C# 0 The Complete Reference

ArgumentNullException

 is thrown. If 

outputStream

 has not been opened for writing, 

ArgumentException

 is thrown.

BinaryWriter

 defines methods that can write all of C#’s built-in types. Several are 

shown in Table 14-5. Notice that a 

string

 is written using its internal format, which includes 

a length specifier. 

BinaryWriter

 also defines the standard 

Close( )

 and 

Flush( )

 methods, 

which work as described earlier.

BinaryReader

A

BinaryReader

 is a wrapper around a byte stream that handles the reading of binary data. 

Its most commonly used constructor is shown here:

BinaryReader(Stream 

inputStream

)

Here, 

inputStream

 is the stream from which data is read. To read from a file, you can use 

the object created by 

FileStream

 for this parameter. If 

inputStream

 has not been opened for 

reading or is otherwise invalid, 

ArgumentException

 is thrown.

BinaryReader

 provides methods for reading all of C#’s simple types. Several commonly 

used methods are shown in Table 14-6. Notice that 

ReadString( )

 reads a 

string

 that is stored 

using its internal format, which includes a length specifier. These methods throw an 

IOException

 if an error occurs. (Other exceptions are also possible.)

Method

Description

void Write(sbyte 

val

)

Writes a signed byte.

void Write(byte 

val

)

Writes an unsigned byte.

void Write(byte[ ] 

buf

)

Writes an array of bytes.

void Write(shor t 

val

)

Writes a shor t integer.

void Write(ushor t 

val

)

Writes an unsigned shor t integer.

void Write(int 

val

)

Writes an integer.

void Write(uint 

val

)

Writes an unsigned integer.

void Write(long 

val

)

Writes a long integer.

void Write(ulong 

val

)

Writes an unsigned long integer.

void Write(float 

val

)

Writes a 

float

.

void Write(double 

val

)

Writes a 

double

.

void Write(char 

val

)

Writes a character.

void Write(char[ ] 

buf

)

Writes an array of characters.

void Write(string 

val

)

Writes a 

string

 using its internal representation, which includes a 

length specifier.

T

ABLE

 14-5 

Commonly Used Output Methods Defi ned by 

BinaryWriter

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BinaryReader

 also defines three versions of 

Read( )

, which are shown here:

Method

Description

int Read( )

Returns an integer representation of the next 

available character from the invoking input stream. 

Returns –1 when attempting to read at the end of 

the file.

int Read(byte[ ] 

buf

, int 

offset

, int 

num

)

Attempts to read up to 

num

 bytes into 

buf

 star ting 

at

buf

[

offset

], returning the number of bytes 

successfully read. 

int Read(char[ ] 

buf

, int 

offset

, int 

num

)

Attempts to read up to 

num

 characters into 

buf

star ting at 

buf

[

offset

], returning the number of 

characters successfully read. 

These methods will throw an 

IOException

 on failure. Other exceptions are possible. Also 

defined is the standard 

Close( )

 method.

Method

Description

bool ReadBoolean( )

Reads a 

bool

.

byte ReadByte( )

Reads a 

byte

.

sbyte ReadSByte( )

Reads an 

sbyte

.

byte[ ] ReadBytes(int 

num

)

Reads 

num

 bytes and returns them as an array.

char ReadChar( )

Reads a 

char

.

char[ ] ReadChars(int 

num

)

Reads 

num

 characters and returns them as an array.

double ReadDouble( )

Reads a 

double

.

float ReadSingle( )

Reads a 

float

.

shor t ReadInt16( )

Reads a 

short

.

int ReadInt32( )

Reads an 

int

.

long ReadInt64( )

Reads a 

long

.

ushor t ReadUInt16( )

Reads a 

ushort

.

uint ReadUInt32( )

Reads a 

uint

.

ulong ReadUInt64( )

Reads a 

ulong

.

string ReadString( )

Reads a 

string

 that is represented in its internal, binar y 

format, which includes a length specifier. This method 

should only be used to read a string that has been written 

using a 

BinaryWriter

.

