starting out with c++, 3 rd edition basic file operations in c++ dr. ahmed telba

Starting Out with C++, 3rd Edition

Basic file operations in C++

Dr. Ahmed Telba


2

Chapter – File Operations


3

12.1 What is a File?

• A file is a collection on information, usually stored on a computer’s disk. Information can be saved to files and then later reused.


4

12.2 File Names

• All files are assigned a name that is used for identification purposes by the operating system and the user.


5

Table 12-1File Name and Extension File Contents

M Y P R O G .B A S BASIC program

M E N U .B A T DOS Batch File

IN S T A L L .D O C Documentation File

C R U N C H .E X E Executable File

B O B .H T M L HTML (Hypertext Markup Language) File

3 D M O D E L .JA V A Java program or applet

IN V E N T .O B J Object File

P R O G 1 .P R J Borland C++ Project File

A N S I.S Y S System Device Driver

R E A D M E .T X T Text File


6

12.3 Focus on Software Engineering: The Process of Using a File

• Using a file in a program is a simple three-step process– The file must be opened. If the file does not yet

exits, opening it means creating it.– Information is then saved to the file, read from

the file, or both.– When the program is finished using the file, the

file must be closed.


7

Figure 12-1


8

Figure 12-2


9

12.4 Setting Up a Program for File Input/Output

• Before file I/O can be performed, a C++ program must be set up properly.

• File access requires the inclusion of fstream.h


10

12.5 Opening a File

• Before data can be written to or read from a file, the file must be opened.

ifstream inputFile;

inputFile.open(“customer.dat”);


11

Program 12-1// This program demonstrates the declaration of an fstream// object and the opening of a file.#include <iostream.h> #include <fstream.h>

void main(void){

fstream dataFile; // Declare file stream objectchar fileName[81];cout << "Enter the name of a file you wish to open\n";cout << "or create: ";cin.getline(fileName, 81);dataFile.open(fileName, ios::out);cout << "The file " << fileName << " was opened.\n";

}


12

Program Output with Example Input

Enter the name of a file you wish to openor create: mystuff.dat [Enter]The file mystuff.dat was opened.


13

Table 12-3

File Type Default Open Mode

o fs tre a m The file is opened for output only. (Information may bewritten to the file, but not read from the file.) If the filedoes not exist, it is created. If the file already exists, itscontents are deleted (the file is truncated).

ifs tre a m The file is opened for input only. (Information may beread from the file, but not written to it.) The file’scontents will be read from its beginning. If the file doesnot exist, the open function fails.


14

Table 12-4File Mode Flag Meaning

io s ::ap p Append mode. If the file already exists, itscontents are preserved and all output iswritten to the end of the file. By default, thisflag causes the file to be created if it doesnot exist.

io s ::a te If the file already exists, the program goesdirectly to the end of it. Output may bewritten anywhere in the file.

io s ::b in a ry Binary mode. When a file is opened inbinary mode, information is written to orread from it in pure binary format. (Thedefault mode is text.)

io s ::in Input mode. Information will be read fromthe file. If the file does not exist, it will notbe created and the open function will fail.


15

Table 12-4 continued

File ModeFlag

Meaning

io s ::n o c rea te If the file does not already exist, this flagwill cause the open function to fail. (The filewill not be created.)

io s ::n o rep lace If the file already exists, this flag will causethe open function to fail. (The existing filewill not be opened.)

io s ::o u t Output mode. Information will be written tothe file. By default, the file’s contents willbe deleted if it already exists.

io s ::tru n c If the file already exists, its contents will bedeleted (truncated). This is the defaultmode used by ios::out.


16

Opening a File at Declaration

fstream dataFile(“names.dat”, ios::in | ios::out);


17

Program 12-2

// This program demonstrates the opening of a file at the// time the file stream object is declared.#include <iostream.h>#include <fstream.h>

main( ){

fstream dataFile("names.txt", ios::in | ios::out);cout << "The file names.dat was opened.\n";

system("PAUSE");}


18


The file names.dat was opened.


19

Testing for Open Errors

dataFile.open(“cust.txt”, ios::in);

if (!dataFile)

{

cout << “Error opening file.\n”;

}


20

Another way to Test for Open Errors

dataFile.open(“cust.dat”, ios::in);

if (dataFile.fail())

{

cout << “Error opening file.\n”;

}


21

12.6 Closing a File

• A file should be closed when a program is finished using it.


// writing on a text file

• // writing on a text file• #include <iostream>• #include <fstream>• using namespace std;

• int main () {• ofstream myfile ("example.txt");• if (myfile.is_open())• {• myfile << "This is a new file created in cpp.\n";• myfile << "This is another line.\n";• myfile.close();• }• else cout << "Unable to open file";• system("pause");• return 0;• }


// reading a text file

• // reading a text file• #include <iostream>• #include <fstream>• #include <string>• using namespace std;

• int main () {• string line;• ifstream myfile ("example.txt");• if (myfile.is_open())• {• while ( getline (myfile,line) )• {• cout << line << endl;• }• myfile.close();• }

• else cout << "Unable to open file"; • system("pause");• return 0;• }


file operations in C++• #include <fstream>

• using namespace std;

• int main ()

• { ofstream myfile;

• myfile.open ("example22.txt");

• myfile << "Writing this to a file.\n";

• myfile<<"Hope fine”" << endl;

• myfile<<"this frist file ”" << endl;

• myfile.close();

• system("pause");

• return 0; }Slide 6- 24


• #include <fstream>

• #include <iostream>


• int main()

• { char FirstName[30], LastName[30];

• int Age;

• char FileName[20];

• cout << "Enter First Name: ";

• cin >> FirstName;

• cout << "Enter Last Name: ";

• cin >> LastName;

• cout << "Enter Age: ";

• cin >> Age;

• cout << "\nEnter the name of the file you want to create: ";

• cin >> FileName;

• ofstream Students(FileName, ios::out);

• Students << FirstName << "\n" << LastName << "\n" << Age;

• cout << "\n\n";


• return 0;

• }

Slide 6- 25


• // basic file operations• #include <iostream>• #include <fstream>• using namespace std;

• int main () {• ofstream myfile;• myfile.open ("example.txt");• myfile << "Writing this to a file.\n";• myfile.close();• system("pause");• return 0;• }

Slide 6- 26


Write to file

• #include<iostream.h>• #include <fstream.h>• int main()• { ofstream fout;• fout.open("D:\\firstExa.txt");• fout << "Asalamualikom hope fine .\n"• << "WELCOME TO GE 211 FILE SECTION PROGRAM\n"• << "HOPE TO DO WELL IN SECOND MEDTERM EXAM\

n";• fout.close();• system("pause");• }


• //Write the odd number in file• #include<iostream.h>• #include <fstream.h>• int main()• { ofstream fout;• fout.open("D:\\firstExa.txt");• int i,j;• for(i=2;i<30;i+=2)• fout<<i<<"\t";• fout.close();• system("pause");• }


• // print in file Even number 1:30• #include<iostream.h>• #include <fstream.h>• int main()• { ofstream fout;• fout.open("D:\\firstExa.txt");• int i,j;• for(i=1;i<30;i+=2)• fout<<i<<"\t";• fout.close();• system("pause");• }


