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Files

Computer Programming and Utilization

Prof. Munindra Lunagaria

MEFGI, India

Files

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A file is nothing but a collection of records and each line of the data is recorded in

the file.

The record is a group of related data items.

The library functions to access the files are available in stdio.h

Introduction

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The reading and writing of data is done with streams.

A stream is a file and using physical device like keyboard information is stored inthe file.

Printer and monitor are used to display the stream.

The FILE object uses these devices.

The FILE object contains all the information about a stream like current position,pointer to any buffer, error and end of file (EOF).

Streams and File Types

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Sequential File: Here, data are arranged sequentially.

To read the last record of the file it is expected to read all the

records before it.

It takes more time to access the records.

Random Access File: In this type, data can be read and

modified randomly without reading the intermediate

records.

File Types

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Opening a File

Opening of file creates a link between operating system and file

functions

FILE *fp;fp=fopen(data.txt,r);

fopen()performs following tasks:

Searches the disk for opening of file

If file exists, loads the file from disk to memory

If file does not exist, returns NULL

Locates a character pointer pointing to first character of file

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Reading or Writing a File

The fgetc() function is used to read the contents of the file

ch=fgetc(fp);

The fputc()function is used to write the contents in the file.ch=fputc(c,fp);

It reads and write the character from and in the current pointerposition and advances the pointer position so that the next character is

pointed.

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Closing the file enables to wash out all its contents from

RAM buffer, and further link is disconnected from the file.

To close a single file:

fclose(fp);

To close all opened files

fcloseall();

It returns the number of files that have been closed.

Closing a File

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Write a Program on Opening and Closing the File

# include

# include # include

void main()

{

FILE *fp;

char c= ;

clrscr();

fp=fopen(data.txt,w);

if(fp==NULL)

{

printf(Can not open file);

exit(1);}

printf(Write data & to stop

press .:);

while(c!=.){

c=getche();

fputc(c,fp);

}

fclose(fp);

printf(\n Contents read :);fp=fopen(data.txt,r);

while(!feof(fp))

printf(%c,getc(fp));

}

OUTPUT :

Write data & to stop press .:

ABCDEFGHIJK.

Contents read: ABCDEFGHIJK.

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Text Modes

w (write)Opens a new file for writing

r (read)If file is found, loaded to memory; if not, returns NULL

a (append)

Opens a pre-existing file for appending dataw+ (write + read)

If file is found, its contents are destroyed; if not, new file is created

a+ (append + read)

Contents of file can be read and records can be added at the end offile

r+ (read + write)Read and write the record in file

Write a Program to Open a Pre existing Fi e an A

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Write a Program to Open a Pre-existing Fi e an A

Information at the End of File. Display the Contents of

the File Before and After Appending.

# include

# include

# include void main()

{

FILE *fp;

char c;

clrscr();printf(Contents of fi le before appending :\n);

fp=fopen(data.txt,r);

while(!feof(fp))

{

c=fgetc(fp);

printf(%c,c);

}

fp=fopen(data.txt,a);

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Continueif(fp==NULL)

{

printf(File can not appended);

exit(1);

}

printf(\n Enter string to append :);

while(c!=.)

{

c=getche();

fputc(c,fp);}

fclose(fp);

printf(\n Contents of file After

appending :\n);

fp=fopen(data.txt,r);

while(!feof(fp)){

c=fgetc(fp);

printf(%c,c);

}

}

OUTPUT :

Contents of file before appending:

String is terminated with \0.

Enter string to append :

This character is called as NULL

character.

Contents of file After appending:

String is terminated with \0.

This character is called as NULL

character

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wb (write)Opens a binary file in write mode

rb (read)Opens a binary file in read mode

ab (append)Opens a binary file in append mode

r+b (read + write)Opens a pre-existing file in read and write mode

w+b (read + write)Creates a new file in read and write mode

a+b (append + write)Opens a file in append mode. If file does not exist, new file is created

Binary Modes

P t U + M d f W iti d R di f

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Program to Use w+ Mode for Writing and Reading of a

File

# include

# include

# include void main()

{

FILE *fp;

char c= ;

clrscr();

fp=fopen(data.txt,w+);if(fp==NULL)

{

printf(Can not open file);

exit(1);

}

}

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printf(Write data & to stop press . :);

while(c!= .)

{

c=getche();

fputc(c,fp);

}rewind(fp);

printf(\n Contents read :);

while(!feof(fp))

printf(%c,getc

(fp));}

OUTPUT :

Write data & to stop press .: ABCDEFGHIJK.

Contents read : ABCDEFGHIJK.

Continue

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fprintf(): writes contents to the file

fscanf(): reads contents from the file pointed by file pointer

getc(): reads a single character from opened file and moves the file pointer

putc(): writes a single character into a file

fgetc(): reads a character and increments pointer

fputc(): writes the character to file

fgets(): reads string from a file

fputs(): writes string to a file

putw(): writes an integer value to the file

getw(): returns the integer value from a file

FileI/O

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# include

# include

void main(){

FILE *fp;

char text[15]; OUTPUT:

int age; Name AGE

fp=fopen(Text.txt,w+); AMIT 12

clrscr(); Name AGE

printf(NametAGE\n); AMIT 12

printf(Name\t AGE\n );

scanf(%s %d,text,&age);

fprintf(fp,%s %d, text,age);

printf(Name\t AGE\n );fscanf(fp,%s %d,text,&age);

printf(%s\t%d\n, text,age);

fclose(fp);

}

A Simple Program to Demonstrate the Use of fscanf() and fprintf().

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fseek(): This function is used to seek the file pointer at specified

position.

fseek(filepointer,offset,position);

Position can be

SEEK_SETSEEK_CUR

SEEK_END

ftell(): This function is used to tell the current position of file

pointer.

P=ftell(filepointer);

Other File Operation

W it P t R d th L t F Ch t

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# include

# include

# include

void main()

{

FILE *fp;

int n,ch;

clrscr();

fp=fopen(text.txt,r);

printf(\nContents of fi le\n);

while((ch=fgetc(fp))!=EOF)

printf(%c,ch);

printf(\n Howr many characters including spaces would you like

to skip ? :);

scanf(%d,&n);

Write a Program to Read the Last Few Charactersof the Fiile Using the fseek()Statement

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fseek(fp,-n-2,SEEK_END);

printf(\nLast %d characters of a fi le\n,-n-2);

while((ch=fgetc(fp))!=EOF)

printf(%c,ch);

fclose(fp);

}

OUTPUT:

How many characters including spaces would you like to

skip? : 4

Last 5 characters of a file

WORLD

Continue

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