Library Functions: get( ) and put() Functions

Library Functions:

C++ offers two categories of functions that can be implemented in your program. 1. Library functions 2. User-defined function. For now we will just focus on Library Functions. So, before we can proceed further it is required to know about the terms Library and Function.

Library:

A collection of sub programs (functions) used to develop other programs and software is known as Library.  C++ library of functions stores function definitions in some categories e.g. standard input-output functions, string function, I/O manipulator functions, mathematical function etc) under separate files known as header files. Header files can be identified with .h extension as a part of their file name.

Function:

A Function is a named set of program instruction; designed to do certain task. A function can have list of arguments, which represents the information being passed to the function and also it can have return data type.

            So, by now we can say that - The functions whose definition of work or activity is already been defined in the system is called Library Function. A library function can be accessed by simply writing the function name, followed by a list of arguments (depends on function prototype), which represent the information being passed to the function.

Example:

char ch = getch( );//defined in conio.h

Header File:

C++ standard library contains files containing function prototypes, definitions, data types and constants for standard library functions.  These are known as header files. These header files have .h extension as a part of their file name.

Example: stdio.h, string.h, math.h, stdlib.h, iostream.h, iomanip.h etc.

Character I/O Functions:

So, far in our previous programs and sample codes we have seen the use of cin and cout these are the I/O operators which gives you formatting control over the input and output, but these are not character I/O functions. The functions which let’s you to read / write character by character is called character I/O function.

get( ):

The get() inputs a single character from the standard input device (by default it is keyboard). Syntax: device.get(char_variable); The device can be any standard input device. If you want to get input from a keyboard then you should use cin as the device. Because, most of the computers consider the keyboard as the standard input device, stdin.

Example:

char ch;

cin.get(ch);

     The get( ) function is a buffered input function. When you type in, data does not go into your program unless you hit Enter key. As it is said earlier, get( ) function receives one character, including white space, at a time from the input stream. Here you should remember, an input stream can be a standard input stream object or user defined stream object of the istream class.

Example:

//Sample code illustrating the use of user-defined stream object with get()

ifstream infile;

infile.open(“PARA.TXT”);

char ch;

int count=0;

while(infile)

{

infile.get(ch);/*get()is used with object ‘infile’ of class ifstream,                 

              reading character by character from a disk file*/        

if(isdigit(ch))

count++;

}

infile.close();

cout<<”\n Total digits = “<<count;

put( ):

Syntax: device.put(char_variable);

put( ) function sends one character at a time to the output stream, where an output stream can be a standard output stream object or user-defined output stream object.

Example:

#include<iostream.h>

#include<conio.h>

#include<stdio.h>

#include<fstream.h>

void main()

{

clrscr();

char string[50];

cout<<"\n Enter an string to write in a file";

gets(string);

fstream FILE;

FILE.open("MYTEXT.TXT",ios::app);

     for(int i=0;string[i]!='\0';i++)

     {

      FILE.put(string[i]);/* writing one-by-one character from 

                            character array to a disk file named 

                            as "MYTEXT.TXT"*/

     }

FILE.close();

getch();

}

Output:

In the above program put() function is used with user-defined output stream object (FILE) which represents a disk file “MYTEXT.TXT”.

Example 2:

char ch = ‘X’;

cout.put(ch); /*Writes character ‘X’ on the standard output stream, sends output to stdout

                                    (Standard output device – Screen)*/

To use get( ) or put( )function with user-defined input / output stream object, it is required to use “fstream.h” header file in your program, otherwise including “iostream.h” is enough to use cin / cout respectively.

Note**

More discussion on get( ) and put( ) functions and using them with user-defined input/output stream object will be discussed later. For now it is out of the scope of this session. 

            In my next post I will write about some more character I/O function – getchar(), putchar(), getch() and putch().