1. Files Operations

2. Introduction
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

3. 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

4. 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

5. File Mode Basics mode are: “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

6. Opening File and fopen function-example
FILE *in_file;
FILE *out_file;
in_file = fopen(“student.dat”, “r”);
out_file = fopen(“student.out”, “w”);

7. 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); }

8. 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); }

9. Closing File and fclose function
Each opened file need to be closed
Format:
fclose(internal_filename);
e.g
fclose(in_file);
fclose(out_file);

10. Check for End-of-File and the feof function
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)

11. 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);

12. Reading Data from Text Files
Format
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);

13. Writing Data to Text File
Format
fprintf(internal file name, format control string, output list);
fprintf(out_file, “%d”, marks);
fputc(character expression,internal file name);
fputc(ch, out_file);
fputc(“4”, out_file);
fputs(string expression, internal file name);
fputs(name, out_file);
fputs(“makan”, out_file);

14. Sample Program 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
#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); }

16. End Files Operation
Q & A!