Data File Handling In C++

Data File Handling In C++

File. The information / data stored under a specific name on a storage device, is called a file.

Stream. It refers to a sequence of bytes.

Text file. It is a file that stores information in ASCII characters. In text files, each line of text is terminated with a special character known as EOL (End of Line) character or delimiter character. When this EOL character is read or written, certain internal translations take place.

Binary file. It is a file that contains information in the same format as it is held in memory. In binary files, no delimiters are used for a line and no translations occur here.    

Classes for file stream operation

ofstream: Stream class to write on files
ifstream: Stream class to read from files
fstream: Stream class to both read and write from/to files.

Opening a file

OPENING FILE USING CONSTRUCTOR
ofstream fout(“results”);    //output only
ifstream fin(“data”);  //input only

OPENING FILE USING open()
Stream-object.open(“filename”, mode)

      ofstream ofile;
      ofile.open(“data1”);
     
      ifstream ifile;
      ifile.open(“data2”);

File mode parameter	Meaning
ios::app	Append to end of file
ios::ate	go to end of file on opening
ios::binary	file open in binary mode
ios::in	open file for reading only
ios::out	open file for writing only
ios::nocreate	open fails if the file does not exist
ios::noreplace	open fails if the file already exist
ios::trunc	delete the contents of the file if it exist

All these flags can be combined using the bitwise operator OR (|). For example, if we want to open the file example.bin in binary mode to add data we could do it by the following call to member function open():

fstream file;
file.open ("example.bin", ios::out | ios::app | ios::binary);

Closing File

   fout.close();
   fin.close();

INPUT AND OUTPUT OPERATION

put() and get() function
the function put() writes a single character to the associated stream. Similarly, the function get() reads a single character form the associated stream.
example :
file.get(ch);
file.put(ch);

write() and read() function
write() and read() functions write and read blocks of binary data.
example:
file.read((char *)&obj, sizeof(obj));
file.write((char *)&obj, sizeof(obj));

ERROR HANDLING FUNCTION

FUNCTION	RETURN VALUE AND MEANING
eof()	returns true (non zero) if end of file is encountered while reading; otherwise return false(zero)
fail()	return true when an input or output operation has failed
bad()	returns true if an invalid operation is attempted or any unrecoverable error has occurred.
good()	returns true if no error has occurred.

File Pointers And Their Manipulation

All i/o streams objects have, at least, one internal stream pointer:
ifstream, like istream, has a pointer known as the get pointer that points to the element to be read in the next input operation.

ofstream, like ostream, has a pointer known as the put pointer that points to the location where the next element has to be written.

Finally, fstream, inherits both, the get and the put pointers, from iostream (which is itself derived from both istream and ostream).

These internal stream pointers that point to the reading or writing locations within a stream can be manipulated using the following member functions:

seekg()	moves get pointer(input) to a specified location
seekp()	moves put pointer (output) to a specified location
tellg()	gives the current position of the get pointer
tellp()	gives the current position of the put pointer

The other prototype for these functions is:

seekg(offset, refposition );
seekp(offset, refposition );

The parameter offset represents the number of bytes the file pointer is to be moved from the location specified by the parameter refposition. The refposition takes one of the following three constants defined in the ios class.

ios::beg          start of the file
ios::cur          current position of the pointer
ios::end          end of the file

example:
file.seekg(-10, ios::cur);

2

Basic Operation On Text File In C++

Program to write in a text file

#include<fstream.h>
int main()
{
     ofstream fout;
     fout.open("out.txt");
     char str[300]="Time is a great teacher but unfortunately it kills all its pupils. Berlioz";
     fout<<str;
     fout.close();
     return 0;
}

Program to read from text file and display it

#include<fstream.h>
#include<conio.h>
int main()
{
     ifstream fin;
     fin.open("out.txt");
     char ch;
     while(!fin.eof())
     {
          fin.get(ch);
          cout<<ch;
     }
     fin.close();
     getch();
     return 0;
}

Program to count number of characters.

#include<fstream.h>
#include<conio.h>
int main()
{
     ifstream fin;
     fin.open("out.txt");
     clrscr();
     char ch; int count=0;
     while(!fin.eof())
     {
          fin.get(ch);
          count++;
     }
     cout<<"Number of characters in file is "<<count;
     fin.close();
     getch();
     return 0;
}

Program to count number of words

#include<fstream.h>
#include<conio.h>
int main()
{
     ifstream fin;
     fin.open("out.txt");
     char word[30]; int count=0;
     while(!fin.eof())
     {
          fin>>word;
          count++;
     }
     cout<<"Number of words in file is "<<count;
     fin.close();
     getch();
     return 0;
}

Program to count number of lines

#include<fstream.h>
#include<conio.h>
int main()
{
     ifstream fin;
     fin.open("out.txt");
     char str[80]; int count=0;
     while(!fin.eof())
     {
          fin.getline(str,80);
          count++;
     }
     cout<<"Number of lines in file is "<<count;
     fin.close();
     getch();
     return 0;
}

Program to copy contents of file to another file.

