Pure virtual function and File Handling

Virtual Function

Member function of the base class that we expect to redefine in the derived class. It is declared using the virtual keyword. It cannot have static members.

Pure Virtual Function (Do-nothing function)

Function declared in the base class that has no definition relative to the base class. It can be defined as:

virtual<func_type><func_name>() = 0
 
virtual void display() = 0;

Binding

Converts identifier into addresses. Linking function definition to function call.

Early Binding

When compiler acknowledges all the information required to call a function or all its values of the variables during compile time.

Late Binding

Calling a function or assigning a value to a variable at runtime.

Defining opening and closing a file

Types of Stream:

1. Input: ifstream fin; : Stream class to read from files.
2. Output: ofstream fout; : Stream class to write on files.
3. Input/Output: fstream fio; : Stream class to both read and write from/to file.

Opening a File

Using the constructor function of the stream class.

Using the function open.

ifstream fin("file", ios::in);

Closing a File

It is closed by disconnecting it with the stream it is associated with.

stream_object.close();

Input / Output operations on files

To achieve file handling we need the following steps:

1. Naming a file
2. Opening a file
3. Writing data into the file
4. Reading data from the file
5. Closing the file

Classes for File Stream Operations

1. Ios
2. Istream
3. Ostream
4. Streambuf
5. Fstreambase
6. Ifstream
7. Ofstream
8. Fstream
9. Filebuf

Error handling during input/output operations

Error occurs during file handling and C++ has provided built in functions to handle errors during file operations. They are: int bad(), int fail(), int good(), int eof(), etc.

Stream Class Hierarchy for Console Input /Output

Stream Classes in C++ are used to input and output operations on files and io devices. The iostream.h library holds all the stream classes in C++.

Unformatted Input /Output Formatted Input /Output with Ios

Unformatted Input/Output

Reads single input from the user at the console and it allows to display the value at the console. Unformatted I/O are used for character and string datatype but not for another datatypes.

Example: getch(), getchc(), getchar(), putchar(), gets(), puts(), putch(), etc.

Formatted Input /Output

These function takes multiple input from the user and also displays multiple outputs to the users. Format specifiers can be used, so they are called formatted I/O.

Examples: printf(), scanf(), sprintf(), sscanf(), etc.

Formatted IO using class members

The Ios class function contains few format flags used to format the output. It has format flags like showpos, showbase, oct, hex, etc. The format flags are used by the function self().

Function of Ios class used to perform formatted IO in C++ are:

1. width(): The width is used to set the required field width. The output will be displayed in the given width.
2. precision(): set the number of decimal point to a float value
3. fill(): set a character to fill in the blank space of the field
4. setf(): used to set various flags for formatting output
5. unsetf(): remove the flag setting

Formatted IO using Manipulators

The iomanip.h header file contains several special functions that are used to perform formatted IO operations.

Details of special manipulators functions used to perform formatted IO in C++ are:

1. setw(): Equivalent of width()
2. setprecision(): Equivalent of precision()
3. setfill(): Equivalent of fill()
4. setiosflags(): Equivalent of setf()
5. resetiosflags(): Equivalent of unsetf()

The iomanip.h also contains the following format flags using in formatted IO in C++.

Member functions and Flags

Formatting with Manipulators

Manipulators

They are operators that are used to format the data display.

Two types of manipulators

1. Manipulators with Arguments: requires iomanip header.
2. Manipulators without Arguments: requires iostream header.