Unit 10: File Handling in C Programming | B. Sc Year: III

🧭 Introduction

So far, all the C programs you wrote lost their data once the program ended.
But in real-world applications, data must be stored permanently so it can be used again later.

This is where file handling comes in.

Using file handling, C programs can:

• Store data permanently on disk

• Read data whenever needed

• Update, append, or manage records

File handling is widely used in:

• Student record systems

• Banking software

• Inventory management

• Report generation

This unit is very important for exams, especially TU long questions and programs.

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🔑 Key Concepts (Simple Explanation)

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1️⃣ What is File Handling?

File handling is the process of:

• Creating files

• Writing data into files

• Reading data from files

A file is a collection of data stored permanently on secondary storage (hard disk).

Exam Definition ✅

File handling in C is a technique used to store and retrieve data permanently using files.

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2️⃣ Types of Files in C

C supports two main types of files:

🔹 Text Files

• Data stored as characters

• Human-readable

• Example: .txt files

✅ Used for reports, logs, plain text

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🔹 Binary Files

• Data stored in binary form (0s and 1s)

• Faster and more efficient

• Not human-readable

✅ Used for databases, records, images

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3️⃣ FILE Pointer

C uses a FILE pointer to access files.

Declaration:

FILE *fp;

✅ FILE is defined in <stdio.h>

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4️⃣ Opening and Closing a File

Open a file using fopen()

fp = fopen("file.txt", "mode");

Close a file using fclose()

fclose(fp);

✅ Always close files to prevent data loss.

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5️⃣ File Opening Modes

Mode	Meaning
"r"	Read
"w"	Write (creates new file)
"a"	Append
"r+"	Read & write
"w+"	Write & read
"a+"	Append & read

✅ Mode questions are very common in exams.

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6️⃣ Writing Data to a File

Using fprintf()

fprintf(fp, "Hello File");

Program Example: Write Data

#include <stdio.h>

int main() {
    FILE *fp;
    fp = fopen("data.txt", "w");

    fprintf(fp, "Welcome to File Handling in C!");
    fclose(fp);

    return 0;
}

✅ Creates and writes into data.txt.

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7️⃣ Reading Data from a File

Using fscanf()

fscanf(fp, "%s", data);

Program Example: Read Data

#include <stdio.h>

int main() {
    FILE *fp;
    char ch;

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

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

    fclose(fp);
    return 0;
}

✅ EOF marks the end of file.

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8️⃣ Character I/O File Functions

Function	Purpose
fgetc()	Read one character
fputc()	Write one character

Example:

fputc('A', fp);
char ch = fgetc(fp);

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9️⃣ File Handling with Structures

Example: Write Structure to File

struct student {
    int roll;
    char name[20];
};

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

✅ Often asked as an advanced exam question.

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🔟 Binary File Functions

Function	Use
fread()	Read binary data
fwrite()	Write binary data

Syntax:

fwrite(&data, sizeof(data), 1, fp);
fread(&data, sizeof(data), 1, fp);

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1️⃣1️⃣ Error Handling in Files

Always check if the file opened successfully:

if (fp == NULL) {
    printf("File cannot be opened");
    return 1;
}

✅ Gives extra safety and marks.

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🔍 Difference Between Text File and Binary File

Text File	Binary File
Human readable	Not readable
Slower	Faster
Stored as characters	Stored as raw data
Easy to edit	More secure

✅ Frequently asked in theory questions.

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📝 Important Exam Questions

1. What is file handling in C?

2. Types of files in C

3. Explain file opening modes

4. Write a program to write and read a file

5. Difference between text file and binary file

6. What is FILE pointer?

7. Explain fopen() and fclose()

8. Explain fread() and fwrite()

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🎯 Exam Tips / Key Points

• Always include <stdio.h>

• Use correct file mode

• Close file after use

• Check for NULL pointer

• Use EOF while reading

• Programs from this unit are high scoring

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✅ Short Summary

In Unit 10, you learned:

• What file handling is and why it is needed

• Types of files (text and binary)

• FILE pointer and file modes

• File input/output functions

• Writing and reading files

• Error handling in files

File handling allows programs to store data permanently, making them suitable for real-world applications.

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