Chapter11_FileProcessing

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CSEB114: Principle of programming

Chapter 11: Data Files & File Processing



Objectives

prepared by NI, edited by MAF

In this chapter, you will learn about Files and streams

Creating a sequential access file

Reading data from a sequential access file

Using fgetc() and fputc() Using fgets() and fputs()

Using fprintf() and fscanf()

Using fopen() and fclose()



Files and Streams


C views a file as a sequential stream of bytes. A file ends either with an EOF (end-of-file) marker or

at a specified byte number specified by the system.

When a file is opened, a stream is associated with a

file. Streams provide communication channels between

files and the programs.

0 1 2 3 4 5 6 7 8 . . . . . n-1



Files and Streams


In addition to providing access to a file, a stream canalso be used to access devices.

For example, when a program (any program) isexecuted, 3 streams are automatically opened: standard input (stdin)

enable the program to read data from keyboard

standard output (stdout)

enable the program to print data on the screen

standard error (stderr)

enable program to print errors on the screen

They are all manipulated using file pointers.



Declaring a file


The standard library <stdio.h> provides some of thefile manipulation function.

Declaring file:FILE *the_file;

States that thefile is a pointer to a file structure

If there is more than one file, each file needs to have its

own FILE pointer.

thefile is an internal file name used by the program to

refer to the external file name (the actual physical file

stored on disk).



File operation: fopen ()


Before we can process a file, we must either open orcreate it.

Syntax for fopen( ):internal_file_name = fopen(external_file_name, OpenMode);

The fopen() function takes 2 arguments: the filename and the file mode.



File operation: fopen ()


Example:thefile = fopen(“my_file.txt”,”r”);

This statement will try to open a file called “my_file.txt”. my_file.txt is the external file name referring to a

phisycal file on the disk. If the file is to be placed in a different directory than the

program directory, the full path need to be specified.For example: “D:/my_file.txt”

The function returns a pointer to the successfullyopened file. But if the file cannot be opened, a NULL isreturned.



File OpenMode:


The following is the list of open mode that can be associated with

fopen( ).

“r” : to open existing file in input mode so data can be read from

it. The file to be opened must exist phisically on disk for this

open mode to be successful.

“w” : the file is intended to be an output file and we are planningto write data to it.

“a” : to append data to the end of existing file.

“r+” : to open existing file for update (both in input and output

mode). If the file already exist, the content is not destroy.

“w+” : destroy the file if already exist and open a new file for

update.

“a+” : open file for update (adding data at the end of the file.



fopen( )


You could also ask the users to specify the name ofthe file s/he want to open.

Example:

char filename[50];

printf("Enter file name: ");gets(filename);

thefile = fopen(filename,"r");

The users must enter the full filename, including the

extension (.txt, .doc etc) and path.



File operation: fail fopen( )


If fopen( ) is returning a NULL value, this means thatthe fopen( ) has failed.

This is due to any of the following reasons: Opening a non-existing file for reading

Opening a file for reading or writing without having granted theappropriate access to the file by the operating system.

Opening a file for writing when no disk space is available.

Therefore, in our program, we need to write

statements that would handle this failure.



fputc( )


fputc( ) is a function that would write a charactervalue to the file.

Syntax: Using character variable, ch:

fputc(ch, internal_file_name); Example:

char m = „c‟;

fputc(m, theFile);

Using character constant:

fputc(„a‟,internal_file_name);

Example

fputc(„c‟, theFile);



fputc() example


#include <stdio.h>

int main(void){

char ch;

FILE *thefile;

if ((thefile = fopen("file_putc.txt","w")) == NULL)

{

printf("File fail to open\n");

}

else

{

printf("Enter a character: ");

scanf("%c", &ch);

fputc(ch, thefile);}

fclose(thefile);

return 0;

}



fgetc( )


fgetc( ) is a function that would read a character froma file.

Syntax:

variable = fgetc(internal_file_name);

Where: variable is a character variable to hold the value returned

by fgetc( ).

Internal_file_name is the pointer to an open file.

Example:

char c;

fgetc(theFile);



fgetc( ): Example


#include <stdio.h>

int main(void){

char ch;

FILE *thefile;

if ((thefile = fopen("file_getc.txt","r")) == NULL)

{

printf("File fail to open\n");

}

else

{

ch = fgetc(thefile); /*read a character from the file */

printf("%c\n",ch);/* print the value of ch to the screen

*/}

fclose(thefile);

return 0;

}



fprintf( )


fprintf( ) is a function that would print values to the file

Syntax:fprintf(internal_name, variable expression);

Example 1:fprintf(theFile, “This is an example”);

Example 2:char name[50] = “Ahmad”

fprintf(theFile, name);

Example 3:char name[50] = “Ahmad”;

fprintf(theFile, “My name is” name);



fprintf( ): Example


#include<stdio.h>

int main(){

int i, power;

FILE *thefile;

if((thefile = fopen("file_fprintf.txt","w"))==NULL)

printf("File could not be open\n");

else{

for(i=1;i<=100;i++){

power=i*i;

fprintf(thefile,"%d\n",power);

}

printf("End of operations");

}fclose(thefile);

return 0;

}



fscanf( )


fscanf( ) is a function that read a value, or values ofmix data type from a file.

Syntax:

fscanf(internal_name,formatControl,

variableList);

Example:

char name[50];

int age;fscanf(theFile, “%s %d”, name, &age);



fscanf( ): Example


#include<stdio.h>

void main(){

int i, bil, matrik;

char grade[2];

char name[10];

FILE *thefile;

if((thefile = fopen("file_fscanf.txt","r")) == NULL)

printf("File could not be open");

else{

fscanf(thefile,"%d",&bil);

printf("%-10s%-10s%s\n","Matrik","Name","Grade");

for(i=0;i<bil;i++)

{fscanf(thefile,"%d%s%s",&matrik,name,&grade);

printf("%-10d%-10s%s\n",matrik,name,grade);

}

fclose(thefile);

}

}



fputs()


Writes the string to the file. The function begins outputting the string until it

reaches the terminating null character ('\0').

Syntax

fputs (string variable, internal name);

Example:

char str [20] = “gummy bear”;

fputs (str, theFile);



fputs( ): Example


#include<stdio.h>

int main(){

char str[20]= "let's picnic!";

FILE *thefile;

if((thefile = fopen("file_fputs.txt","w"))==NULL)


else

fputs(str, thefile);

fclose(thefile);

return 0;

}



fgets( )


fgets( ) read a string of characters from a file. Syntax:

fgets(stringVariable, size, internal_name);

Example:char content[50];

fgets(content, 50, theFile);

fgets( ) will readsize – 1

character from the filepointed by theFile, and saves the string into variable

content .



fgets( ): Example


#include<stdio.h>

int main(){

char str[30]= {'\0'};

FILE *thefile;

if((thefile = fopen("file_fgets.txt","r"))==NULL)


else{

fgets(str, 30, thefile);

puts(str);

}

fclose(thefile);

return 0;

}

Chapter11_FileProcessing

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