Week 11 – Files
KUKUM Sem2-05/06
EKT120: Computer Programming
1
Introduction
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Almost all of the program developed before
this is interactive
In interactive environment, input is via
keyboard and output is via screen/monitor
This type of processing is not suitable if it
involves huge amount of input or output to
be entered or be displayed on the screen at
one time
Therefore, file processing can solve the
problem mentioned
KUKUM Sem2-05/06
EKT120: Computer Programming
2
File Declaration
To implement file processing in C
program, need to #include <stdio.h>
FILE *in_file;
FILE *out_file;
 in_file and out_file are known as
internal file name
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KUKUM Sem2-05/06
EKT120: Computer Programming
3
Opening File and fopen
function
Each file must be opened before it is processed
 While opening the file, external file name need to be
related to the internal file name using fopen
function.
 Format:
internal_filename =fopen(external_filename, mode);
 Internal file name is the name that the C system
uses to identify a file among others that a program
might process
 External file name is the name given at “save file as”
outside the program e.g. “student.dat”, “student.out”
etc
 Mode is used to open file
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KUKUM Sem2-05/06
EKT120: Computer Programming
4
File Mode
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Basics mode are:
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“r” : open file to read
“w” : open file to write
“a” : append data to the end of an already
existing file
“r+” : open and create file to update, i.e. read and
write; did not overwrite previous output
“w+” :open and create file for update; overwrite
“a+” : append; open or create file for update
KUKUM Sem2-05/06
EKT120: Computer Programming
5
Opening File and fopen
function-example
FILE *in_file;
FILE *out_file;
in_file = fopen(“student.dat”, “r”);
out_file = fopen(“student.out”, “w”);
KUKUM Sem2-05/06
EKT120: Computer Programming
6
File Open Verification
There is a possibility opening file fails.
 Maybe the particular file does not exist
 Therefore need to check or verify whether the
file is successfully opened
 If file fails to open, need to stop the program,
use exit(-1);
if (in_file == NULL)
{ printf(“File fails to open\n”);
exit(-1);
}

KUKUM Sem2-05/06
EKT120: Computer Programming
7
File Open Verification-cont

You can also combine open file and file
verification
if ((in_file = fopen(“student.dat”, “r”)) == NULL)
{
printf(“File fails to open\n”);
exit(-1);
}
KUKUM Sem2-05/06
EKT120: Computer Programming
8
Closing File and fclose function
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Each opened file need to be closed
Format:
fclose(internal_filename);
e.g
fclose(in_file);
fclose(out_file);
KUKUM Sem2-05/06
EKT120: Computer Programming
9
Check for End-of-File and the
feof function
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Usually you don’t know how many data
you want to read from file
Therefore, need to check whether you
have reach end of file
Format:
feof(internal_filename)
KUKUM Sem2-05/06
EKT120: Computer Programming
10
Check for End-of-File and the
feof function-example
FILE *in_file;
in_file = fopen(“student.dat”, “r”);
if(in_file == NULL)
{
printf(“Error opening file\n”);
exit(-1);
}
while(! feof(in_file))
{ //stmt to process data }
fclose(in_file);
KUKUM Sem2-05/06
EKT120: Computer Programming
11
Reading Data from Text Files
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Format
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fscanf(internal file name, format control string, input list);
fscanf(in_file, “%d”, &marks);
fgetc(internal file name);
ch = fgetc(in_file);
fgets(string variable, size, internal file name);
fgets(name, 10, in_file);
KUKUM Sem2-05/06
EKT120: Computer Programming
12
Writing Data to Text File
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Format
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fprintf(internal file name, format control string, output list);
fprintf(out_file, “%d”, marks);
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fputc(character expression,internal file name);
fputc(ch, out_file);
fputc(“4”, out_file);
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fputs(string expression, internal file name);
fputs(name, out_file);
fputs(“makan”, out_file);
KUKUM Sem2-05/06
EKT120: Computer Programming
13
Sample Program
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
FILE *in_file;
FILE *out_file;
int marks, total=0, count = 0;
float avg;
in_file = fopen("student.dat", "r");
out_file= fopen("student.out", "w");
if(in_file == NULL)
{
printf("Error opening file\n");
exit(-1);
}
KUKUM Sem2-05/06
while(!feof(in_file))
{
fscanf(in_file,"%d",&marks);
++count;
total = total + marks;
fprintf(out_file, " %d ",marks);
}
avg = total /count;
fprintf(out_file, "\n%.2f\n", avg);
fclose(in_file);
fclose(out_file);
return 0;
}//main
EKT120: Computer Programming
14
Sample input file and output
file
student.dat
50 60 70 80 90
44 55 66 77 88
24 56 79 50 77
student.out
50 60 70 80 90 44 55 66 77 88 24 56 79 50 77
64.00
KUKUM Sem2-05/06
EKT120: Computer Programming
15
End Week 10 – Files (1)
Q & A!
KUKUM Sem2-05/06
EKT120: Computer Programming
16