• #include<iostream.h>• #include <fstream.h>• main()• {ofstream fout;• fout.open("D:\\ffffff.txt");• float i,j,m,sum;• j=3;• sum=0;• for(i=1;i<=100;i++){• m=(i*i)/(j*j);• j=j+2;• sum=sum+m;}• cout<<"seque="<<sum<<endl;• fout<<"seque="<<sum<<endl;• fout.close();• system("pause");}


• //write equation for this series • #include<iostream.h>• main()• {• int i,j,m,n,sum;• sum=0;• cin>>n;• for(i=1 ;i<=n ;i++)• {• m=i*i;• sum=sum+m; } • cout<< "seque="<<sum<< endl;• system("pause");• }


• #include<iostream.h>• #include <fstream.h>• #include<cmath>• main()• {• float i,m,n,b,a,y,x,s;• y=0;• b=2;• cout<<"enter the last power of\n";• cin>>n;• cout<<"enter the volue of(x)\n";• cin>>s;• for(i=1;i<=n;i++){• x=pow(s,i);• a=pow(b,i);• m=x/a;• y=y+m;• }• cout<<"y= "<<y;• system("pause");• }


• #include<iostream.h>• #include <fstream.h>• #include<cmath>• main()• {ofstream fout;• fout.open("D:\\UUUU.txt");

• float i,m,n,b,a,y,x,s;• y=0;• b=2;• cout<<"enter the last power of\n";• cin>>n;• cout<<"enter the volue of(x)\n";• cin>>s;• for(i=1;i<=n;i++){• x=pow(s,i);• a=pow(b,i);• m=x/a;• y=y+m;• }• cout<<"y= "<<y;• fout<<"y= "<<y;• fout.close();• system("pause");• }


• //Fenonci seris • #include<iostream.h>• #include <fstream.h>• main()• {ofstream fout;• fout.open("D:\\finoncy.txt");• int i,s,b,d ;• s=0;• d=1;• for(i=0;i<20;i++)• {• b=s;• s=d;• d=s+b;• fout<<d<<"\t";• }• fout.close();• system("pause");}


• //write to file • #include<iostream.h>• #include <fstream.h>• main()• {• ofstream fout;• fout.open("D:\\Seris.txt");

• int i,j,m,n,sum;• sum=0;• cin>>n;• for(i=1 ;i<=n ;i++)• {• m=i*i;• sum=sum+m; } • fout<< "seque="<<sum<< endl;• fout.close();• system("pause");• }


Read from file

• #include <fstream.h>• #include <iostream.h>• main()• { char array [80];• ifstream fin;• fin.open("D:\\firstExa.txt");• while(!fin.eof())• {fin.getline(array,80);• cout<<array<<endl;}• fin.close();• system("pause"); }


FLAGES IN FILE

• FLAGES IN FILE


Write in binary file

• ofstream fout ;

• fout.open("file path",iostream family

• fout.write((char*)& data ,sizeo(data);


Binary form

• #include<iostream.h>• #include <fstream.h>• main()• { int Array[80],i;• for(i=0;i<10;i++)• cin>> Array[i];• ofstream fout;• fout.open("D:\\ahmed.bin",ios::binary);• fout .write((char *) & Array , sizeof(Array));• fout.close();• system("pause");• }



• int main () {• ofstream myfile ("example.txt");• if (myfile.is_open())• {• myfile << "This is a line.\n";• myfile << "This is another line.\n";• myfile.close();• }• else cout << "Unable to open file";• system("pause");• return 0;• }

Slide 6- 40


• // reading a text file



• #include <string>


• int main () {

• string line;

• ifstream myfile ("example.txt");

• if (myfile.is_open())

• {

• while ( myfile.good() )

• {

• getline (myfile,line);

• cout << line << endl;

• }

• myfile.close();

• }

• else cout << "Unable to open file";


• return 0;

• }

Slide 6- 41


Slide 6- 42

I/O Streams

• I/O refers to program input and output

– Input is delivered to your program via a stream object

– Input can be from• The keyboard

• A file

– Output is delivered to the output device via a streamobject

– Output can be to • The screen

• A file


Using fout

Slide 6- 43



• #include <cstdlib>


• int main (int aaa,char *avg[])

• {

• ofstream fout ("my_out.txt");

• fout<<" Assalamualikom Hope fine" << endl;

• fout<<"Please tray good in second exam this frist file " << endl;


• return 0;}


Write in file • #include <fstream>• #include <iostream>• using namespace std;

• int main( )• {

• //cout<<"Exam1\n";• // ifstream ;// read• // ofstream ;// write• // fstream;//read &write• ofstream myfile;• myfile.open("kkkk.txt");• myfile<< "Exam1 is ok\n";• myfile<< "please tray good in second exam";• myfile.close();• system("pause");• return 0;• }


Using fstream

• #include <fstream>• #include <iostream>• using namespace std;


• /*cout<<"Exam1\n";• // ifstream ;// read• // ofstream ;// write• // fstream;//read &write*/• fstream myfile;• myfile.open("kkkk.txt",ios ::out);

• //myfile<< "Exam1 is ok\n";• myfile<< "please tray good in second exam****************";• //cout<<myfile.rdbuf();• myfile.close();

• system("pause");• return 0;• }


Using app

• #include <fstream>• #include <iostream>• using namespace std;


• /*cout<<"Exam1\n";• ifstream ;// read• ofstream ;// write• fstream;//read &write*/• fstream myfile;• myfile.open("kkkk.txt",ios ::out|ios::app);

• //myfile<< "Exam1 is ok\n";• myfile<< "please tray good in second exam****************\n";• //cout<<myfile.rdbuf();• myfile.close();



Read from file• #include <fstream>• #include <iostream>• using namespace std;


• /*cout<<"Exam1\n";• ifstream ;// read• ofstream ;// write• fstream;//read &write*/• ifstream myfile;• myfile.open("kkkk.txt");

• //myfile<< "Exam1 is ok\n";• //myfile<< "please tray good in second exam";• cout<<myfile.rdbuf();• myfile.close();



Input &Output with files

• Input / Output with files

• C++ provides the following classes to perform output and input of characters to/from files:

• 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.


• // basic file operations• #include <iostream>• #include <fstream>• using namespace std;

• int main () {• ofstream myfile;• myfile.open ("example.txt");• myfile << "Writing this to a file.\n";• myfile.close();• return 0;• }


class default mode parameter

ofstream ios::out

ifstream ios::in

fstream ios::in | ios::out

ofstream myfile;myfile.open ("example.bin", ios::out | ios::app | ios::binary);


Basic file operations

• // basic file operations• #include <iostream>• #include <fstream>• //#include <ifstream>• //#include <ofstream>


• int main () {• ofstream myfile;• myfile.open ("XXX.txt");• myfile << "**Writing this to a file.\n";• myfile << "****Writing this to a file.\n";• myfile << "*********Writing this to a file.\n";• myfile.close();• system("PAUSE");• return 0;• }


Basic file operations

• #include <iostream>• #include <fstream>• using namespace std;

• int main (int argc, char *arvg[ ]) • {• ofstream fout("XXX.txt");• fout << "**Writing this to a file.\n";• fout << "****Writing this to a file.\n";• fout << "*********Writing this to a file.\n";• system("PAUSE");• return EXIT_SUCCESS;• }


FILE IN C++

ios::in Open for input operations.

ios::out Open for output operations.

ios::binary Open in binary mode.

ios::ateSet the initial position at the end of the file.If this flag is not set to any value, the initial position is the beginning of the file.

ios::app

All output operations are performed at the end of the file, appending the content to the current content of the file. This flag can only be used in streams open for output-only operations.

ios::truncIf the file opened for output operations already existed before, its previous content is deleted and replaced by the new one.



