Data File Handlingg

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Data File Handlingin C++


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Introduction Computer programs are associated to work

with files as it helps in storing data &information permanently. File - itself a bunch of bytes stored on

some storage devices.

In C++ this is achieved through acomponent header file calledfstream.h The I/O library manages two aspects- as

interface and for transfer of data. The library predefine a set of operations

for all file related handling through certainclasses.


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C++ provides a new technique for handlingI/O operations through mechanism known as

streams.

A stream refers to a flow of data.

Classified in 2 categories:

1. Output stream

2. Input stream

In output stream flow of data is from program to

the output device.In input stream the flow of data is from input

device to a program in main memory.


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Thefstream.hheader file

Streams act as an interface between files andprograms.

They represent as a sequence of bytes and deals withthe flow of data.

Every stream is associated with a class having memberfunctions and operations for a particular kind of data

flow.

File Program ( Input stream) - readsProgram File (Output stream) write

All designed into fstream.h and hence needs to beincluded in all file handling programs.

Diagrammatically as shown in next slide


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Stream Class Hierarchy

ios

ostreamistream

fstream

iostream

ofstreamifstream

User-Defined

Streams

System-Defined

Streams


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Why to use Files:Convenient way to deal large quantities of data.

Store data permanently (until file is deleted).

Avoid typing data into program multiple times.

Share data between programs.

We need to know:

how to "connect" file to program

how to tell the program to read datahow to tell the program to write data

error checking and handling EOF


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Stream Insertion Operators (data write) Are defined in the ostream class

The operator , called the extractor, accepts any built-

in data type passed as arguments


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1: To access file handling routines:

#include

2: To declare variables that can be used to access file:ifstream in_stream;

ofstream out_stream;

3: To connect your program's variable (its internal name)

to an external file (i.e., on the Unix file system):in_stream.open("infile.dat");

out_stream.open("outfile.dat");

4: To see if the file opened successfully:

if (in_stream.fail())

{ cout


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5: To get data from a file (one option), must declare

a variable to hold the data and then read it using

the extractionoperator:

int num;

in_stream >> num;

6: To put data into a file, use insertion operator:out_stream


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Example (creating file)

#include

#include

#include

int main()

{

ofstream input;

input.open ("stu.txt");

input


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Example (creating file)

#include

#include

Void main()

{

int rollno

char name[10];

ofstream ofil(stud.txt);

coutrollno>>name;

cout


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Reading a file

#include

#include

Void main()

{

int rollnochar name[10];

Ifstream ifil(stud.txt);

If(!ifil) //if( ifil.fail() )

{

Cout


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coutrollno>>name;

cout


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ios:: app - (append) write all output to the end of file

ios:: ate - data can be written anywhere in the file ios:: binary - read/write data in binary format

ios:: in - (input) open a file for input

ios::out - (output) open a file for output

ios:: trunc -(truncate) discard the files contents if itexists

File Open Modes


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Stream state member functions

In C++, file stream classes inherit a stream statemember from the ios class, which gives out the

information regarding the status of the stream.

For e.g.:

eof()used to check the end of file character

fail()- used to check the status of file at openingfor I/O

bad()- used to check whether invalid fileoperations or unrecoverable error .

good()- used to check whether the previous fileoperation has been successful


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File Input and Output Using Objects

Example:

#include

class student

{

private:

int iReg_no;

char name[20];

public:

void setRegno()

{CoutiReg_no;

}


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void setName()

{

Coutname;

}

int getRegno()

{

Cout


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void main()

{

ofstream Sfil(studfile.dat);char ch;

student Svar;

Svar.setRegno();

Svar.setName();

Sfil


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cout>ch;

if(ch== y)

{

ifstream Sfil(studfile.dat);

char ireg;char nam[20];

Sfil>>ireg>>nam;

cout


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// Initial experience reading and writing files#include #include #include

int main(){ ifstream in_stream;ofstream out_stream;int num;in_stream.open("numbers.dat");if (in_stream.fail()) { cout


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INPUT AND OUTPUT OPERATION

put() and get() functionthe function put() writes a single character to theassociated stream. Similarly, the function get() reads asingle character form the associated stream.example :file.get(ch);file.put(ch);

write() and read() functionwrite() and read() functions write and read blocks of data.example:file.read((char *)&obj, sizeof(obj));file.write((char *)&obj, sizeof(obj));


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int main()

{

ifstream mys;

char c;

mys.open("new.txt");

if(mys.fail())

{

cout


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while (!mys.eof())

{

cout


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class Person

{

private:char name[40];

int age;

public:

void getData()

{

cout > name;

cout > age;

}} ;


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int main()

{

Person per ;

per.getData();

ofstream outfile("Person.txt");

outfile.write((char*)&per, sizeof(per));

return 0;

getch();}


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struct record

{

char player[20];int age;

int runs;

}emp;

void add()

{

ofstream fp("jk.txt",ios::out);


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if(!fp)

{

coutemp.age>>emp.runs;

fp.write((char *)&emp,sizeof(emp));fp.close();

}

void display()


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void display()

{

ifstream fp("jk.txt",ios::in);

if(!fp)

{

printf("file cannot be opened");

exit(1);

}

printf("records entered");

fp.read((char *)&emp,sizeof(emp));

cout


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deletionvoid del()

{ int r;

student obj;

ifstream fp1;

ofstream fp2,fp3;fp1.open("student.dat",ios::in);

fp2.open("temp1.txt",ios::app);

fp3.open("temp2.dat",ios::app);

puts("Enter the deleting roll no.");

cin>>r;


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while(fp1.read((char *)&obj,sizeof(obj)))

{

if(r==obj.roll())

{

fp2.write((char *)&obj,sizeof(obj));

}

else

{


}

}remove("student.txt");

rename("temp2.txt","student.txt");

getch();}

updating


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updatingvoid update()

{

student obj;

int r;

ifstream fp1;fp1.open("student.txt");

ofstream fp2;

fp2.open("temp.txt",ios::app);

puts("Enter the rollno. to be modified");

cin>>r;


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while(fp1.read((char*)&obj,sizeof(obj)))

{

if(obj.roll()==r)

{puts("Enter new roll no. and name");

obj.getdata();

fp2.write((char*)&obj,sizeof(obj));

}

else

{


}

}remove("student.txt");

rename("temp.txt","student.txt");

getch();

}


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File pointers

The get Pointer

Specifies the location in the file where thenext read operation will occur


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The put Pointer

Specifies the location in the file where the

next write operation will occur


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The seekg() Function

Helps to control the get pointer

Moves the get pointer to an absoluteaddress within the file or to a certain number

of bytes from a particular position

Takes two arguments:The number of bytes to move

The reference in the file from where the pointer

has to be repositioned

Example:

ifstream iFil;

iFil.seekg(10,ios::beg);


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The tellg() Function

Helps to control the get pointer

Can be used to find the current position of

the get file pointer in a file

Does not take any arguments

Example:

int iPosition=iFil.tellg();


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The seekp() Function

Helps to control the put pointer

Moves the put pointer to an absolute

address within the file or to a certain number

of bytes from a particular position


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The tellp() Function

Helps to control the put pointer

Can be used to find the current position of

the put file pointer in a file


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ExampleTo find the size of the file

#include

#include

Void main()

{

Ifstream ifil(abc.txt);

If(!ifill)

{

Cout


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ifill.seekg(0,ios::end);

int x=ifil.tellg();

Cout


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void student::getdata()

{

coutname;

coutrollno;

}

void student::date::getdate()

{

cout


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void student::display()

{

cout


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cout

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