1.11 File Handling in C Programming

Module 1.11 • Persistent Storage, I/O Streams, Binary Records & Random Access

1.11.1 Introduction to File Handling

So far, most programs store data in variables and arrays. The problem is:

Data remains only while the program runs.
When the program terminates, data is lost.

To store data permanently, C provides File Handling. A file allows data to be:

Saved permanently
Retrieved later
Modified when required
Shared between programs

Real-Life Examples

Student Records
Employee Databases
Banking Applications
Inventory Systems
Hospital Management Systems

1.11.2 What is a File?

A file is a collection of related data stored on secondary storage devices such as:

Hard Disk
SSD
USB Drive
Memory Card

Example:

Employee Records
 
1001  Ravi   45000
1002  Meera  52000
1003  Arjun  61000

1.11.3 Advantages of File Handling

Permanent Storage

Data remains even after program termination.

Large Data Storage

Files can store much larger data than variables.

Data Sharing

Multiple programs can access the same file.

Easy Data Management

Records can be added, modified, searched, and deleted.

1.11.4 Types of Files in C

C supports two major file formats:

Text Files

Data is stored as characters.

Example:

Ravi 25
Meera 30

File extension:

.txt
.dat
.csv

Binary Files

Data is stored exactly as it exists in memory.

Example:

1010100010110010

Not human-readable. Common extensions:

.bin
.dat

1.11.5 Text File vs Binary File

Feature	Text File	Binary File
Readability	Human readable	Not readable
Speed	Slower	Faster
Storage	More space	Less space
Portability	High	Medium
Editing	Text editor	Special programs

1.11.6 File Processing Steps

Every file operation follows three steps:

Open File
    ↓
Read / Write
    ↓
Close File

1.11.7 FILE Pointer

C uses a special pointer called FILE pointer.

Declaration

FILE *fp;

This pointer connects the program and file.

1.11.8 Opening a File

The function used is: fopen()

Syntax

FILE *fp;
 
fp = fopen("employees.txt","r");

1.11.9 fopen() Syntax

fopen(filename, mode);

Example:

FILE *fp;
 
fp = fopen("sales.txt","w");

1.11.10 File Opening Modes

Mode	Description
r	Read
w	Write
a	Append
r+	Read + Write
w+	Write + Read
a+	Append + Read

1.11.11 Read Mode

fp = fopen("records.txt","r");

Requirements:

File must already exist.

Purpose:

Read data only.

1.11.12 Write Mode

fp = fopen("records.txt","w");

Purpose:

Create file
Write data

Important: Existing contents are erased.

1.11.13 Append Mode

fp = fopen("records.txt","a");

Purpose:

Add data at end of file.

Existing data remains unchanged.

1.11.14 Checking File Open Errors

Always verify whether file opened successfully.

Example

#include<stdio.h>
 
int main()
{
    FILE *fp;
 
    fp = fopen("report.txt","r");
 
    if(fp == NULL)
    {
        printf("File cannot be opened");
        return 1;
    }
 
    fclose(fp);
 
    return 0;
}

1.11.15 Closing a File

Use: fclose()

Syntax

fclose(fp);

Benefits:

Saves pending data
Releases memory
Prevents file corruption

1.11.16 Writing Characters to a File

Function: fputc()

Example

#include<stdio.h>
 
int main()
{
    FILE *fp;
 
    fp = fopen("letters.txt","w");
 
    fputc('X',fp);
    fputc('Y',fp);
    fputc('Z',fp);
 
    fclose(fp);
 
    return 0;
}

File Content:

XYZ

1.11.17 Reading Characters from a File

Function: fgetc()

Example

#include<stdio.h>
 
int main()
{
    FILE *fp;
    char ch;
 
    fp = fopen("letters.txt","r");
 
    while((ch=fgetc(fp))!=EOF)
    {
        printf("%c",ch);
    }
 
    fclose(fp);
 
    return 0;
}

Output:

XYZ

1.11.18 Character Copy Program

#include<stdio.h>
 
int main()
{
    FILE *src,*dest;
    char ch;
 
    src=fopen("input.txt","r");
    dest=fopen("output.txt","w");
 
    while((ch=fgetc(src))!=EOF)
    {
        fputc(ch,dest);
    }
 
    fclose(src);
    fclose(dest);
 
    return 0;
}

1.11.19 Writing Strings

Function: fputs()

Example

FILE *fp;
 
fp=fopen("message.txt","w");
 
fputs("Welcome to Coding Hub",fp);
 
fclose(fp);

1.11.20 Reading Strings

Function: fgets()

Example

char text[100];
 
fgets(text,100,fp);

1.11.21 String File Example

#include<stdio.h>
 
int main()
{
    FILE *fp;
    char line[100];
 
    fp=fopen("message.txt","r");
 
    fgets(line,100,fp);
 
    printf("%s",line);
 
    fclose(fp);
 
    return 0;
}

Output:

Welcome to Coding Hub

1.11.22 Formatted File Output

Function: fprintf(). Works like printf().

