C++ Input/Output : Streams

In this article, you will learn about Streams Based Input/Output in C++ .

The input/output operations which involve keyboard as input device and screen as output device are known as Console I/O operations . The input/output operations which involve file as input device and output device are known as File I/O operations
C++ Input/Output implement concept of stream .It is an object-oriented alternative to C's FILE-based streams from the C standard library.Stream is the sequences of bytes or flow of data , which acts as a source from which the input data can be obtained by a program or a destination to which the output data can be sent by the program.

Input Stream :

It is flow of data bytes from a device (e.g Keyboard , disk drive) to main memory

Output Stream :

It is flow of data bytes from main memory (i.e program) to a device

Stream Class Hierarchy


Stream class is the collection of data and the methods necessary to control and maintain flow of data or stream .These stream class are declared in the header file iostream.h . The different stream class available in C++ are defined in following hierarchical order.

Unformatted I/O operations

Unformatted I/O operation do not allow user to read or display data in desired format. The unformatted operations supported by C++ are :

Overloaded operator << and >>

The insertion operator (<<) and extraction operator (>>) are overloaded operations which are used for reading and writing data to/from input/output. The predefined object cout is an object of ostream class. The ostream is said to be connected with standard output devices (i.e screen).The cout is used in conjunction with insertion (<<) operator . The C++ compiler also determines the data type of variable to be output ans selects the appropriate stream insertion operator to display data
Syntax

cout<<"message"<varialble;
The predefined object cin is an object of istream class. The istream is said to be connected with standard input devices (i.e keyboard).The cin is used in conjunction with extraction(>>) operator . The C++ compiler also determines the data type of input data ans selects the appropriate stream extraction operator to read data
Syntax
cin>>varialble;

put() and get() functions

The class istream defines get() and ostream defines put() to read and display single character
Syntax
cin.get(character_variable);
cin.put(character_variable);

getline() and write() function

The getline reads the whole line untile the enter key is encountred and write() display the whole line
Syntax
cin.getline(string_variable , size);
cout.write(string , size);


Formatted Console I/O Operations:

Member Functions of ios class and flags :


Member Function Function Syntax
width() The default width of your output will be just enough space to print the number, character, or string in the output buffer. You can change this by using width(). Because width() is a member function, it must be invoked with a cout object. It only changes the width of the very next output field and then immediately reverts to the default. cout.width(w);
Precision() It used to set the number of integers displayed after a decimal point. cout.precision(w);
setf() This is another function of ios class which is used to set various flags used for formatting text in C++ .The function takes two arguments as follows:cout.setf(argument1 ,argument2) where argument1 is one of the formatting flags defined in the class ios , which is used to specify action on the output and argument2 is known as bit field that specifies the group to which the formatting flags belongs
unsetf() This is another function of ios class which is used to unset various flags used for formatting text in C++ .The function takes two arguments as follows:cout.unsetf(argument1)

List of ios flags :

Description of format Flags Bit field
Left justified output ios::left ios:adjusted
Right justified output ios::right ios:adjusted
Padding after sign ios::intrenal ios:adjusted
Scientific notation ios::scientific ios:floatfield
Fixed point notation ios::fixed ios:floatfield
Decimal base ios::dec ios:basefield
Octal base ios::oct ios:basefield
Hexadecimal base ios::hex ios:basefield

Manipulators:

User-defined manipulators:

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