chapter 8 file operation

8/22/2019 Chapter 8 File Operation

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Chapter 8 : File Operation

1

Chapter 8

File Operation


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Objectives

Understand the files input and outputoperation

Capable to use and manipulate filesoperation


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Files

In C, file is used to store informationpermanently on a hard disk.

The data in file still hold the informationeven the computer is off.

C provides a set of library function forcreating and processing information

stored in data files. Files created can be read by any text

mode editor such as notepad.


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Files

There are four operations in files:

Open/Create file

Writing to file

Reading from file

Close file

First, the file must be open before anyoperation can be perform.


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Opening Files

Before read information from or writeinformation to file, an area of memorycalled buffermust be created.

Bufferstore information temporarilywhen reading from hard disk or writinginformation from memory to hard disk.

Buffer is created using: FILE *input


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File Declaration

Use stdio.h library

Format :

FILE *input;FILE will create buffer area.

input is a file pointer that point tothe location of data in buffer area.


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Opening & Closing Function

Use fopen()function to open files

Format :

FILE *input;input = fopen(filename,access);

Use fclose()function to close it

Format :fclose(input);


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Access

Opens file for update (read the entire

file, or write to the end of it)

a+

Open a new file for reading andwriting

w+

Opens file for update (read & write)r+

Opens file for appending (adding toit)

aOpens a new file for writing (Create)

w

Opens file for readingr

DecriptionMode


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9Outline Program for Opening &Closing File

#include

FILE *input;

input = fopen(Test.txt,w);.

.

fclose(input);


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Example Create & Write to file

#include

main()

{

FILE *input; /*declare a file*/

input = fopen(test.txt, w); /*create the file*/fprintf(input, Welcome to the world!); /* write to

the file*/

fclose(input);/*close the file*/

}

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Writing to a File

Must open in write, add or update accessmode

To write to a file, use fprintf() function.

The statement:fprintf(input, Welcome to

the world!); writes the output to file

pointed by input.

Note that the file pointerinputappears as

the first argument in the argument list.

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Exercise

Create a file name result.txt

and write the following datausing forcontrol statement.

0 1 2 3 4 5 6 7 8 9

Ch t 8 Fil O ti


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Reading from a File

To read data from file, it must be openedin read or update access mode.

fopen(text.dat, r);

To read from a file, use fscanf()

function.

Check the end-of-file by using the EOF.



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Example Read a file

#include

main()

{

FILE *input; /*declare a file*/

input = fopen(test.txt, r); /*read the file*/char str[20];/*declare a string*/

fscanf(input, %s,str); /* write to

the file*/

printf(%s,str); /*display to the screen the data*/

fclose(input);/*close the file*/

}



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FEOF

if (!feof(input))

{

fscanf(input,"%d",&num);}



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Exercise

Read a file name result.txt

And display its content onscreen



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File Open Verification

Under certain circumstances, an attemptto open a file may fail file may not exist.

In this case fopenfunction is fail and the

program cannot execute properly.

Good programming practice to verify thesuccess offopenand terminate the

execution in case of failure. Iffopenfunction call returns a NULL, then

the call is failed.



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File Open Verification

A program execution may terminate by using theexitfunction declared in stdl ib.hheader file.

The exit function has one integer argument,

which is returned to the operating system uponprogram termination: ex it (-1)

In common practice a negative value is taken asindication of abnormal program termination.



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19Example#include

#include

#include

void main()

{

FILE *input; /*declare a file */

char file_name[15];

printf("\nEnter the file name to open: ");

gets(file_name);

if ((input=fopen(file_name, "r")) ==NULL ){

printf("Cannot open file name %s", file_name);

getch();

exit(-1);

}



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20ExerciseWrite a function name open_file that read a filename result.txt and display its content on screen.

Put the file verification in your function. The mainprogram is provided as below:

void main()

{

char file_name[15];void open_file(char *);

printf("\nEnter the file name to open: ");

gets(file_name);

open_file(file_name);

getch();

}

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