• int main () {• ofstream myfile ("example.txt");• if (myfile.is_open())• {• myfile << "This is a line.\n";• myfile << "This is another line.\n";• myfile.close();• }• else cout << "Unable to open file";• return 0;• }


• Open a file

• The first operation generally performed on an object of one of these classes is to associate it to a real file. This procedure is known as to open a file.

• An open file is represented within a program by a stream object (an instantiation of one of these classes, in the previous example this was myfile) and any input or output operation performed on this stream object will be applied to the physical file associated to it.

• In order to open a file with a stream object we use its member function open():

• open (filename, mode);

• Where filename is a null-terminated character sequence of type const char * (the same type that string literals have) representing the name of the file to be opened, and mode is an optional parameter with a combination of the following flags:


• IOS :: IN OPEN FILE FOR READ

•


61

Program 12-3// This program demonstrates the close function.#include <iostream.h>#include <fstream.h>void main(void){

fstream dataFile;dataFile.open("testfile.txt", ios::out);if (!dataFile){

cout << "File open error!" << endl;return;

}cout << "File was created successfully.\n";cout << "Now closing the file.\n";dataFile.close();

}


62

Program Output

File was created successfully.Now closing the file.


63

12.7 Using << to Write Information to a File

• The stream insertion operator (<<) may be used to write information to a file.

outputFile << “I love C++ programming !”


64

Program 12-4// This program uses the << operator to write information

to a file.#include <iostream.h>#include <fstream.h>

void main(void){

fstream dataFile;char line[81];

dataFile.open("demofile.txt", ios::out);if (!dataFile){


}


65

Program continues

cout << "File opened successfully.\n";cout << "Now writing information to the file.\n";dataFile << "Jones\n";dataFile << "Smith\n";dataFile << "Willis\n";dataFile << "Davis\n";dataFile.close();cout << "Done.\n";

}


66

Program Screen Output

File opened successfully.Now writing information to the file.Done.

Output to File demofile.txtJonesSmithWillisDavis


67

Figure 12-3


68

Program 12-5// This program writes information to a file, closes the file,// then reopens it and appends more information.#include <iostream.h>#include <fstream.h>void main(void){

fstream dataFile;

dataFile.open("demofile.txt", ios::out);dataFile << "Jones\n";dataFile << "Smith\n";dataFile.close();dataFile.open("demofile.txt", ios::app);dataFile << "Willis\n";dataFile << "Davis\n";dataFile.close();

}


69

Output to File demofile.txt

JonesSmithWillisDavis


70

12.8 File Output Formatting

• File output may be formatted the same way as screen output.


71

Program 12-6// This program uses the precision member function of a// file stream object to format file output.#include <iostream.h>#include <fstream.h>

void main(void){

fstream dataFile;float num = 123.456;dataFile.open("numfile.txt", ios::out);if (!dataFile){


}


72

Program continues

dataFile << num << endl;dataFile.precision(5);dataFile << num << endl;dataFile.precision(4);dataFile << num << endl;dataFile.precision(3);dataFile << num << endl;

}


73

Contents of File numfile.txt

123.456123.46123.5124


74

Program 12-7#include <iostream.h> #include <fstream.h>#include <iomanip.h>void main(void){ fstream outFile("table.txt", ios::out);

int nums[3][3] = { 2897, 5, 837, 34, 7, 1623, 390, 3456, 12 };// Write the three rows of numbersfor (int row = 0; row < 3; row++){

for (int col = 0; col < 3; col++){

outFile << setw(4) << nums[row][col] << " ";}outFile << endl;

}outFile.close();

}


75

Contents of File TABLE.TXT

2897 5 837 34 7 1623 390 3456 12


76

Figure 12-6


77

12.9 Using >> to Read Information from a File

• The stream extraction operator (>>) may be used to read information from a file.


78

Program 12-8

// This program uses the >> operator to read information from a file.

#include <iostream.h> #include <fstream.h>

void main(void){

fstream dataFile;char name[81];dataFile.open("demofile.txt", ios::in);if (!dataFile){


}cout << "File opened successfully.\n";cout << "Now reading information from the file.\n\n";


79

Program continues

for (int count = 0; count < 4; count++){

dataFile >> name;cout << name << endl;

}dataFile.close();cout << "\nDone.\n";

}


80


File opened successfully.Now reading information from the file.

JonesSmithWillisDavis

Done.


81

12.10 Detecting the End of a File

• The eof() member function reports when the end of a file has been encountered.

if (inFile.eof())

inFile.close();


82

Program 12-9// This program uses the file stream object's eof() member// function to detect the end of the file.#include <iostream.h> #include <fstream.h>void main(void){

fstream dataFile;char name[81];dataFile.open("demofile.txt", ios::in);if (!dataFile){


}cout << "File opened successfully.\n";cout << "Now reading information from the file.\n\n";


83

Program continues

dataFile >> name; // Read first name from the filewhile (!dataFile.eof()){

cout << name << endl;dataFile >> name;

}dataFile.close();cout << "\nDone.\n";

}


84


File opened successfully.Now reading information from the file.

JonesSmithWillisDavisDone.


85

Note on eof()

• In C++, “end of file” doesn’t mean the program is at the last piece of information in the file, but beyond it. The eof() function returns true when there is no more information to be read.


86

12.11 Passing File Stream Objects to Functions• File stream objects may be passed by reference to

functions.bool openFileIn(fstream &file, char name[51]){ bool status;

file.open(name, ios::in); if (file.fail()) status = false; else status = true; return status;}


87

12.12 More Detailed Error Testing

• All stream objects have error state bits that indicate the condition of the stream.


88

Table 12-5

Bit Description

io s::eo fb it Set when the end of an input stream isencountered.

io s ::fa ilb it Set when an attempted operation has failed.

io s ::h a rd fa il Set when an unrecoverable error has occurred.

io s ::b a d b it Set when an invalid operation has beenattempted.

io s ::g o o d b it Set when all the flags above are not set.Indicates the stream is in good condition.


89

Table 12-6Function Description

eo f() Returns true (non-zero) if the eofbit flag is set,otherwise returns false.

fa il() Returns true (non-zero) if the failbit or hardfailflags are set, otherwise returns false.

b ad () Returns true (non-zero) if the badbit flag is set,otherwise returns false.

g o o d () Returns true (non-zero) if the goodbit flag isset, otherwise returns false.

c lea r() When called with no arguments, clears all theflags listed above. Can also be called with aspecific flag as an argument.


