A stream is a sequence of bytes. A stream is a general name given to a flow of data. Different streams are used to represent different kinds of data flow. Each stream is associated with a particular class,which contains member functions and definitions for dealing with that particular kind of data flow. The stream that supplies data to the program in known as input stream. It reads the data from the file and hands it over to the program. The stream that receives data from the program is known as output stream. It writes the received data to the file.Following figure illustrates it.
When the main function of your program is invoked, it already has three predefined streams open and available for use. These represent the "standard" input and output channels that have been established for the process.
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