pointer, structure ,union and intro to file handling

Unit-5.2
Pointer, Structure, Union
&
Intro to File Handling
Course: BTECH
Subject: Programming In C Language

What is a File?
• A file is a collection on information, usually
stored on a computer’s disk. Information can
be saved to files and then later reused.

File Names
• All files are assigned a name that is used for
identification purposes by the operating
system and the user.

Table
File Name and Extension File Contents
MYPROG.BAS BASIC program
MENU.BAT DOS Batch File
INSTALL.DOC Documentation File
CRUNCH.EXE Executable File
BOB.HTML HTML (Hypertext Markup Language) File
3DMODEL.JAVA Java program or applet
INVENT.OBJ Object File
PROG1.PRJ Borland C++ Project File
ANSI.SYS System Device Driver
README.TXT Text File

Focus on Software Engineering: The
Process of Using a File
• Using a file in a program is a simple three-step
process
– The file must be opened. If the file does not yet
exits, opening it means creating it.
– Information is then saved to the file, read from
the file, or both.
– When the program is finished using the file, the
file must be closed.

Setting Up a Program for File
Input/Output
• Before file I/O can be performed, a C++
program must be set up properly.
• File access requires the inclusion of fstream.h

Opening a File
• Before data can be written to or read from a
file, the file must be opened.
ifstream inputFile;
inputFile.open(“customer.dat”);

Program
// This program demonstrates the declaration of an fstream
// object and the opening of a file.
#include <iostream.h>
#include <fstream.h>
void main(void)
{
fstream dataFile; // Declare file stream object
char fileName[81];
cout << "Enter the name of a file you wish to openn";
cout << "or create: ";
cin.getline(fileName, 81);
dataFile.open(fileName, ios::out);
cout << "The file " << fileName << " was opened.n";
}

Program Output with Example Input
Enter the name of a file you wish to open
or create: mystuff.dat [Enter]
The file mystuff.dat was opened.

Table 3
File Type Default Open Mode
ofstream The file is opened for output only. (Information may be
written to the file, but not read from the file.) If the file
does not exist, it is created. If the file already exists, its
contents are deleted (the file is truncated).
ifstream The file is opened for input only. (Information may be
read from the file, but not written to it.) The file’s
contents will be read from its beginning. If the file does
not exist, the open function fails.

Table 4
File Mode Flag Meaning
ios::app Append mode. If the file already exists, its
contents are preserved and all output is
written to the end of the file. By default, this
flag causes the file to be created if it does
not exist.
ios::ate If the file already exists, the program goes
directly to the end of it. Output may be
written anywhere in the file.
ios::binary Binary mode. When a file is opened in
binary mode, information is written to or
read from it in pure binary format. (The
default mode is text.)
ios::in Input mode. Information will be read from
the file. If the file does not exist, it will not
be created and the open function will fail.

Table 4 continued
File Mode
Flag
Meaning
ios::nocreate If the file does not already exist, this flag
will cause the open function to fail. (The file
will not be created.)
ios::noreplace If the file already exists, this flag will cause
the open function to fail. (The existing file
will not be opened.)
ios::out Output mode. Information will be written to
the file. By default, the file’s contents will
be deleted if it already exists.
ios::trunc If the file already exists, its contents will be
deleted (truncated). This is the default
mode used by ios::out.

Opening a File at Declaration
fstream dataFile(“names.dat”, ios::in | ios::out);

Program 2
// This program demonstrates the opening of a file at the
// time the file stream object is declared.
void main(void)
{
fstream dataFile("names.dat", ios::in | ios::out);
cout << "The file names.dat was opened.n";
}

The file names.dat was opened.

Testing for Open Errors
dataFile.open(“cust.dat”, ios::in);
if (!dataFile)
{
cout << “Error opening file.n”;
}

Another way to Test for Open Errors
dataFile.open(“cust.dat”, ios::in);
if (dataFile.fail())
{
cout << “Error opening file.n”;
}

Closing a File
• A file should be closed when a program is
finished using it.

