lab 11 input ouput files

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LECTURE 10

BITP 1113:

Files and Stream


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LEARNING OUTCOMES

At the end of this lecture, you should be able to:

1. Describe the fundamentals of input & output files.

2. Use data files for input & output purposes.


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Files

Normally, it is difficult to handle large amounts of inputdata and output data and would always be lost as soonas we turned off the computer .

We can use a file instead of keyboard for program input.The file is called input file.

We can use a file instead of monitor screen for programoutput. The file is called output file.

File a collection of related data usually stored insecondary storage devices such as Disk, Tape, etc.

Purpose to keep data in a secondary storage.


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Files

Using file, data can be created by one program, stored(or saved) on secondary devices, and then accessed ormodified by other programs when necessary.

Two major characteristics of files are:

Text files : data in text format Binary files : data in binary format

Files in a secondary storage can be both read andwritten. These processes are also known as input/output.


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Types of File Stream

The type of stream class determines if it is an input file or

an output file or both.

ofstream output file stream class. Creating files andwriting data to them (output file).

ifstream input file stream class. Opening existing

and reading data from them into memory (input file).

fstream file stream class. Creating files, writingdata to them and reading data from them (both input& output file).


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What are the steps needed to Use Files?

1) Include the header file

2) Define a file stream object using appropriate file streamclass

3) Open the file

4) Use the file

5) Close the file

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(1)- Include the header file

Standard input stream(cin) and standard output stream

(cout) requires the header file. File input/output stream both requires

header file.

(2) - Define a file stream object usingappropriate filestream class ( ifstream / ofstream / fstream )

A file is identified by its file name, e.g. student.dat

Inside a C++ program, a file is identified by a file stream

object.eg:ifstreaminFile; // inFile is an input file stream

// object, with ifstream class

eg:ofstreamoutFile;// outFile is an output file// stream object, with ofstream class

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Input / Output : File Name vs File Stream Object

inFile

outFile

student.dat

student_new.dat

ifstream inFile(student.dat);ofstream outFile(student_new.dat);

Memory


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File Name

Example:

ifstream myInputFile;char fileName[20];

cout> fileName;myInputFile.open(fileName);

OR

char fileName[20];

cout> fileName;

ifstream inFile(fileName);


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There are a few modes to open a file. They are listed asfollows:Mode Description

ios::in Input mode. Data will be read from the file. Thefile MUST exists. If the file doesnt exist, it will not be created

and the open function fails. ios::out Output mode. Data will be written to the file.

The file will be created if it does not exist. If it already exists,the files content will be deleted and replaced by the new data.

ios::trunc Truncate mode. Same as ios::out.

ios::appAppend mode. If the file already exists, itscontents are preserved and all output is written to the end of

the file. If the file doesnt exist, it will be created.

Open File Modes

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All these modes can be combined using the | operator(which means OR) .

For example, if we want to open the file example.binto add data we could do it by the following :

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

More on Open File Mode

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For all file stream classes, default mode/s is/areautomatically applied if the file is opened withoutspecifying any value for the mode parameter.

Stream class Default mode parameter

ofstream ios::out

ifstream ios::in

fstream ios::in | ios::out

More on Open File Mode

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(4) - Use the file

Can use output file stream object andto copy data

from file to variablesinFile >> partNum;inFile >> qtyInStock >> qtyOnOrder;

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(5) - Closing a File

When we are finished with our input and outputoperations on a file we should close it.

When a file is closed, any unsaved data in the buffer willbe saved to its file.

Closing a file improves systems performance (theoperating systems resources is better utilized.)

Use the close member function

inFile.close();

outFile.close(); After closing a file, the file stream object (above eg:inFile and outFile) can be used again to openanother file.


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Example of Output File

Writing output to a text file : Example 1

# include

# include using namespace std;

int main()

{

double income = 123.45, expenses = 987.65;

int week = 7, year = 2006;

ofstream outfile("L4_2.out");// default mode is ios::out

outfile


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Example of Output File: More on Example 1

Content of L4_2.out text file :

You can find the L4_2.out file in the same folder asthe C++ program that wrote the file. Open it using thenotepad.

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Writing output to a text file : Example 2

#include

#include

#include

using namespace std;

int main (){

char name[20];

char id[10];

float m1,m2;

ofstream dataFile (student.txt", ios::out);

cout> name >> m1 >> m2) //reading from keyboard using EOF while loop

{

dataFile


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Example of Output File : More on Example 2

For example the input of the program is entered asfollows :

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Example of Output File : More on Example 2

Content of student.txt text file :

You can find the student.txt file in the samefolder as the C++ program that wrote the file. Open itusing the notepad.

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Input files can be also created using any text editor.Notepad is an example of text editor you can use to saveyour data.

To create an input file using a text editor, open thenotepad and type the data. Save the file in the samefolder with the C++ program that will use these data.Example of the file is shown below:

Input Files

Save the file as : L4_3A.dat

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Reading data from a text file: Example 1# include # include #include


int main()

{

double x;

int i,j;

ifstream infile1("L4_3A.dat");ifstream infile2("L4_3B.dat");

infile1>>i>>j>>x;

infile1.close();cout


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Reading data from a text file: Example 2#include

#include

#include


int main ()

{ char line[50];ifstream myFile ("example.txt");

if (myFile.is_open()) //checking file existance

{ while (! myFile.eof() ) // checking EOF for myFile using while loop

{ myFile.getline (line,50); //read string from myFile

cout


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Reading data from a text file: Example 3#include

#include

#include


int main ()

{ char name[20];

char id[10];

float m1,m2;

ifstream dataFile (student.txt", ios::in);

if (!dataFile) // if dataFile exists, dataFile expression is TRUE

{

cout > id >> name >> m1 >> m2) //read from dataFile using EOF while loop

{

cout


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Example: Writing Data to a File#include

#include


voidmain()

{

ofstream myOutputFile; // declaring output file object

myOutputFile.open(student_new.dat); // file created in// the same directory as the program

myOutputFile


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Example: Reading Data From a File#include#include


voidmain(){ifstream myInputFile; // declaring input file objectchar name[50];

myInputFile.open(student_new.dat); // file will be// created in the same directory as the program

myInputFile >> name;cout name;cout name;cout


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#include #include #include //required to use exit()#include using namespace std;

voidmain(){char time[5];double temperature;

ifstream inFile("temperature.txt",ios::in);

ofstream outFile("temperature_revised.txt",ios::out);

if (!inFile) // check existence of input file{ cout >temperature;outFile


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Open the input file

ifstream inFile;

inFile.open(clients.txt",ios::in);OR

ifstream inFile(clients.txt",ios::in);

Open the output file

ofstream outFile;outFile.open("output.txt",ios::out);

OR

ofstream outFile("output.txt",ios::out);

Append the output file

ofstream outFile;outFile.open("output.txt",ios::app);

OR

ofstream outFile("output.txt",ios::app);


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Passing File Stream Objects to Functions#include#includeusing namespace std;

const int SIZE = 5; // maximum size of charactervoidshowContent (ifstream&); // function prototype

void main(){

ifstream inFile;

inFile.open("temperature.txt");

if ( !inFile){

cout


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voidshowContent (ifstream &inFileObj){

char time[SIZE];double temperature;

while (!inFileObj.eof()){

inFileObj >> time >> temperature; // read content

cout

lab 11 input ouput files

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