public abstract long Seek (long offset, SeekOrigin origin); public abstract long Position { get; set; } public virtual IAsyncResult BeginRead (...) ... public virtual int EndRead (...) ... public virtual IAsyncResult BeginWrite(...) ... public virtual void EndWrite (...) ... ... } read/write random access asynch 22

FileStream

• FileStream supports read / write bytes to disk file

23 FileStream f = new FileStream ( "Bytes.dat", FileMode.Create, FileAccess.ReadWrite ); f.WriteByte((byte)10); f.WriteByte((byte)20); f.WriteByte((byte)30); f.WriteByte((byte)90); f.WriteByte((byte)50); f.Seek(-2, SeekOrigin.Current); f.WriteByte((byte)40); f.Seek(0, SeekOrigin.Begin); int b = f.ReadByte(); f.Close();

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write back up 2 bytes back up to beginning close

byte, byte[]

binary file

Simple type output

• BinaryWriter converts many core types to binary

– must be used with a stream for storage – Write methods convert and write bytes to backing stream

simple types bytes char, bool, string, short, int, long, float, double, etc.

converter binary file

FileStream data = new FileStream("Bytes.dat", FileMode.Create); BinaryWriter converter = new BinaryWriter(data); converter.Write(17); converter.Write(3.14); converter.Write("hello"); converter.Close(); data store converter write close both streams 24

Simple type input

• BinaryReader reconstructs types from binary

– must be given a stream containing bytes – Read methods read from backing stream and convert

simple types bytes char, bool, string, short, int, long, float, double, etc.

converter binary file

FileStream data = new FileStream("Bytes.dat", FileMode.Open); BinaryReader converter = new BinaryReader(data); int i = converter.ReadInt32 (); double d = converter.ReadDouble(); string s = converter.ReadString(); converter.Close(); data store converter read close both streams 25

Serialization

• Can save/restore state of object to stream

– called serialization

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x 1 y 2

serialize

save

Point x=1, y=2 ... x 1 y 2

deserialize

restore

Point x=1, y=2 ...

Serializable attribute

• Type author must explicitly allow serialization

– tag with Serializable attribute to allow – otherwise get SerializationException

[Serializable] class Point { int x; int y; ... }

allow points to be serialized

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Formatter

• BinaryFormatter used to serialize/deserialize object

– in namespace System.Runtime.Serialization.Formatters.Binary

public sealed class BinaryFormatter ... { public void Serialize(Stream destination, object o) { ... } public object Deserialize(Stream source) { ... } ... } save object to stream restore object from stream

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Save

• Use Serialize method to save object to stream

void Write() { FileStream dest = new FileStream("MyData.dat", FileMode.Create); Point data = new Point(1, 2); BinaryFormatter formatter = new BinaryFormatter(); formatter.Serialize(dest, data); ... }

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Restore

• Use Deserialize method to restore object from stream

– return type is object, typical to downcast

void Read() { FileStream source = new FileStream("MyData.dat", FileMode.Open); BinaryFormatter formatter = new BinaryFormatter(); Point data = (Point)formatter.Deserialize(source); ... }

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Object graph

• Serialization preserves object graph

– all referenced objects are serialized – graph rebuilt when deserialized

center radius 3 c x 1 y 2

Both circle and center point would be serialized

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Summary

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• IO facilities provided by .NET Framework class library

– in System.IO namespace

• Can manipulate files and directories
• Can read/write file contents

– characters – bytes

• Can convert simple types to/from binary format
• Serialization allows objects to be read/written to stream