c-programming-class 7

8/14/2019 C-Programming-Class 7

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Session 07

File Handling in C


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Session Objectives

To know how to create and handle files.

To be able to differentiate between various

types of files. To be in a position to write involved

programs like inventory control, record

handling in files etc.,


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Session Topics

File the structured data type

Temporary and permanent file

Organization of file

File operation


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Files

Files are helpful in providing permanent storage ofinput/output that can be accessed at any point oftime later.

A file is a region of memory space in the storagemedia and it can be accessed using the libraryfunctions available in stdio.h or by the systemcalls of the operating system.

File contains bytes of information.

NOTE:It is not a data type.


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Classification of Files

The files which are

accessed by using library

functions are known as

High Level Files.

These files areportable as

they make use of library

functions common to all

operating systems.

Stream oriented files.

The files which areaccessed by using systemcalls of the operating

system are known asLowLevel Files.

These files make use ofthe system calls of theoperating system under

which the program is run. System oriented files.

High Level Files Low Level Files


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Streams

A stream is a source of data or destination of data that may

be associated with a disk or other I/O devices.

The source stream provides data to a program and it is

known as an input stream.

The destination stream receives the output from the

program and is known as output stream.

A stream is a pointer to a buffer of memory which is used

for transferring the data.


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Types of I/O Streams

It is a sequence of

lines of text.

A file created using a

text stream is called as

a Text File.

It is a sequence of

unprocessed bytes.

A file created using a

binary stream is called

as a Binary File.

Text Stream Binary Stream


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FILE & File Pointer

FILE is a structure defined in stdio.h and also it ispredefined data type using typedef.

The pointer to a FILE data type is called as a FilePointer.

A file pointer points to the block of information ofthe stream that has just been opened.


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Why File Handling?

It is a very difficult to input large volume of data

through terminals and apart from this, it is time

consuming to enter such large volume of datausing keyboard.

If the program is terminated for any of the

reason or computer is turned off, the entire input

data is lost.


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File Operations

The various file operations that are

performed are:

Open a fileRead data from the file

Write data into the file

Closing a file


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1. Opened for read, write and append

2. File pointer is at the end of file

appenda+

1. Opened for read and write and the file contents

are lost if file exists.

2. If file does not exist, the file is read write and

file pointer points to beginning of file.

read writew+

Opening for read and write and the file pointer points

to the beginning of file.

read writer+

1. If the file already exists, file pointer is set to

end of file in write mode.2. If the file does not exists, it is created for

writing and file pointer is at the beginning.

appendA

1. If the file already exists, the contents are lost.

2. If file does not exist, a file is created for

writing.

write onlyW

File pointer is set to beginning if fileread onlyR

DescriptionMeaningMode

File Operating Modes


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The file should be opened before reading a file or before writing into a file.

Syntax:fp = fopen(char *filename,char *mode)

where

-fp is a file pointer of type FILE

-filename holds the name of the file to be opened.Thefilename should be avalid identifier.

- mode details

Return Values:

- file pointer if successful

- NULL if unsuccessful

Example:

FILE *fp1,*fp2;

fp1=fopen(file_1,r);

fp2=fopen(file_2,w)

fopen()


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This function is used to close the opened file. A file should be closed

when all file operations are over.

This ensures that all buffers are flushed and all the links to the file

are broken.

Syntax:

int fclose(FILE *fp)fp is a file pointer

Return Values:- 0 if successful

- EOF on error Example:

fclose(fp1);

fclose(fp2);

fclose()


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#include

#define NULL 0

void main()

{

FILE *fp;

fp = fopen(sample.dat,r+);

if(fp = NULL)

printf(\n Error!Cannot open the file);

else

{

..;

fclose(fp);

}

}

File Handling:An Example


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Syntax:

fscanf(fp,control string,list);

- fp is a file pointer

- the variables specified in the listwill take values from thefile specifed by fp using the specifications provided in

control string.

Example:

fscanf(fp,%d %s %f,&id,name,&salary);This function returns the number of items that are

successfully read from the file identified by file pointerfp.

fscanf()


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Syntax:

fprintf(fp,Control string,list);


- the values of the variables specified in the listwill bewritten into the file identified by fp using the

specifications provided in control string.

Example:

fprintf(fp,%d %s %f,id,name,salary);This function returns the number of items that are

successfully written into the file identified by file pointer

fp.

fprintf()


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Error Handling

During I/O operations, the following errors may occur

2. Reading beyond end of file marker

3. Unable to open a file

4. Invalid file name

5. Attempting to write to a write-protected file

feof()- This function is used to check for end of file.

- This function accepts the file pointer as a parameter.

Return values:

- If end of file is detected, a non zero value is returned.

- If end of file is not detected, zero is returned.

Example: If fp points to EOF

if(feof(fp))

printf(End of file is reached\n);


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This macro is used to get the status of file.

This function accepts the file pointer as a parameter.

Return values:

-If error is detected, a non zero value is returned.

- If error is not detected, zero is returned.

Example: If fp is a file pointer

if(ferror(fp)!= 0)

printf(Error in the file \n);

ferror()


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Program which provides error handling in files

void main(){

FILE *fp;

int i;

char file_name[10];

char ch;

printf(Enter the file name\n);

scanf(%s,file_name);

fp = fopen(file_name,r);

if(fp == NULL){

printf(Not successful\n);

exit(0);}

for(i=0;i


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File Control Functions

ftell()This function is used to obtain the current position of the file pointer.

Syntax:

long ftell(FILE *fp);

Return Values:

- Returns the current position of the file pointer, on success

- Returns EOF on error.

Example:

If this function returns 1000, it indicates 999 characters have been read

so far from the file and the file pointer fp is pointing to the 1000th

character in the file.


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This function is used to reposition the file pointer i.e, it is used to move the

file pointer to the desired position within the file.Syntax:

int fseek(FILE *fp,long offset, int start_point);


- offset can take positive,negative or zero value and specify the number ofbytes to be moved from the location specified by start_point.

- start_point an take one of the values.

0 indicates beginning of file.

1 indicates from the current position.

2 indicates from the end of file.

Return Values:

If success, returns 0.

Unsuccessful, returns non zero value.

Example:

fseek(fp,0,0 ) file pointer moves to the beginning of file

fseek()


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This function accepts file pointer as a parameter and resets the

position of the file pointer to the start of the file.

Syntax:

rewind(file pointer);Example:

If file pointer fp is in position 1000, by executing this

function, the file pointer fp is set to the very first position in

the file.

rewind()


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Summary

Files are helpful in providing permanent storage ofinput/output that can be accessed at any point of timelater.

A stream is a source of data or destination of data that maybe associated with a disk or other I/O devices.

FILE is a structure defined in stdio.h and also it ispredefined data type using typedef.

The pointer to a FILE data type is called as a File Pointer.A file pointer points to the block of information of thestream that has just been opened.


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