Program 3
// This program demonstrates the close function.
void main(void)
{
fstream dataFile;
dataFile.open("testfile.txt", ios::out);
if (!dataFile)
{
cout << "File open error!" << endl;
return;
}
cout << "File was created successfully.n";
cout << "Now closing the file.n";
dataFile.close();
}

Program Output
File was created successfully.
Now closing the file.

7 Using << to Write Information to a
File
• The stream insertion operator (<<) may be
used to write information to a file.
outputFile << “I love C++ programming !”

Program 4
// This program uses the << operator to write information to a file.
void main(void)
{
fstream dataFile;
char line[81];
dataFile.open("demofile.txt", ios::out);
if (!dataFile)
{
return;
}

Program continues
cout << "File opened successfully.n";
cout << "Now writing information to the file.n";
dataFile << "Jonesn";
dataFile << "Smithn";
dataFile << "Willisn";
dataFile << "Davisn";
dataFile.close();
cout << "Done.n";
}

Program Screen Output
File opened successfully.
Now writing information to the file.
Done.
Output to File demofile.txt
Jones
Smith
Willis
Davis

Program 5
// This program writes information to a file, closes the file,
// then reopens it and appends more information.
void main(void)
{
fstream dataFile;
dataFile.open("demofile.txt", ios::out);
dataFile << "Jonesn";
dataFile << "Smithn";
dataFile.close();
dataFile.open("demofile.txt", ios::app);
dataFile << "Willisn";
dataFile << "Davisn";
dataFile.close();
}

Output to File demofile.txt
Jones
Smith
Willis
Davis

8 File Output Formatting
• File output may be formatted the same way as
screen output.

Program 6
// This program uses the precision member function of a
// file stream object to format file output.
void main(void)
{
fstream dataFile;
float num = 123.456;
dataFile.open("numfile.txt", ios::out);
if (!dataFile)
{
return;
}

Program continues
dataFile << num << endl;
dataFile.precision(5);
}

Contents of File numfile.txt
123.456
123.46
123.5
124

Program 7
#include <iomanip.h>
void main(void)
{ fstream outFile("table.txt", ios::out);
int nums[3][3] = { 2897, 5, 837,
34, 7, 1623,
390, 3456, 12 };
// Write the three rows of numbers
for (int row = 0; row < 3; row++)
{
for (int col = 0; col < 3; col++)
{
outFile << setw(4) << nums[row][col] << " ";
}
outFile << endl;
}
outFile.close();
}

Contents of File TABLE.TXT
2897 5 837
34 7 1623
390 3456 12

9 Using >> to Read Information from a
File
• The stream extraction operator (>>) may be
used to read information from a file.

Program 8
// This program uses the >> operator to read information from a file.
void main(void)
{
fstream dataFile;
char name[81];
dataFile.open("demofile.txt", ios::in);
if (!dataFile)
{
return;
}
cout << "Now reading information from the file.nn";

Program continues
for (int count = 0; count < 4; count++)
{
dataFile >> name;
cout << name << endl;
}
dataFile.close();
cout << "nDone.n";
}

File opened successfully.
Now reading information from the file.
Jones
Smith
Willis
Davis
Done.

10 Detecting the End of a File
• The eof() member function reports when
the end of a file has been encountered.
if (inFile.eof())
inFile.close();

Program 9
// This program uses the file stream object's eof() member
// function to detect the end of the file.
void main(void)
{
fstream dataFile;
char name[81];
dataFile.open("demofile.txt", ios::in);
if (!dataFile)
{
return;
}
cout << "Now reading information from the file.nn";

Program continues
dataFile >> name; // Read first name from the file
while (!dataFile.eof())
{
cout << name << endl;
dataFile >> name;
}
dataFile.close();
cout << "nDone.n";
}

Note on eof()
• In C++, “end of file” doesn’t mean the
program is at the last piece of information in
the file, but beyond it. The eof() function
returns true when there is no more
information to be read.