T

ABLE

 14-6 

Commonly Used Input Methods Defi ned by 

BinaryReader

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Demonstrating Binary I/O

Here is a program that demonstrates 

BinaryReader

 and 

BinaryWriter

. It writes and then 

reads back various types of data to and from a file.

// Write and then read back binary data.

using System;

using System.IO;

class RWData {

  static void Main() {

    BinaryWriter dataOut;

    BinaryReader dataIn;

    int i = 10;

    double d = 1023.56;

    bool b = true;

    string str = "This is a test";

    try {

      dataOut = new

        BinaryWriter(new FileStream("testdata", FileMode.Create));

    }

    catch(IOException exc) {

      Console.WriteLine("Cannot Open File For Output");

      Console.WriteLine(exc.Message);

      return;

    }

    // Write data to a file.

    try {

      Console.WriteLine("Writing " + i);

      dataOut.Write(i);

      Console.WriteLine("Writing " + d);

      dataOut.Write(d);

      Console.WriteLine("Writing " + b);

      dataOut.Write(b);

      Console.WriteLine("Writing " + 12.2 * 7.4);

      dataOut.Write(12.2 * 7.4);

      Console.WriteLine("Writing " + str);

      dataOut.Write(str);

    }

    catch(IOException exc) {

      Console.WriteLine("Error Writing File");

      Console.WriteLine(exc.Message);

    }

    dataOut.Close();

    Console.WriteLine();

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    // Now, read the data.

    try {

      dataIn = new

          BinaryReader(new FileStream("testdata", FileMode.Open));

    }

    catch(IOException exc) {

      Console.WriteLine("Cannot Open File For Input");

      Console.WriteLine(exc.Message);

      return;

    }

    try {

      i = dataIn.ReadInt32();

      Console.WriteLine("Reading " + i);

      d = dataIn.ReadDouble();

      Console.WriteLine("Reading " + d);

      b = dataIn.ReadBoolean();

      Console.WriteLine("Reading " + b);

      d = dataIn.ReadDouble();

      Console.WriteLine("Reading " + d);

      str = dataIn.ReadString();

      Console.WriteLine("Reading " + str);

    }

    catch(IOException exc) {

      Console.WriteLine("Error Reading File");

      Console.WriteLine(exc.Message);

    }

    dataIn.Close();

  }

}

The output from the program is shown here:

Writing 10

Writing 1023.56

Writing True

Writing 90.28

Writing This is a test

Reading 10

Reading 1023.56

Reading True

Reading 90.28

Reading This is a test

If you examine the 

testdata

 file produced by this program, you will find that it contains 

binary data, not human-readable text.

Here is a more practical example that shows how powerful binary I/O is. The following 

program implements a very simple inventory program. For each item in the inventory, the 

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program stores the item’s name, the number on hand, and its cost. Next, the program prompts 

the user for the name of an item. It then searches the database. If the item is found, the 

inventory information is displayed.

/* Use BinaryReader and BinaryWriter to implement

   a simple inventory program. */

using System;

using System.IO;

class Inventory {

  static void Main() {

    BinaryWriter dataOut;

    BinaryReader dataIn;

    string item; // name of item

    int onhand;  // number on hand

    double cost; // cost

    try {

      dataOut = new

        BinaryWriter(new FileStream("inventory.dat",

                                    FileMode.Create));

    }

    catch(IOException exc) {

      Console.WriteLine("Cannot Open Inventory File For Output");

      Console.WriteLine(exc.Message);

      return;

    }

    // Write some inventory data to the file.

    try {

      dataOut.Write("Hammers");

      dataOut.Write(10);

      dataOut.Write(3.95);

      dataOut.Write("Screwdrivers");

      dataOut.Write(18);

      dataOut.Write(1.50);

      dataOut.Write("Pliers");

      dataOut.Write(5);

      dataOut.Write(4.95);

      dataOut.Write("Saws");

      dataOut.Write(8);

      dataOut.Write(8.95);

    }

    catch(IOException exc) {

      Console.WriteLine("Error Writing Inventory File");

      Console.WriteLine(exc.Message);

    }

    dataOut.Close();

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