1. Input and Output 23: Input and Output
Programming C# © 2003 DevelopMentor, Inc.
12/1/2003

2. Objectives Survey IO facilities in .NET Framework Class Library
23: 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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3. IO Library Input/output library in System.IO namespace
23: Input and Output
IO Library
Input/output library in System.IO namespace
Support provided for:
file and directory management
text files
binary files
simple type conversion to/from binary
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4. 23: Input and Output
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
FileSystemInfo
DirectoryInfo
FileInfo
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5. FileSystemInfo Files and directories have some operations in common
23: Input and Output
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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6. DirectoryInfo DirectoryInfo represents a directory
23: Input and Output
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
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7. FileInfo FileInfo represents a file
23: Input and Output
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
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8. Application: List contents
23: Input and Output
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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9. Application: Find file
23: Input and Output
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
ArrayList results = new ArrayList();
Find("mscoree.dll", root, results);
foreach (string s in results)
Console.WriteLine(s);
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10. 23: Input and Output
Utility classes
Three utility classes also work with files and directories
Path
Directory
File
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11. Path Path provides static methods to manipulate a path string
23: Input and Output
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;
... }
Programming C# © 2003 DevelopMentor, Inc.
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12. Application: parse path
23: Input and Output
Application: parse path
Path methods useful to parse path into constituent parts
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
.dll
C:\
string path
Parse(path);
Programming C# © 2003 DevelopMentor, Inc.
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13. Directory Directory has static methods to manipulate directories
23: Input and Output
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
Programming C# © 2003 DevelopMentor, Inc.
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14. Application: examine drives
23: Input and Output
Application: examine drives
Can examine all logical drives
use Directory.GetLogicalDrives to get drives
use Directory.Exists to determine if disk in drive
all drives
string[] drives = Directory.GetLogicalDrives();
foreach (string s in drives) {
if (Directory.Exists(s))
... }
disk in drive?
Programming C# © 2003 DevelopMentor, Inc.
12/1/2003

15. File File has static methods to manipulate files
23: Input and Output
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
Programming C# © 2003 DevelopMentor, Inc.
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16. Choice of file / directory class
23: Input and Output
Choice of file / directory class
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
Programming C# © 2003 DevelopMentor, Inc.
12/1/2003

17. File contents manipulation
23: Input and Output
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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18. Character IO Classes provided to do character IO
23: Input and Output
Character IO
Classes provided to do character IO
most methods defined in base classes
derived classes specialized for data location and operation
TextReader
TextWriter
StreamWriter
StringWriter
StreamReader
StringReader
write to disk
write to StringBuilder
read from disk
read from string
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19. StreamWriter StreamWriter writes characters to text file
23: Input and Output
StreamWriter
StreamWriter writes characters to text file
open file with one of many constructors
write with overloaded Write / WriteLine methods
close
automatically
converted to string
using ToString
char, bool, string,
short, int, long,
float, double, etc.
text file
open
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();
write
close
Programming C# © 2003 DevelopMentor, Inc.
12/1/2003

20. StreamReader StreamReader reads characters from text file
23: Input and Output
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
open
StreamReader sr = new StreamReader("Chores.txt");
string s;
while ((s = sr.ReadLine()) != null)
Console.WriteLine(s);
sr.Close();
read
close
Programming C# © 2003 DevelopMentor, Inc.
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21. Byte IO Classes provided to do byte IO
23: Input and Output
Byte IO
Classes provided to do byte IO
most methods defined in base class
Two possible data locations provided in System.IO
disk
memory
Stream
FileStream
MemoryStream
read/write disk
read/write byte array
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22. Stream methods Stream offers extensive functionality
23: Input and Output
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
Programming C# © 2003 DevelopMentor, Inc.
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23. FileStream FileStream supports read / write bytes to disk file open
23: Input and Output
FileStream
FileStream supports read / write bytes to disk file
open
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();
byte,
byte[]
binary file
write
back up 2 bytes
back up to beginning
close
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24. Simple type output BinaryWriter converts many core types to binary
23: Input and Output
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
char, bool, string,
short, int, long,
float, double, etc.
simple types
converter
bytes
binary file
data store
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();
converter
write
close both
streams
Programming C# © 2003 DevelopMentor, Inc.
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25. Simple type input BinaryReader reconstructs types from binary
23: Input and Output
Simple type input
BinaryReader reconstructs types from binary
must be given a stream containing bytes
Read methods read from backing stream and convert
char, bool, string,
short, int, long,
float, double, etc.
simple types
converter
bytes
binary file
data store
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();
converter
read
close both
streams
Programming C# © 2003 DevelopMentor, Inc.
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26. Serialization Can save/restore state of object to stream
23: Input and Output
Serialization
Can save/restore state of object to stream
called serialization
save
x 1
y 2
serialize
Point x=1, y=2 ...
restore
deserialize
x 1
y 2
Point x=1, y=2 ...
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27. Serializable attribute
23: Input and Output
Serializable attribute
Type author must explicitly allow serialization
tag with Serializable attribute to allow
otherwise get SerializationException
allow points to
be serialized
[Serializable]
class Point {
int x;
int y;
... }
Programming C# © 2003 DevelopMentor, Inc.
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28. Formatter BinaryFormatter used to serialize/deserialize object
23: Input and Output
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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29. Save Use Serialize method to save object to stream void Write() {
23: Input and Output
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);
... }
Programming C# © 2003 DevelopMentor, Inc.
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30. Restore Use Deserialize method to restore object from stream
23: Input and Output
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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31. Object graph Serialization preserves object graph
23: Input and Output
Object graph
Serialization preserves object graph
all referenced objects are serialized
graph rebuilt when deserialized
x 1
y 2
center
radius 3 c
Both circle and center
point would be serialized
Programming C# © 2003 DevelopMentor, Inc.
12/1/2003

32. Summary IO facilities provided by .NET Framework class library
23: Input and Output
Summary
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
Programming C# © 2003 DevelopMentor, Inc.
12/1/2003