90

Program 12-11// This program demonstrates the return value of the stream// object error testing member functions.#include <iostream.h> #include <fstream.h>// Function prototypevoid showState(fstream &);

void main(void){

fstream testFile("stuff.dat", ios::out);if (testFile.fail()){

cout << "cannot open the file.\n";return;

}


91

Program continues

int num = 10;cout << "Writing to the file.\n";testFile << num; // Write the integer to testFileshowState(testFile);testFile.close(); // Close the filetestFile.open("stuff.dat", ios::in); // Open for inputif (testFile.fail()){

cout << "cannot open the file.\n";return;

}


92

Program continues

cout << "Reading from the file.\n";testFile >> num; // Read the only number in the fileshowState(testFile);cout << "Forcing a bad read operation.\n";testFile >> num; // Force an invalid read operationshowState(testFile);testFile.close(); // Close the file

}

// Definition of function ShowState. This function uses// an fstream reference as its parameter. The return values of// the eof(), fail(), bad(), and good() member functions are // displayed. The clear() function is called before the function// returns.


93

Program continues

void showState(fstream &file){

cout << "File Status:\n";cout << " eof bit: " << file.eof() << endl;cout << " fail bit: " << file.fail() << endl;cout << " bad bit: " << file.bad() << endl;cout << " good bit: " << file.good() << endl;file.clear(); // Clear any bad bits

}


94

Program OutputWriting to the file.File Status: eof bit: 0 fail bit: 0 bad bit: 0 good bit: 1Reading from the file.File Status: eof bit: 0 fail bit: 0 bad bit: 0 good bit: 1Forcing a bad read operation.File Status: eof bit: 1 fail bit: 2 bad bit: 0 good bit: 0


95

12.13 Member Functions for Reading and Writing Files

• File stream objects have member functions for more specialized file reading and writing.


96

Figure 12-8


97

Program 12-12// This program uses the file stream object's eof() member// function to detect the end of the file.#include <iostream.h> #include <fstream.h>

void main(void){

fstream nameFile;char input[81];

nameFile.open("murphy.txt", ios::in);if (!nameFile){


}


98

Program 12-12 (continued)

nameFile >> input;while (!nameFile.eof()){

cout << input;nameFile >> input;

}nameFile.close();

}


99


JayneMurphy47JonesCircleAlmond,NC28702


100

The getline Member Function

• dataFile.getline(str, 81, ‘\n’);str – This is the name of a character array, or a pointer to a

section of memory. The information read from the file will be stored here.

81 – This number is one greater than the maximum number of characters to be read. In this example, a maximum of 80 characters will be read.

‘\n’ – This is a delimiter character of your choice. If this delimiter is encountered, it will cause the function to stop reading before it has read the maximum number of characters. (This argument is optional. If it’s left our, ‘\n’ is the default.)


101

Program 12-13// This program uses the file stream object's getline member// function to read a line of information from the file.


void main(void){

fstream nameFile;char input[81];

nameFile.open("murphy.txt", ios::in);if (!nameFile){


}


102

Program continues

nameFile.getline(input, 81); // use \n as a delimiterwhile (!nameFile.eof()){

cout << input << endl;nameFile.getline(input, 81); // use \n as a

delimiter}nameFile.close();

}


103


Jayne Murphy47 Jones CircleAlmond, NC 28702


104

Program 12-14// This file shows the getline function with a user-// specified delimiter.

#include <iostream.h> #include <fstream.h>void main(void){

fstream dataFile("names2.txt", ios::in);char input[81];

dataFile.getline(input, 81, '$');while (!dataFile.eof()){

cout << input << endl;dataFile.getline(input, 81, '$');

}dataFile.close();

}


105

Program Output

Jayne Murphy47 Jones CircleAlmond, NC 28702

Bobbie Smith217 Halifax DriveCanton, NC 28716

Bill HammetPO Box 121

Springfield, NC 28357


106

The get Member Function

inFile.get(ch);


107

Program 12-15// This program asks the user for a file name. The file is // opened and its contents are displayed on the screen.#include <iostream.h> #include <fstream.h>

void main(void){

fstream file;char ch, fileName[51];cout << "Enter a file name: ";cin >> fileName;file.open(fileName, ios::in);if (!file){

cout << fileName << “ could not be opened.\n";return;

}


108

Program continues

file.get(ch); // Get a characterwhile (!file.eof()){

cout << ch;file.get(ch); // Get another character

}file.close();

}


109

The put Member Function

• outFile.put(ch);


110

Program 12-16// This program demonstrates the put member function.#include <iostream.h> #include <fstream.h>

void main(void){ fstream dataFile("sentence.txt", ios::out);

char ch;

cout << "Type a sentence and be sure to end it with a ";cout << "period.\n";while (1){

cin.get(ch);dataFile.put(ch);if (ch == '.') break;

}dataFile.close();

}


111

Program Screen Output with Example Input

Type a sentence and be sure to end it with aperiod.

I am on my way to becoming a great programmer. [Enter]

Resulting Contents of the File SENTENCE.TXT:

I am on my way to becoming a great programmer.


112

12.14 Focus on Software Engineering: Working with Multiple Files

• It’s possible to have more than one file open at once in a program.


113

Program 12-17// This program demonstrates reading from one file and writing// to a second file.#include <iostream.h> #include <fstream.h>#include <ctype.h> // Needed for the toupper function

void main(void){

ifstream inFile;ofstream outFile("out.txt");char fileName[81], ch, ch2;

cout << "Enter a file name: ";cin >> fileName;inFile.open(fileName);if (!inFile){

cout << "Cannot open " << fileName << endl;return;

}


114

Program continuesinFile.get(ch); // Get a characer from file 1while (!inFile.eof()) // Test for end of file{

ch2 = toupper(ch); // Convert to uppercaseoutFile.put(ch2); // Write to file2

inFile.get(ch); // Get another character from file 1}inFile.close();outFile.close();cout << "File conversion done.\n";

}


115


Enter a file name: hownow.txt [Enter]

File conversion done.

Contents of hownow.txt:how now brown cow.

How Now?

Resulting Contents of out.txt:HOW NOW BROWN COW.

HOW NOW?


116

12.15 Binary Files

• Binary files contain data that is unformatted, and not necessarily stored as ASCII text.file.open(“stuff.dat”, ios::out | ios::binary);


117

Figure 12-9


118

Figure 12-10


119

Program 12-18// This program uses the write and read functions.#include <iostream.h> #include <fstream.h>

void main(void){

fstream file(“NUMS.DAT", ios::out | ios::binary);int buffer[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};

cout << "Now writing the data to the file.\n";file.write((char*)buffer, sizeof(buffer));file.close();file.open("NUMS.DAT", ios::in); // Reopen the file.cout << "Now reading the data back into memory.\n";file.read((char*)buffer, sizeof(buffer));for (int count = 0; count < 10; count++)

cout << buffer[count] << " ";file.close();

}


120


Now writing the data to the file.Now reading the data back into memory.

1 2 3 4 5 6 7 8 9 10


121

12.16 Creating Records with Structures

• Structures may be used to store fixed-length records to a file.

struct Info{ char name[51]; int age; char address1[51]; char address2[51]; char phone[14];};

• Since structures can contain a mixture of data types, you should always use the ios::binary mode when opening a file to store them.


122

Program 12-19// This program demonstrates the use of a structure variable to// store a record of information to a file.