Example

#include<stdio.h>
 
int main()
{
    FILE *fp;
 
    fp=fopen("staff.txt","w");
 
    fprintf(fp,
            "ID=%d Salary=%.2f",
            501,
            48500.75);
 
    fclose(fp);
 
    return 0;
}

1.11.23 Formatted File Input

Function: fscanf(). Works like scanf().

Example

int id;
float salary;
 
fscanf(fp, "%d %f", &id, &salary);

1.11.24 Employee Record Example

#include<stdio.h>
 
int main()
{
    FILE *fp;
 
    char name[20];
    int age;
 
    fp=fopen("employee.txt","w");
 
    fprintf(fp, "Karan %d", 29);
 
    fclose(fp);
 
    fp=fopen("employee.txt","r");
 
    fscanf(fp, "%s%d", name, &age);
 
    printf("%s %d", name, age);
 
    fclose(fp);
 
    return 0;
}

Output:

Karan 29

1.11.25 Writing Structures to File

Consider:

struct Product
{
    int id;
    float price;
};

Write structure:

fwrite(&item, sizeof(item), 1, fp);

1.11.26 Reading Structures from File

fread(&item, sizeof(item), 1, fp);

1.11.27 Binary File Example

#include<stdio.h>
 
struct Product
{
    int id;
    float price;
};
 
int main()
{
    FILE *fp;
 
    struct Product p =
    {
        101,
        899.50
    };
 
    fp=fopen("products.dat","wb");
 
    fwrite(&p, sizeof(p), 1, fp);
 
    fclose(fp);
 
    return 0;
}

1.11.28 Reading Binary Records

#include<stdio.h>
 
struct Product
{
    int id;
    float price;
};
 
int main()
{
    FILE *fp;
 
    struct Product p;
 
    fp=fopen("products.dat","rb");
 
    fread(&p, sizeof(p), 1, fp);
 
    printf("%d %.2f", p.id, p.price);
 
    fclose(fp);
 
    return 0;
}

Output:

101 899.50

1.11.29 Random File Access

Normally files are accessed sequentially. Random access allows direct movement to any location.

Functions used:

fseek()
ftell()
rewind()

1.11.30 fseek()

Moves file pointer.

Syntax

fseek(fp, offset, position);

1.11.31 Example of fseek()

fseek(fp, 20, SEEK_SET);

Meaning: Move 20 bytes from beginning.

1.11.32 ftell()

Returns current position.

Example

long pos;
 
pos = ftell(fp);
 
printf("%ld",pos);

1.11.33 rewind()

Moves pointer to beginning.

Example

rewind(fp);

Equivalent to:

fseek(fp,0,SEEK_SET);

1.11.34 File Position Example

FILE *fp;
 
fp=fopen("data.txt","r");
 
printf("%ld\n",ftell(fp));
 
fseek(fp,15,SEEK_SET);
 
printf("%ld\n",ftell(fp));
 
rewind(fp);
 
printf("%ld\n",ftell(fp));

Output:

0
15
0

1.11.35 End of File Detection

EOF means: End Of File. Used while reading files.

Example

while((ch=fgetc(fp))!=EOF)
{
    printf("%c",ch);
}

1.11.36 feof()

Checks whether end of file reached.

Example

if(feof(fp))
{
    printf("End of File");
}

1.11.37 ferror()

Checks file errors.

Example

if(ferror(fp))
{
    printf("File Error");
}

1.11.38 clearerr()

Clears file error indicators.

Example

clearerr(fp);

1.11.39 fflush()

Forces buffered data to be written immediately.

Example

fflush(fp);

1.11.40 rename()

Renames files.

Example

rename("oldreport.txt", "newreport.txt");

1.11.41 remove()

Deletes a file.

Example

remove("oldreport.txt");

1.11.42 Temporary Files

Function: tmpfile()

Creates temporary file automatically deleted after program termination.

1.11.43 Command Line Arguments

main() can receive arguments from command prompt.

Syntax

int main(int argc, char *argv[])

1.11.44 Example

Command:

app.exe India Chennai 2026

Values:

argc = 4
 
argv[0] = app.exe
argv[1] = India
argv[2] = Chennai
argv[3] = 2026

Applications of File Handling

Banking Systems
Payroll Management
Student Information Systems
E-Commerce Applications
Medical Records
Inventory Control
Library Management

Summary

Files provide permanent storage.
fopen() opens a file.
fclose() closes a file.
fgetc() and fputc() handle characters.
fgets() and fputs() handle strings.
fscanf() and fprintf() perform formatted I/O.
fread() and fwrite() process binary data.
fseek(), ftell(), and rewind() enable random access.
feof() and ferror() help detect file conditions.
File handling is essential for real-world software development.

Verify Comprehension: Technical Knowledge Assessment

Click your choice for each question to view feedback immediately. Complete all questions to evaluate your metric score.