11 Passing File Stream Objects to
Functions
• File stream objects may be passed by reference to
functions.
bool openFileIn(fstream &file, char name[51])
{
bool status;
file.open(name, ios::in);
if (file.fail())
status = false;
else
status = true;
return status;
}

12.12 More Detailed Error Testing
• All stream objects have error state bits that
indicate the condition of the stream.

Table 5
Bit Description
ios::eofbit Set when the end of an input stream is
encountered.
ios::failbit Set when an attempted operation has failed.
ios::hardfail Set when an unrecoverable error has occurred.
ios::badbit Set when an invalid operation has been
attempted.
ios::goodbit Set when all the flags above are not set.
Indicates the stream is in good condition.

Table 6
Function Description
eof() Returns true (non-zero) if the eofbit flag is set,
otherwise returns false.
fail() Returns true (non-zero) if the failbit or hardfail
flags are set, otherwise returns false.
bad() Returns true (non-zero) if the badbit flag is set,
otherwise returns false.
good() Returns true (non-zero) if the goodbit flag is
set, otherwise returns false.
clear() When called with no arguments, clears all the
flags listed above. Can also be called with a
specific flag as an argument.

Program 11
// This program demonstrates the return value of the stream
// object error testing member functions.
// Function prototype
void showState(fstream &);
void main(void)
{
fstream testFile("stuff.dat", ios::out);
if (testFile.fail())
{
cout << "cannot open the file.n";
return;
}

Program continues
int num = 10;
cout << "Writing to the file.n";
testFile << num; // Write the integer to testFile
showState(testFile);
testFile.close(); // Close the file
testFile.open("stuff.dat", ios::in); // Open for input
if (testFile.fail())
{
cout << "cannot open the file.n";
return;
}

Program continues
cout << "Reading from the file.n";
testFile >> num; // Read the only number in the file
cout << "Forcing a bad read operation.n";
testFile >> num; // Force an invalid read operation
testFile.close(); // Close the file
}
// Definition of function ShowState. This function uses
// an fstream reference as its parameter. The return values of
// the eof(), fail(), bad(), and good() member functions are
// displayed. The clear() function is called before the function
// returns.

Program continues
void showState(fstream &file)
{
cout << "File Status:n";
cout << " eof bit: " << file.eof() << endl;
cout << " fail bit: " << file.fail() << endl;
cout << " bad bit: " << file.bad() << endl;
cout << " good bit: " << file.good() << endl;
file.clear(); // Clear any bad bits
}

Program Output
Writing to the file.
File Status:
eof bit: 0
fail bit: 0
bad bit: 0
good bit: 1
Reading from the file.
File Status:
eof bit: 0
fail bit: 0
bad bit: 0
good bit: 1
Forcing a bad read operation.
File Status:
eof bit: 1
fail bit: 2
bad bit: 0
good bit: 0

13 Member Functions for Reading and
Writing Files
• File stream objects have member functions for
more specialized file reading and writing.

Program -12
// This program uses the file stream object's eof() member
// function to detect the end of the file.
void main(void)
{
fstream nameFile;
char input[81];
nameFile.open("murphy.txt", ios::in);
if (!nameFile)
{
return;
}

Program -12 (continued)
nameFile >> input;
while (!nameFile.eof())
{
cout << input;
nameFile >> input;
}
nameFile.close();
}

JayneMurphy47JonesCircleAlmond,NC28702

The getline Member Function
• dataFile.getline(str, 81, ‘n’);
str – This is the name of a character array, or a pointer to a section of
memory. The information read from the file will be stored here.
81 – This number is one greater than the maximum number of
characters to be read. In this example, a maximum of 80
characters will be read.
‘n’ – This is a delimiter character of your choice. If this delimiter is
encountered, it will cause the function to stop reading before it
has read the maximum number of characters. (This argument is
optional. If it’s left our, ‘n’ is the default.)