#include <iostream.h> #include <fstream.h>#include <ctype.h> // for toupper

// Declare a structure for the record.struct Info{

char name[51];int age;char address1[51];char address2[51];char phone[14];

};


123

Program continues

void main(void){

fstream people("people.dat", ios::out | ios::binary);Info person;char again;if (!people){

cout << "Error opening file. Program aborting.\n";return;

}

do{

cout << "Enter the following information about a ”<< "person:\n";

cout << "Name: ";


124

Program continuescin.getline(person.name, 51);cout << "Age: ";cin >> person.age;cin.ignore(); // skip over remaining newline.cout << "Address line 1: ";cin.getline(person.address1, 51);cout << "Address line 2: ";cin.getline(person.address2, 51);cout << "Phone: ";cin.getline(person.phone, 14);people.write((char *)&person, sizeof(person));cout << "Do you want to enter another record? ";cin >> again;cin.ignore();

} while (toupper(again) == 'Y');people.close();

}


125

Program Screen Output with Example InputEnter the following information about a person:Name: Charlie Baxter [Enter]Age: 42 [Enter]Address line 1: 67 Kennedy Bvd. [Enter]Address line 2: Perth, SC 38754 [Enter]Phone: (803)555-1234 [Enter]Do you want to enter another record? Y [Enter]Enter the following information about a person:Name: Merideth Murney [Enter]Age: 22 [Enter]Address line 1: 487 Lindsay Lane [Enter]Address line 2: Hazelwood, NC 28737 [Enter]Phone: (704)453-9999 [Enter]

Do you want to enter another record? N [Enter]


126

12.17 Random Access Files

• Random Access means non-sequentially accessing informaiton in a file.

Figure 12-11


127

Table 12-7

Mode Flag Description

io s ::b e g The offset is calculated fromthe beginning of the file.

io s ::en d The offset is calculated fromthe end of the file.

io s ::cu r The offset is calculated fromthe current position.


128

Table 12-8

Statement How it Affects the Read/Write Position

F ile .see k p (3 2 L , io s ::b eg ); Sets the write position to the 33rd byte (byte 32) from the beginning of the file.

file .see k p (-1 0 L , io s ::en d ); Sets the write position to the 11th byte (byte 10) from the end of the file.

file .see k p (1 2 0 L , io s ::cu r) ; Sets the write position to the 121st byte (byte 120) from the current position.

file .see k g (2 L , io s ::b eg ); Sets the read position to the 3rd byte (byte 2) from the beginning of the file.

file .see k g (-1 0 0 L , io s ::en d ); Sets the read position to the 101st byte (byte 100) from the end of the file.

file .see k g (4 0 L , io s ::cu r); Sets the read position to the 41st byte (byte 40) from the current position.

file .see k g (0 L , io s ::en d ); Sets the read position to the end of the file.


129

Program 12-21// This program demonstrates the seekg function.


void main(void){

fstream file("letters.txt", ios::in);char ch;

file.seekg(5L, ios::beg);file.get(ch);cout << "Byte 5 from beginning: " << ch << endl;file.seekg(-10L, ios::end);file.get(ch);cout << "Byte 10 from end: " << ch << endl;


130

Program continues

file.seekg(3L, ios::cur);file.get(ch);cout << "Byte 3 from current: " << ch << endl;file.close();

}


131


Byte 5 from beginning: fByte 10 from end: q

Byte 3 from current: u


132

The tellp and tellg Member Functions

• tellp returns a long integer that is the current byte number of the file’s write position.

• tellg returns a long integer that is the current byte number of the file’s read position.


133

Program 12-23// This program demonstrates the tellg function.#include <iostream.h> #include <fstream.h>#include <ctype.h> // For toupper

void main(void){

fstream file("letters.txt", ios::in);long offset;char ch, again;

do{

cout << "Currently at position " << file.tellg() << endl;cout << "Enter an offset from the beginning of the file:

";cin >> offset;


134

Program continues

file.seekg(offset, ios::beg);file.get(ch);cout << "Character read: " << ch << endl;cout << "Do it again? ";cin >> again;

} while (toupper(again) == 'Y');file.close();

}


135


Currently at position 0Enter an offset from the beginning of the file: 5 [Enter]Character read: fDo it again? y [Enter]Currently at position 6Enter an offset from the beginning of the file: 0 [Enter]Character read: aDo it again? y [Enter]Currently at position 1Enter an offset from the beginning of the file: 20 [Enter]Character read: u

Do it again? n [Enter]


136

12.18 Opening a File for Both Input and Output

• You may perform input and output on an fstream file without closing it and reopening it.

fstream file(“data.dat”, ios::in | ios::out);


137

Program 12-24// This program sets up a file of blank inventory records.#include <iostream.h>#include <fstream.h>

// Declaration of Invtry structurestruct Invtry{

char desc[31];int qty;float price;

};

void main(void){

fstream inventory("invtry.dat", ios::out | ios::binary);Invtry record = { "", 0, 0.0 };


138

Program continues

// Now write the blank recordsfor (int count = 0; count < 5; count++){

cout << "Now writing record " << count << endl;inventory.write((char *)&record, sizeof(record));

}inventory.close();

}


139


Now writing record 0Now writing record 1Now writing record 2Now writing record 3

Now writing record 4


140

Program 12-25// This program displays the contents of the inventory file.#include <iostream.h>#include <fstream.h>



};

void main(void){

fstream inventory("invtry.dat", ios::in | ios::binary);Invtry record = { "", 0, 0.0 };


141

Program continues

// Now read and display the recordsinventory.read((char *)&record, sizeof(record));while (!inventory.eof()){

cout << "Description: ";cout << record.desc << endl;cout << "Quantity: ";cout << record.qty << endl;cout << "Price: ";cout << record.price << endl << endl;inventory.read((char *)&record, sizeof(record));

}inventory.close();

}


142

Here is the screen output of Program 12-25 if it is run immediately after Program 12-24 sets up the file of blank records.

Program Screen OutputDescription:Quantity: 0Price: 0.0Description:Quantity: 0Price: 0.0Description:Quantity: 0Price: 0.0Description:Quantity: 0Price: 0.0Description:Quantity: 0Price: 0.0


143

Program 12-26// This program allows the user to edit a specific record in// the inventory file.#include <iostream.h>#include <fstream.h>



};

void main(void){


144

Program continues

fstream inventory("invtry.dat", ios::in | ios::out | ios::binary);Invtry record;long recNum;cout << "Which record do you want to edit?";cin >> recNum;inventory.seekg(recNum * sizeof(record), ios::beg);inventory.read((char *)&record, sizeof(record));cout << "Description: ";cout << record.desc << endl;cout << "Quantity: ";cout << record.qty << endl;cout << "Price: ";cout << record.price << endl;cout << "Enter the new data:\n";cout << "Description: ";


145

Program continues

cin.ignore();cin.getline(record.desc, 31);cout << "Quantity: ";cin >> record.qty;cout << "Price: ";cin >> record.price;inventory.seekp(recNum * sizeof(record), ios::beg);inventory.write((char *)&record, sizeof(record));inventory.close();

}


146


Which record do you ant to edit? 2 [Enter]Description:Quantity: 0Price: 0.0Enter the new data:Description: Wrench [Enter]Quantity: 10 [Enter]

Price: 4.67 [Enter]


Copyright © 2008 Pearson Addison-Wesley. All rights reserved.