#include<fstream.h>
int main()
{
     ifstream fin;
     fin.open("out.txt");
     ofstream fout;
     fout.open("sample.txt");
     char ch;
     while(!fin.eof())
     {
          fin.get(ch);
          fout<<ch;
     }
     fin.close();
     return 0;
}

Basic Operation On Binary File In C++

class student
{
            int admno;
            char name[20];
public:
          void getdata()
          {
                     cout<<"\nEnter The admission no. ";
                     cin>>admno;
                     cout<<"\n\nEnter The Name of The Student ";
                     gets(name);
          }
          void showdata()
          {
                     cout<<"\nAdmission no. : "<<admno;
                     cout<<"\nStudent Name : ";
                     puts(name);
          }
          int retadmno()
          {
                     return admno;
          }
};

function to write in a binary file

void write_data()
{
          student obj;
          ofstream fp2;
          fp2.open("student.dat",ios::binary|ios::app);
          obj.getdata();
          fp2.write((char*)&obj,sizeof(obj));
          fp2.close();
}

function to display records of file

void display()
{
          student obj;
          ifstream fp1;
          fp1.open("student.dat",ios::binary);
          while(fp1.read((char*)&obj,sizeof(obj)))
          {
                     obj.showdata();
          }
}
          fp.close();
}

Function to search and display from binary file

void search (int n)
{
          student obj;
          ifstream fp1;
          fp1.open("student.dat",ios::binary);
          while(fp1.read((char*)&obj,sizeof(obj)))
          {
                     if(obj.retadmno()==n)
                                obj.showdata();
          }
          fp1.close();
}

Function to delete a record

void deleterecord(int n)
{
          student obj;
          ifstream fp1;
          fp1.open("student.dat",ios::binary);
          ofstream fp2;
          fp2.open("Temp.dat",ios::out|ios::binary);
          while(fp1.read((char*)&obj,sizeof(obj)))
          {
                      if(obj.retadmno!=n)
                                    fp2.write((char*)&obj,sizeof(obj));
          }
          fp1.close();
          fp2.close();
          remove("student.dat");
          rename("Temp.dat","student.dat");
}

Function to modify a record

void modifyrecord(int n)
{
          fstream fp;
          student obj;
          int found=0;
          fp.open("student.dat",ios::in|ios::out);
          while(fp.read((char*)&obj,sizeof(obj)) && found==0)
          {
                     if(obj.retadmno()==n)
                     {
                              obj.showdata();
                              cout<<"\nEnter The New Details of student";
                              obj.getdata();
                              int pos=-1*sizeof(obj);
                              fp.seekp(pos,ios::cur);
                              fp.write((char*)&obj,sizeof(obj));
                              found=1;
                    }
          }
          fp.close();
}

Pointers c++

Pointer

C++ Memory Map

Once a program is compiled, C++ creates four logically distinct regions of memory:
Code Area : Area to hold the compiled program code
Data Area : Area to hold global variables
Stack Area : Area to hold the return address of function calls, argument passed to the functions, local variables for functions and the current state of the CPU.
Heap : Area from which the memory is dynamically allocated to the program.

Accessing address of a variable

Computer’s memory is organized as a linear collection of bytes. Every byte in the computer’s memory has an address. Each variable in program is stored at a unique address. We can use address operator & to get address of a variable:
            int num = 23;
            cout << &num;       // prints address in hexadecimal

POINTER

A pointer is a variable that holds a memory address, usually the location of another variable in memory.

Defining a Pointer Variable
            int *iptr;
iptr can hold the address of an int

Pointer Variables Assignment:
 int num = 25;
 int *iptr;
 iptr = &num;

Memory layout

To access num using iptr and indirection operator *
     cout << iptr;        // prints 0x4a00
     cout << *itptr;     // prints 25     

Similary, following declaration shows:
char *cptr;
float *fptr;
cptr is a pointer to character and fptr is a pointer to float value.

Pointer Arithmetic

Some arithmetic operators can be used with pointers:
   - Increment and decrement operators ++, --
    - Integers can be added to or subtracted from
      pointers using the operators +, -, +=, and -=

Each time a pointer is incremented by 1, it points to the memory location of the next element of its base type.
If “p” is a character pointer then “p++” will increment “p” by 1 byte.
If “p” were an integer pointer its value on “p++” would be incremented by 2 bytes.