Program -13
// This program uses the file stream object's getline member
// function to read a line of information from the file.
void main(void)
{
fstream nameFile;
char input[81];
nameFile.open("murphy.txt", ios::in);
if (!nameFile)
{
return;
}

Program continues
nameFile.getline(input, 81); // use n as a delimiter
while (!nameFile.eof())
{
cout << input << endl;
nameFile.getline(input, 81); // use n as a delimiter
}
nameFile.close();
}

Jayne Murphy
47 Jones Circle
Almond, NC 28702

Program -14
// This file shows the getline function with a user-
// specified delimiter.
void main(void)
{
fstream dataFile("names2.txt", ios::in);
char input[81];
dataFile.getline(input, 81, '$');
while (!dataFile.eof())
{
cout << input << endl;
dataFile.getline(input, 81, '$');
}
dataFile.close();
}

Program Output
Jayne Murphy
47 Jones Circle
Almond, NC 28702
Bobbie Smith
217 Halifax Drive
Canton, NC 28716
Bill Hammet
PO Box 121
Springfield, NC 28357

The get Member Function
inFile.get(ch);

Program -15
// This program asks the user for a file name. The file is
// opened and its contents are displayed on the screen.
void main(void)
{
fstream file;
char ch, fileName[51];
cout << "Enter a file name: ";
cin >> fileName;
file.open(fileName, ios::in);
if (!file)
{
cout << fileName << “ could not be opened.n";
return;
}

Program continues
file.get(ch); // Get a character
while (!file.eof())
{
cout << ch;
file.get(ch); // Get another character
}
file.close();
}

The put Member Function
• outFile.put(ch);

Program -16
// This program demonstrates the put member function.
void main(void)
{ fstream dataFile("sentence.txt", ios::out);
char ch;
cout << "Type a sentence and be sure to end it with a ";
cout << "period.n";
while (1)
{
cin.get(ch);
dataFile.put(ch);
if (ch == '.')
break;
}
dataFile.close();
}

Program Screen Output with Example Input
Type a sentence and be sure to end it with a
period.
I am on my way to becoming a great programmer. [Enter]
Resulting Contents of the File SENTENCE.TXT:
I am on my way to becoming a great programmer.

14 Focus on Software Engineering:
Working with Multiple Files
• It’s possible to have more than one file open
at once in a program.

Program -17
// This program demonstrates reading from one file and writing
// to a second file.
#include <ctype.h> // Needed for the toupper function
void main(void)
{
ifstream inFile;
ofstream outFile("out.txt");
char fileName[81], ch, ch2;
cout << "Enter a file name: ";
cin >> fileName;
inFile.open(fileName);
if (!inFile)
{
cout << "Cannot open " << fileName << endl;
return;
}

Program continues
inFile.get(ch); // Get a characer from file 1
while (!inFile.eof()) // Test for end of file
{
ch2 = toupper(ch); // Convert to uppercase
outFile.put(ch2); // Write to file2
inFile.get(ch); // Get another character from file 1
}
inFile.close();
outFile.close();
cout << "File conversion done.n";
}

Enter a file name: hownow.txt [Enter]
File conversion done.
Contents of hownow.txt:
how now brown cow.
How Now?
Resulting Contents of out.txt:
HOW NOW BROWN COW.
HOW NOW?

15 Binary Files
• Binary files contain data that is unformatted,
and not necessarily stored as ASCII text.
file.open(“stuff.dat”, ios::out | ios::binary);

Program -18
// This program uses the write and read functions.
void main(void)
{
fstream file(“NUMS.DAT", ios::out | ios::binary);
int buffer[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
cout << "Now writing the data to the file.n";
file.write((char*)buffer, sizeof(buffer));
file.close();
file.open("NUMS.DAT", ios::in); // Reopen the file.
cout << "Now reading the data back into memory.n";
file.read((char*)buffer, sizeof(buffer));
cout << buffer[count] << " ";
file.close();
}

Now writing the data to the file.
Now reading the data back into memory.
1 2 3 4 5 6 7 8 9 10

16 Creating Records with Structures
• Structures may be used to store fixed-length
records to a file.
struct Info
{
char name[51];
int age;
char address1[51];
char address2[51];
char phone[14];
};
• Since structures can contain a mixture of data
types, you should always use the ios::binary mode
when opening a file to store them.