Chapter 6

I/O Streams as an Introduction to Objects and Classes


Slide 6- 149

Overview

6.1 Streams and Basic File I/O

6.2 Tools for Stream I/O

6.3 Character I/O



6.1

Streams and Basic File I/O


Slide 6- 151

I/O Streams

• I/O refers to program input and output

– Input is delivered to your program via a stream object

– Input can be from• The keyboard

• A file

– Output is delivered to the output device via a streamobject

– Output can be to • The screen

• A file


Slide 6- 152

Objects

• Objects are special variables that– Have their own special-purpose functions– Set C++ apart from earlier programming

languages


Slide 6- 153

Streams and Basic File I/O

• Files for I/O are the same type of files used tostore programs

• A stream is a flow of data.

– Input stream: Data flows into the program• If input stream flows from keyboard, the program will

accept data from the keyboard

• If input stream flows from a file, the program will acceptdata from the file

– Output stream: Data flows out of the program• To the screen

• To a file


Slide 6- 154

cin And cout Streams

• cin– Input stream connected to the keyboard

• cout – Output stream connected to the screen

• cin and cout defined in the iostream library– Use include directive: #include <iostream>

• You can declare your own streams to use with

files.


Slide 6- 155

Why Use Files?

• Files allow you to store data permanently!

• Data output to a file lasts after the program ends

• An input file can be used over and over

– No typing of data again and again for testing

• Create a data file or read an output file at yourconvenience

• Files allow you to deal with larger data sets


Slide 6- 156

File I/O

• Reading from a file

– Taking input from a file

– Done from beginning to the end (for now)• No backing up to read something again (OK to start over)

• Just as done from the keyboard

• Writing to a file

– Sending output to a file

– Done from beginning to end (for now)• No backing up to write something again( OK to start over)

• Just as done to the screen


Slide 6- 157

Stream Variables

• Like other variables, a stream variable… – Must be declared before it can be used– Must be initialized before it contains valid data

• Initializing a stream means connecting it to a file

• The value of the stream variable can be thought of as the file it is connected to

– Can have its value changed• Changing a stream value means disconnecting from

one file and connecting to another


Slide 6- 158

Streams and Assignment

• A stream is a special kind of variable called an object

– Objects can use special functions to complete tasks

• Streams use special functions instead of the assignment operator to change values


Slide 6- 159

Declaring An Input-file Stream Variable

• Input-file streams are of type ifstream

• Type ifstream is defined in the fstream library

– You must use the include and using directives #include <fstream> using namespace std;

• Declare an input-file stream variable using ifstream in_stream;


Slide 6- 160

Declaring An Output-file Stream Variable

• Ouput-file streams of are type ofstream

• Type ofstream is defined in the fstream library

– You must use these include and using directives #include <fstream> using namespace std;

• Declare an input-file stream variable using ofstream out_stream;


Slide 6- 161

• Once a stream variable is declared, connect it toa file– Connecting a stream to a file is opening the file– Use the open function of the stream object

in_stream.open("infile.dat");

Period

File name on the disk

Double quotes

Connecting To A File


Slide 6- 162

Using The Input Stream

• Once connected to a file, the input-stream variable can be used to produce input just asyou would use cin with the extraction operator– Example:

int one_number, another_number; in_stream >> one_number >> another_number;


Slide 6- 163

Using The Output Stream

• An output-stream works similarly to the input-stream– ofstream out_stream;

out_stream.open("outfile.dat");

out_stream << "one number = " << one_number << "another number = " << another_number;


Slide 6- 164

External File Names

• An External File Name…

– Is the name for a file that the operating system uses• infile.dat and outfile.dat used in the previous examples

– Is the "real", on-the-disk, name for a file

– Needs to match the naming conventions on your system

– Usually only used in the stream's open statement

– Once open, referred to using the name of the stream connected to it.


• After using a file, it should be closed

– This disconnects the stream from the file

– Close files to reduce the chance of a file being corrupted if the program terminates abnormally

• It is important to close an output file if your program later needs to read input from the output file

• The system will automatically close files if you forget as long as your program ends normally

Slide 6- 165

Display 6.1

Closing a File


Slide 6- 166

Objects

• An object is a variable that has functions and data associated with it– in_stream and out_stream each have a function

named open associated with them– in_stream and out_stream use different

versions of a function named open • One version of open is for input files• A different version of open is for output files


Slide 6- 167

Member Functions

• A member function is a function associated withan object– The open function is a member function of

in_stream in the previous examples– A different open function is a member function

of out_stream in the previous examples


Slide 6- 168

Objects and Member Function Names

• Objects of different types have different member functions

– Some of these member functions might have the same name

• Different objects of the same type have the same member functions


Slide 6- 169

Classes

• A type whose variables are objects, is a class

– ifstream is the type of the in_stream variable (object)

– ifstream is a class

– The class of an object determines its member functions

– Example: ifstream in_stream1, in_stream2;

• in_stream1.open and in_stream2.open are the samefunction but might have different arguments


Slide 6- 170

Class Member Functions

• Member functions of an object are the memberfunctions of its class

• The class determines the member functions ofthe object

– The class ifstream has an open function

– Every variable (object) declared of type ifstream has that open function


Slide 6- 171

Calling object

Dot operator

Member function

Calling a Member Function

• Calling a member function requires specifying the object containing the function

• The calling object is separated from the member function by the dot operator

• Example: in_stream.open("infile.dat");


Slide 6- 172

Member Function Calling Syntax

• Syntax for calling a member function:

Calling_object.Member_Function_Name(Argument_list);


Slide 6- 173

Errors On Opening Files

• Opening a file could fail for several reasons– Common reasons for open to fail include

• The file might not exist

• The name might be typed incorrectly

• May be no error message if the call to open fails– Program execution continues!


Slide 6- 174

Catching Stream Errors

• Member function fail, can be used to test the success of a stream operation– fail returns a boolean type (true or false)– fail returns true if the stream operation failed


Slide 6- 175

Halting Execution

• When a stream open function fails, it is generally best to stop the program

• The function exit, halts a program

– exit returns its argument to the operating system

– exit causes program execution to stop

– exit is NOT a member function

• Exit requires the include and using directives #include <cstdlib> using namespace std;


• Immediately following the call to open, check that the operation was successful:

in_stream.open("stuff.dat"); if( in_stream.fail( ) ) { cout << "Input file opening failed.\n"; exit(1) ; }

Slide 6- 176

Display 6.2

Using fail and exit


Slide 6- 177

Techniques for File I/O

• When reading input from a file…

– Do not include prompts or echo the input• The lines cout << "Enter the number: ";

cin >> the_number; cout << "The number you

entered is " << the_number;become just one line

in_file >> the_number;

– The input file must contain exactly the data expected


• Output examples so far create new files

– If the output file already contains data, that datais lost

• To append new output to the end an existing file

– use the constant ios::app defined in the iostream library: outStream.open("important.txt", ios::app);

– If the file does not exist, a new file will be created

Slide 6- 178

Display 6.3

Appending Data (optional)


Slide 6- 179

File Names as Input (optional)

• Program users can enter the name of a file to use for input or for output

• Program must use a variable that can hold multiple characters – A sequence of characters is called a string – Declaring a variable to hold a string of characters:

char file_name[16];• file_name is the name of a variable• Brackets enclose the maximum number of characters + 1 • The variable file_name contains up to 15 characters


• char file_name[16];cout << "Enter the file_name ";cin >> file_name;ifstream in_stream;in_stream.open(file_name);if (in_stream.fail( ) ){ cout << "Input file opening failed.\n"; exit(1);}

Slide 6- 180

Display 6.4 (1)

Display 6.4 (2)

Using A Character String


Slide 6- 181

Section 6.1 Conclusion

• Can you

– Write a program that uses a stream called fin which will be connected to an input file and a stream calledfout which will be connected to an output file? Howdo you declare fin and fout? What include directive, if any, do you nee to place in yourprogram file?

