Files. Lecture 25

Outline

File handling in C - opening and closing.
Reading from and writing

Introduction

Data storages of computers
1- Main memory (RAM)
It is volatile
Read / Write

A file is a collection of related data that a computers

Text & Binary Files

How does computer store data?
They are coded
When data

Text Files

ASCII encoding
Each line is a string
Each line is

Binary Files

Binary encoding
int, double, float, struct, … are directly (as

Working with Files

Until now
We read/write data from/to terminal (console)
In C
We

Working with Files

Main steps in working with files
1) Open file
Get a

Opening Files

Function fopen opens files
#include
FILE * fopen(char *name, char

Opening Files: Modes

r: open for read. We cannot write to the

Opening Files: Modes

Files are
Text: Some strings
Binary: Image file, Video file,

Opening Files: Examples

FILE *fp;
fp = fopen("c:\test.txt", "r");
if(fp == NULL){
printf("Cannot open file\n");
return

More on fopen

File-Position pointer(FPP)

File-Position Pointer
A pointer in file
Points to current location of

More on File Open Modes

Closing Files

Each opened file should be closed.
If we write to a

Reading/Writing Text File

fscanf reads from file
fscanf is same to

Text File: Example

We have file in this format

#include
#include
int main(void){
FILE *fpin;
char inname[20];
int num, i, id;
float sum, average,

/* Read the number of students */
fscanf(fpin,"%d", &num);
/* Read the id

#include
#include
int main(void){
FILE *fpin, *fpout;
char inname[20], outname[20];
int num, i, id;
float

fclose(fpin);
fpin = fopen(inname, "r");
fscanf(fpin,"%d", &num);
fprintf(fpout, "%f\n", average);
for(i = 0; i <

Reading/Writing Characters (Text Files)

To write a character to file
fputc(char c, FILE

#include
#include
int main(void){
FILE *fpin, *fpout;
char inname[20], outname[20];
char c;
printf("Enter the name

Checking End of File

Each file has two indicators
End of file

Checking End of File

Previous example with feof
while(1){
c = fgetc(fpin);
if(feof(fpin))
break;
fputc(c, fpout);
}

#include
int main () {
FILE * pFile;
int n = 0;
pFile =

Read/Write a Line (Text File)

We can read a line of file

Read/Write a Line (Text File)

We can write a line to file

Example: Count the number of lines

char buf[500]; // 500 > every

#include
#include
int main(void){
FILE *fpin, *fpout;
char inname[20], outname[20];
char buf[1000];
printf("Enter the name

File 1:
3 30
1 2 3 4 5 6 7
12 34 56

void reverse_copy(FILE *fpin, FILE *fpout){
int lines, max_len, i = 0,

Binary Files: A Different File Format

Data in binary files are

No Conversion to ASCII

In text files, everything is saved as

Reading from Binary Files

int fread(void *buf, int size, int num,

Writing to Binary Files

int fwrite(void *buf, int size, int num,

fread: Examples

Reading 1 int from binary file fp
int i;
fread(&i, sizeof(int), 1,

fread: Examples

Read five floats
float farr[5];
fread(farr, sizeof(float), 5, fp);
This means
Read 5

fwrite: Examples

Writing 1 char to binary file fp
char c = 'A';
fwrite(&c,

fwrite: Examples

Writing 4 doubles to binary file fp
double darr[4];
fwrite(darr, sizeof(double),4,fp);
This means
Write

#include
struct point{
int x, y;
};
int main(void){
FILE *fp;
struct point p;
int i;
fp =

#include
struct point{
int x, y;
};
int main(void){
FILE *fp;
struct point p;
int i;
fp =

Sequential and Random Accesses

The access to file is sequential if

Random Access Files

Random access files
Access individual records without searching through

Moving FPP, Why?

To access randomly
Consider very large file (information about all

Moving FPP

int fseek(FILE *fp, long offset, int org)
Set FPP in the

fp = fopen("point.bin", "rb");
fread(&p, sizeof(p), 1, fp);
printf("%d %d\n", p.x, p.y);
fseek(fp, 2

Other FPP related functions

Find out where is the FPP
int ftell(FILE *fp)
ftell

#include
struct point{
int x, y;
};
int main(void){
FILE *fp;
struct point p;
int num;
fp =

fseek in Text files

Not very useful
Offset counts the number of