Program -19
// This program demonstrates the use of a structure variable to
// store a record of information to a file.
#include <ctype.h> // for toupper
// Declare a structure for the record.
struct Info
{
char name[51];
int age;
char address1[51];
char address2[51];
char phone[14];
};

Program continues
void main(void)
{
fstream people("people.dat", ios::out | ios::binary);
Info person;
char again;
if (!people)
{
cout << "Error opening file. Program aborting.n";
return;
}
do
{
cout << "Enter the following information about a ”
<< "person:n";
cout << "Name: ";

Program continues
cin.getline(person.name, 51);
cout << "Age: ";
cin >> person.age;
cin.ignore(); // skip over remaining newline.
cout << "Address line 1: ";
cin.getline(person.address1, 51);
cout << "Address line 2: ";
cin.getline(person.address2, 51);
cout << "Phone: ";
cin.getline(person.phone, 14);
people.write((char *)&person, sizeof(person));
cout << "Do you want to enter another record? ";
cin >> again;
cin.ignore();
} while (toupper(again) == 'Y');
people.close();
}

Enter the following information about a person:
Name: Charlie Baxter [Enter]
Age: 42 [Enter]
Address line 1: 67 Kennedy Bvd. [Enter]
Address line 2: Perth, SC 38754 [Enter]
Phone: (803)555-1234 [Enter]
Do you want to enter another record? Y [Enter]
Enter the following information about a person:
Name: Merideth Murney [Enter]
Age: 22 [Enter]
Address line 1: 487 Lindsay Lane [Enter]
Address line 2: Hazelwood, NC 28737 [Enter]
Phone: (704)453-9999 [Enter]
Do you want to enter another record? N [Enter]

17 Random Access Files
• Random Access means non-sequentially
accessing informaiton in a file.
Figure 12-11

Table -7
Mode Flag Description
ios::beg The offset is calculated from
the beginning of the file.
ios::end The offset is calculated from
the end of the file.
ios::cur The offset is calculated from
the current position.

Table -8
Statement How it Affects the Read/Write Position
File.seekp(32L, ios::beg); Sets the write position to the 33rd byte
(byte 32) from the beginning of the file.
file.seekp(-10L, ios::end); Sets the write position to the 11th byte
(byte 10) from the end of the file.
file.seekp(120L, ios::cur); Sets the write position to the 121st byte
(byte 120) from the current position.
file.seekg(2L, ios::beg); Sets the read position to the 3rd byte
(byte 2) from the beginning of the file.
file.seekg(-100L, ios::end); Sets the read position to the 101st byte
(byte 100) from the end of the file.
file.seekg(40L, ios::cur); Sets the read position to the 41st byte
(byte 40) from the current position.
file.seekg(0L, ios::end); Sets the read position to the end of the
file.

Program -21
// This program demonstrates the seekg function.
void main(void)
{
fstream file("letters.txt", ios::in);
char ch;
file.seekg(5L, ios::beg);
file.get(ch);
cout << "Byte 5 from beginning: " << ch << endl;
file.seekg(-10L, ios::end);
file.get(ch);
cout << "Byte 10 from end: " << ch << endl;

Program continues
file.seekg(3L, ios::cur);
file.get(ch);
cout << "Byte 3 from current: " << ch << endl;
file.close();
}

Byte 5 from beginning: f
Byte 10 from end: q
Byte 3 from current: u

The tellp and tellg Member
Functions
• tellp returns a long integer that is the
current byte number of the file’s write
position.
• tellg returns a long integer that is the
current byte number of the file’s read
position.