– Name at least three member functions of an iostream object and give examples of usage of each?



6.2

Tools for Streams I/O


Slide 6- 183

Tools for Stream I/O

• To control the format of the program's output – We use commands that determine such details as:

• The spaces between items• The number of digits after a decimal point• The numeric style: scientific notation for fixed point• Showing digits after a decimal point even if they are

zeroes• Showing plus signs in front of positive numbers• Left or right justifying numbers in a given space


Slide 6- 184

Formatting Output to Files

• Format output to the screen with: cout.setf(ios::fixed);

cout.setf(ios::showpoint); cout.precision(2);

• Format output to a file using the out-file stream named out_stream with:

out_stream.setf(ios::fixed);out_stream.setf(ios::showpoint);

out_stream.precision(2);


Slide 6- 185

out_stream.precision(2);

• precision is a member function of output streams

– After out_stream.precision(2);Output of numbers with decimal points…

• will show a total of 2 significant digits 23. 2.2e7 2.2 6.9e-10.00069OR

• will show 2 digits after the decimal point23.56 2.26e7 2.21 0.69 0.69e-4

• Calls to precision apply only to the streamnamed in the call


Slide 6- 186

setf(ios::fixed);

• setf is a member function of output streams

– setf is an abbreviation for set flags• A flag is an instruction to do one of two options

• ios::fixed is a flag

– After out_stream.setf(ios::fixed);All further output of floating point numbers…

• Will be written in fixed-point notation, the way we normally expect to see numbers

• Calls to setf apply only to the stream named inthe call


• After out_stream.setf(ios::showpoint);

Output of floating point numbers…• Will show the decimal point even if all digits after

thedecimal point are zeroes

Slide 6- 187

Display 6.5

setf(ios::showpoint);


Slide 6- 188

7 7

(ios::right) (ios::left)

Creating Space in Output

• The width function specifies the number of spaces for the next item

– Applies only to the next item of output

• Example: To print the digit 7 in four spaces use out_stream.width(4); out_stream << 7 << endl;

– Three of the spaces will be blank


Slide 6- 189

Not Enough Width?

• What if the argument for width is too small?– Such as specifying

cout.width(3); when the value to print is 3456.45

• The entire item is always output– If too few spaces are specified, as many more

spaces as needed are used


Slide 6- 190

Unsetting Flags

• Any flag that is set, may be unset

• Use the unsetf function– Example:

cout.unsetf(ios::showpos);

causes the program to stop printing plus signs on positive numbers


Slide 6- 191

Manipulators

• A manipulator is a function called in a nontraditional way– Manipulators in turn call member functions– Manipulators may or may not have arguments– Used after the insertion operator (<<) as if the

manipulator function call is an output item


Slide 6- 192

Two Spaces Four Spaces

The setw Manipulator

• setw does the same task as the member function width

– setw calls the width function to set spaces for output

• Example: cout << "Start" << setw(4) << 10 << setw(4) << setw(6) << 30;

produces: Start 10 20 30


Slide 6- 193

The setprecision Manipulator

• setprecision does the same task as the member function precision

• Example: cout.setf(ios::fixed); cout.setf(ios::showpoint); cout << "$" << setprecision(2)

<< 10.3 << endl<< "$" << 20.5 << endl;

produces: $10.30

$20.50– setprecision setting stays in effect until changed


Slide 6- 194

Manipulator Definitions

• The manipulators setw and setprecision are defined in the iomanip library– To use these manipulators, add these lines

#include <iomanip>using namespace std;


Slide 6- 195

Stream Names as Arguments

• Streams can be arguments to a function– The function's formal parameter for the stream

must be call-by-reference

• Example: void make_neat(ifstream& messy_file, ofstream& neat_file);


Slide 6- 196

The End of The File

• Input files used by a program may vary in length

– Programs may not be able to assume the numberof items in the file

• A way to know the end of the file is reached:

– The boolean expression (in_stream >> next)• Reads a value from in_stream and stores it in next

• True if a value can be read and stored in next

• False if there is not a value to be read (the end of the file)


Slide 6- 197

End of File Example

• To calculate the average of the numbers in a file– double next, sum = 0;

int count = 0; while(in_stream >> next) {

sum = sum + next; count++; }

double average = sum / count;


Slide 6- 198

Stream Arguments and Namespaces

• Using directives have been local to function definitions in the examples so far

• When parameter type names are in a namespace

– A using directive must be outside the function soC++ will understand the parameter type names suchas ifstream

• Easy solution is to place the using directive at thebeginning of the file

– Many experts do not approve as this does not allow using multiple namespaces with names in common


• The program in Display 6.6…

– Takes input from rawdata.dat

– Writes output to the screen and to neat.dat• Formatting instructions are used to create a neater layout

• Numbers are written one per line in a field width of 12

• Each number is written with 5 digits after the decimal point

• Each number is written with a plus or minus sign

– Uses function make_neat that has formal parametersfor the input-file stream and output-file stream

Slide 6- 199

Display 6.6 (1) Display 6.6 (2) Display 6.6 (3)

Program Example


Slide 6- 200


• Can you– Show the output produced when the following

line is executed?

cout << "*" << setw(3) << 12345 << "*" endl;

– Describe the effect of each of these flags?Ios::fixed ios::scientific ios::showpointios::right ios::right ios::showpos



6.3

Character I/O


Slide 6- 202

Character I/O

• All data is input and output as characters

– Output of the number 10 is two characters '1' and '0'

– Input of the number 10 is also done as '1' and '0'

– Interpretation of 10 as the number 10 or as charactersdepends on the program

– Conversion between characters and numbers isusually automatic


Slide 6- 203

Low Level Character I/O

• Low level C++ functions for character I/O– Perform character input and output – Do not perform automatic conversions– Allow you to do input and output in anyway

youcan devise


Slide 6- 204

Member Function get

• Function get– Member function of every input stream– Reads one character from an input stream– Stores the character read in a variable of type

char, the single argument the function takes– Does not use the extraction operator (>>)

which performs some automatic work– Does not skip blanks


Slide 6- 205

Using get

• These lines use get to read a character and store it in the variable next_symbol

char next_symbol; cin.get(next_symbol);

– Any character will be read with these statements• Blank spaces too!