Pointers and Arrays

Array name is base address of array
            int vals[] = {4, 7, 11};
            cout << vals;       // displays 0x4a00
            cout << vals[0]; // displays 4

Lets takes an example:

int arr[]={4,7,11};
int *ptr = arr;
What is ptr + 1?         
It means (address in ptr) + (1 * size of an int)
cout << *(ptr+1); // displays 7
cout << *(ptr+2); // displays 11

Array Access
Array notation  arr[i]  is equivalent to the pointer notation  *(arr + i)

Assume the variable definitions
   int arr[]={4,7,11};
   int *ptr = arr;
Examples of use of ++ and --
   ptr++; // points at 7
   ptr--; // now points at 4

Character Pointers and Strings

Initialize to a character string.
char* a = “Hello”;
a is pointer to the memory location where  ‘H’ is stored. Here “a” can be viewed as a character array of size 6, the only difference being that a can be reassigned another memory location.
 char* a = “Hello”;
 a          gives address of ‘H’
*a        gives ‘H’
a[0]      gives ‘H’
a++      gives address of ‘e’
*a++     gives ‘e’

Pointers as Function Parameters

A pointer can be a parameter. It works like a reference parameter to allow change to argument from within function

Pointers as Function Parameters
       void swap(int *x, int *y)
       {   
          int temp;
                              temp = *x;
                              *x = *y;
                              *y = temp;
       }
      swap(&num1, &num2);

Pointers to Constants and Constant Pointers

Pointer to a constant: cannot change the value that is pointed at
Constant pointer: address in pointer cannot change once pointer is initialized

Pointers to Structures

We can create pointers to structure variables

            struct Student {int rollno; float fees;};
            Student stu1;
            Student *stuPtr = &stu1;
            (*stuPtr).rollno= 104;
-or-
Use the form ptr->member:
            stuPtr->rollno = 104;

Static allocation of memory

In the static memory allocation, the amount of memory to be allocated is predicted and preknown. This memory is allocated during the compilation itself. All the declared variables declared normally, are allocated memory statically.

Dynamic allocation of memory

In the dynamic memory allocation, the amount of memory to be allocated is not known. This memory is allocated during run-time as and when required. The memory is dynamically allocated using new operator.

Free store

Free store is a pool of unallocated heap memory given to a program that is used by the program for dynamic allocation during execution.

Dynamic Memory Allocation

We can allocate storage for a variable while program is running by using new operator

To allocate memory of type integer
int *iptr=new int;

To allocate array
double *dptr = new double[25];

To allocate dynamic structure variables or objects
Student sptr = new Student;    //Student is tag name of structure

Releasing Dynamic Memory

Use delete to free dynamic memory
delete iptr;
To free dynamic array memory
delete [] dptr;
To free dynamic structure
delete Student;

Memory Leak

If the objects, that are allocated memory dynamically, are not deleted using delete, the memory block remains occupied even at the end of the program. Such memory blocks are known as orphaned memory blocks. These orphaned memory blocks when increase in number, bring adverse effect on the system. This situation is called memory leak

Self Referential Structure

The self referential structures are structures that include an element that is a pointer to another structure of the same type.

struct node
{
  int data;
  node* next;
}

Class & Objects c++

Class & Objects

The mechanism that allows you to combine data and the function in a single unit is called a class. Once a class is defined, you can declare variables of that type. A class variable is called object or instance. In other words, a class would be the data type, and an object would be the variable. Classes are generally declared using the keyword class, with the following format:

class class_name

{

    private:

        members1;

    protected:

        members2;

    public:

        members3;

};

Where class name is a valid identifier for the class. The body of the declaration can contain members, that can be either data or function declarations, The members of a class are classified into three categories: private, public, and protected. private, protected, and public are reserved words and are called member access specifiers. These specifiers modify the access rights that the members following them acquire.

private members of a class are accessible only from within other members of the same class. You cannot access it outside of the class.
protected members are accessible from members of their same class and also from members of their derived classes.
Finally, public members are accessible from anywhere where the object is visible.

By default, all members of a class declared with the class keyword have private access for all its members. Therefore, any member that is declared before one other class specifier automatically has private access.

Here is a complete example :

class Circle

{

    private:

        double radius;

    public:

        void setRadius(double r)

        {

            radius = r;

        }

        double getArea()

        {

            return 3.14 * radius * radius;

        }

};

Object Declaration

Once a class is defined, you can declare objects of that type. The syntax for declaring an object is the same as that for declaring any other variable. The following statements declare two objects of type circle:

Circle c1, c2;

Accessing Class Members

Once an object of a class is declared, it can access the public members of the class.

c1.setRadius(2.5);

Defining Member function of class

You can define Functions inside the class as shown in above example. Member functions defined inside a class this way are created as inline functions by default. It is also possible to declare a function within a class but define it elsewhere. Functions defined outside the class are not normally inline.
When we define a function outside the class we cannot reference them (directly) outside of the class. In order to reference these, we use the scope resolution operator, :: (double colon). In this example, we are defining function setRadius outside the class:

void Circle :: setRadius(double r)

{

    radius = r;

}

The following program demostrates the general feature of classes. Member funcitons setRadius() and getArea() defined outside the class.

#include <iostream>

using namespace std;

class Circle{

    private :

        double radius;    public:

        void setRadius(double r);

        double getArea();};

void Circle :: setRadius(double r)

{

    radius = r;

}

double Circle :: getArea()

{

    return 3.14 * radius * radius;

}

int main()

{

    Circle c1;    c1.setRadius(2.5);    cout<<c1.getArea();    return 0;

}