Program -23
// This program demonstrates the tellg function.
#include <ctype.h> // For toupper
void main(void)
{
fstream file("letters.txt", ios::in);
long offset;
char ch, again;
do
{
cout << "Currently at position " << file.tellg() << endl;
cout << "Enter an offset from the beginning of the file: ";
cin >> offset;

Program continues
file.seekg(offset, ios::beg);
file.get(ch);
cout << "Character read: " << ch << endl;
cout << "Do it again? ";
cin >> again;
} while (toupper(again) == 'Y');
file.close();
}

Currently at position 0
Enter an offset from the beginning of the file: 5
[Enter]
Character read: f
Do it again? y [Enter]
[Enter]
Character read: a
Do it again? y [Enter]
[Enter]
Character read: u
Do it again? n [Enter]

18 Opening a File for Both Input and
Output
• You may perform input and output on an fstream
file without closing it and reopening it.
fstream file(“data.dat”, ios::in | ios::out);

Program 24
// This program sets up a file of blank inventory records.
// Declaration of Invtry structure
struct Invtry
{
char desc[31];
int qty;
float price;
};
void main(void)
{
fstream inventory("invtry.dat", ios::out | ios::binary);
Invtry record = { "", 0, 0.0 };

Program continues
// Now write the blank records
{
cout << "Now writing record " << count << endl;
inventory.write((char *)&record, sizeof(record));
}
inventory.close();
}

Now writing record 0

Program -25
// This program displays the contents of the inventory file.
struct Invtry
{
char desc[31];
int qty;
float price;
};
void main(void)
{
fstream inventory("invtry.dat", ios::in | ios::binary);
Invtry record = { "", 0, 0.0 };

Program continues
// Now read and display the records
inventory.read((char *)&record, sizeof(record));
while (!inventory.eof())
{
cout << "Description: ";
cout << record.desc << endl;
cout << "Quantity: ";
cout << record.qty << endl;
cout << "Price: ";
cout << record.price << endl << endl;
}
inventory.close();
}

Here is the screen output of Program 12-25 if it is run immediately
after Program 12-24 sets up the file of blank records.
Description:
Quantity: 0
Price: 0.0
Description:
Quantity: 0
Price: 0.0
Description:
Quantity: 0
Price: 0.0
Description:
Quantity: 0
Price: 0.0
Description:
Quantity: 0
Price: 0.0

Program -26
// This program allows the user to edit a specific record in
// the inventory file.
struct Invtry
{
char desc[31];
int qty;
float price;
};
void main(void)
{

Program continues
fstream inventory("invtry.dat", ios::in | ios::out | ios::binary);
Invtry record;
long recNum;
cout << "Which record do you want to edit?";
cin >> recNum;
inventory.seekg(recNum * sizeof(record), ios::beg);
cout << record.desc << endl;
cout << record.qty << endl;
cout << "Price: ";
cout << record.price << endl;
cout << "Enter the new data:n";

Program continues
cin.ignore();
cin.getline(record.desc, 31);
cin >> record.qty;
cout << "Price: ";
cin >> record.price;
inventory.seekp(recNum * sizeof(record), ios::beg);
inventory.write((char *)&record, sizeof(record));
inventory.close();
}

Which record do you ant to edit? 2 [Enter]
Description:
Quantity: 0
Price: 0.0
Enter the new data:
Description: Wrench [Enter]
Quantity: 10 [Enter]
Price: 4.67 [Enter]

References
1. www.tutorialspoint.com/cprogramming/c_pointers.htm
2. www.cprogramming.com/tutorial/c/lesson6.html
3. pw1.netcom.com/~tjensen/ptr/pointers.html
4. Programming in C by yashwant kanitkar
5.ANSI C by E.balagurusamy- TMG publication
6.Computer programming and Utilization by sanjay shah Mahajan Publication
7.www.cprogramming.com/books.html
8.en.wikipedia.org/wiki/C_(programming_language)

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