• '\n' too! (The newline character)


Slide 6- 206

get Syntax

• input_stream.get(char_variable);

• Examples: char next_symbol;cin.get(next_symbol);

ifstream in_stream;in_stream.open("infile.dat");in_stream.get(next_symbol);


Slide 6- 207

More About get

• Given this code: char c1, c2, c3;cin.get(c1);cin.get(c2);cin.get(c3);

and this input: AB CD

• c1 = 'A' c2 = 'B' c3 = '\n'– cin >> c1 >> c2 >> c3; would place 'C' in c3

(the ">>" operator skips the newline character)


Slide 6- 208

The End of The Line

• To read and echo a line of input– Look for '\n' at the end of the input line:

cout<<"Enter a line of input and I will " << "echo it.\n";

char symbol; do { cin.get(symbol); cout << symbol;

} while (symbol != '\n');– All characters, including '\n' will be output


Slide 6- 209

'\n ' vs "\n "

• '\n'– A value of type char– Can be stored in a variable of type char

• "\n"– A string containing only one character– Cannot be stored in a variable of type char

• In a cout-statement they produce the same result


Slide 6- 210

Member Function put

• Function put– Member function of every output stream– Requires one argument of type char– Places its argument of type char in the output

stream– Does not do allow you to do more than

previous output with the insertion operator and cout


Slide 6- 211

put Syntax

• Output_stream.put(Char_expression);

• Examples: cout.put(next_symbol); cout.put('a');

ofstream out_stream; out_stream.open("outfile.dat"); out_stream.put('Z');


Slide 6- 212

Member Function putback

• The putback member function places a character in the input stream

– putback is a member function of every input stream

– Useful when input continues until a specific characteris read, but you do not want to process the character

– Places its argument of type char in the input stream

– Character placed in the stream does not have tobe a character read from the stream


Slide 6- 213

putback Example

• The following code reads up to the first blank in the input stream fin, and writes the characters tothe file connected to the output stream fout– fin.get(next);

while (next != ' ') { fout.put(next); fin.get(next); } fin.putback(next);

– The blank space read to end the loop is put back into the input stream


Slide 6- 214

Program ExampleChecking Input

• Incorrect input can produce worthless output

• Use input functions that allow the user to re-enter input until it is correct, such as– Echoing the input and asking the user if it is

correct– If the input is not correct, allow the user to

enter the data again


Slide 6- 215

Checking Input: get_int

• The get_int function seen in Display 6.7obtains an integer value from the user

– get_int prompts the user, reads the input, and displaysthe input

– After displaying the input, get_int asks the user to confirm the number and reads the user's responseusing a variable of type character

– The process is repeated until the user indicates witha 'Y' or 'y' that the number entered is correct


• The new_line function seen in Display 6.7 is called by the get_int function

– new_line reads all the characters remaining in the input line but does nothing with them, essentially discarding them

– new_line is used to discard what follows the first character of the the user's response to get_line's "Is that correct? (yes/no)"

• The newline character is discarded as well

Slide 6- 216

Display 6.7 (1)

Display 6.7 (2)

Checking Input: new_line


Slide 6- 217

Checking Input:Check for Yes or No?

• get_int continues to ask for a number until theuser responds 'Y' or 'y' using the do-while loop do {

// the loop body} while ((ans !='Y') &&(ans != 'y') )

• Why not use ((ans =='N') | | (ans == 'n') )?– User must enter a correct response to continue

a loop tested with ((ans =='N') | | (ans == 'n') )• What if they mis-typed "Bo" instead of "No"?

– User must enter a correct response to end the loop tested with ((ans !='Y') &&(ans != 'y') )


Slide 6- 218

Mixing cin >> and cin.get

• Be sure to deal with the '\n' that ends each input line if using cin >> and cin.get– "cin >>" reads up to the '\n'– The '\n' remains in the input stream– Using cin.get next will read the '\n'– The new_line function from Display 6.7 can

be used to clear the '\n'


Slide 6- 219

The Dialogue:Enter a number:21Now enter a letter:A

The Result:number = 21

symbol = '\n'

'\n' Example

• The Code: cout << "Enter a number:\n";int number;cin >> number;cout << "Now enter a letter:\n";char symbol;cin.get(symbol);


Slide 6- 220

A Fix To Remove '\n'

• cout << "Enter a number:\n";int number;cin >> number;cout << "Now enter a letter:\n";char symbol;cin >>symbol;


Slide 6- 221

Another '\n' Fix

• cout << "Enter a number:\n";int number;cin >> number;new_line( ); // From Display 6.7cout << "Now enter a letter:\n";char symbol;cin.get(symbol);


Slide 6- 222

Detecting the End of a File

• Member function eof detects the end of a file– Member function of every input-file stream– eof stands for end of file– eof returns a boolean value

• True when the end of the file has been reached• False when there is more data to read

– Normally used to determine when we are NOT at the end of the file

• Example: if ( ! in_stream.eof( ) )


Slide 6- 223

Using eof

• This loop reads each character, and writes it tothe screen

• in_stream.get(next);while (! in_stream.eof( ) )

{ cout << next; in_stream.get(next); }

• ( ! In_stream.eof( ) ) becomes false when the program reads past the last character in the file


Slide 6- 224

The End Of File Character

• End of a file is indicated by a special character

• in_stream.eof( ) is still true after the last character of data is read

• in_stream.eof( ) becomes false when the special end of file character is read


Slide 6- 225

How To Test End of File

• We have seen two methods– while ( in_stream >> next)– while ( ! in_stream.eof( ) )

• Which should be used?– In general, use eof when input is treated as text

and using a member function get to read input– In general, use the extraction operator method

when processing numeric data


• The program of Display 6.8…

– Reads every character of file cad.dat and copies it tofile cplusad.dat except that every 'C' is changed to"C++" in cplusad.dat

– Preserves line breaks in cad.dat• get is used for input as the extraction operator would skip

line breaks

• get is used to preserve spaces as well

– Uses eof to test for end of file

Slide 6- 226

Display 6.8 (1)

Display 6.8 (2)

Program Example:Editing a Text File


Slide 6- 227

Character Functions

• Several predefined functions exist to facilitate working with characters

• The cctype library is required– #include <cctype>

using namespace std;


Slide 6- 228

The toupper Function

• toupper returns the argument's upper case character – toupper('a') returns 'A'– toupper('A') return 'A'


Slide 6- 229

toupper Returns An int

• Characters are actually stored as an integer assigned to the character

• toupper and tolower actually return the integerrepresenting the character

– cout << toupper('a'); //prints the integer for 'A'

– char c = toupper('a'); //places the integer for 'A' in ccout << c; //prints 'A'

– cout << static_cast<char>(toupper('a')); //works too


• isspace returns true if the argument is whitespace– Whitespace is spaces, tabs, and newlines– isspace(' ') returns true– Example: if (isspace(next) )

cout << '-'; else

cout << next;– Prints a '-' if next contains a space, tab, or

newline character• See more character functions in

Slide 6- 230

Display 6.9 (1)

Display 6.9 (2)

The isspace Function


Slide 6- 231


• Can you– Write code that will read a line of text and echo

the line with all the uppercase letters deleted?

– Describe two methods to detect the end of an input file:

– Describe whitespace?

starting out with c++, 3 rd edition basic file operations in c++ dr. ahmed telba

Documents

c program

text file

file io

file inputoutput

file names

file access

rd edition writing

rd edition binary form