Simple File System Program in C for Create, Read, and Write Operations
Learn how to build a simple file system in C that supports file creation, reading, and writing. Full source code with step-by-step explanations in easy words.
In this tutorial, we’ll implement a basic file system using the C programming language that allows you to:
-
Create a file
-
Write data to a file
-
Read data from a file
This type of small project helps you understand how file handling works in Operating Systems, especially how low-level file management can be simulated in user space.
🔍 What is a File System?
A file system is a way to organize and store files on a storage device like a hard drive or SSD. In Operating Systems, it handles file creation, reading, writing, permissions, and organization. For this project, we’ll simulate a tiny file system where we manually perform basic operations.
🎯 Program Goals
Our simple file system will support:
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Creating a new file (with a name)
-
Writing text content to that file
-
Reading and displaying content from a file
We’ll use file handling functions in C (fopen, fprintf, fscanf, etc.) to perform these operations.
🧑💻 C Code: Basic File System Program
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// Function declarations
void createFile(const char *filename);
void writeFile(const char *filename);
void readFile(const char *filename);
int main() {
int choice;
char filename[100];
while (1) {
printf("\n=== Simple File System Menu ===\n");
printf("1. Create File\n");
printf("2. Write to File\n");
printf("3. Read from File\n");
printf("4. Exit\n");
printf("Enter your choice: ");
scanf("%d", &choice);
getchar(); // to consume newline character
switch (choice) {
case 1:
printf("Enter filename to create: ");
fgets(filename, sizeof(filename), stdin);
filename[strcspn(filename, "\n")] = '\0'; // remove newline
createFile(filename);
break;
case 2:
printf("Enter filename to write to: ");
fgets(filename, sizeof(filename), stdin);
filename[strcspn(filename, "\n")] = '\0';
writeFile(filename);
break;
case 3:
printf("Enter filename to read from: ");
fgets(filename, sizeof(filename), stdin);
filename[strcspn(filename, "\n")] = '\0';
readFile(filename);
break;
case 4:
printf("Exiting program...\n");
exit(0);
default:
printf("Invalid choice! Please try again.\n");
}
}
return 0;
}
// Function to create an empty file
void createFile(const char *filename) {
FILE *fp = fopen(filename, "w"); // open in write mode
if (fp == NULL) {
printf("Error creating file!\n");
return;
}
printf("File '%s' created successfully.\n", filename);
fclose(fp);
}
// Function to write content to a file
void writeFile(const char *filename) {
FILE *fp = fopen(filename, "a"); // append mode
if (fp == NULL) {
printf("File not found!\n");
return;
}
char data[500];
printf("Enter text to write (end with ENTER):\n");
fgets(data, sizeof(data), stdin);
fprintf(fp, "%s", data);
printf("Data written to '%s' successfully.\n", filename);
fclose(fp);
}
// Function to read content from a file
void readFile(const char *filename) {
FILE *fp = fopen(filename, "r"); // open in read mode
if (fp == NULL) {
printf("File not found!\n");
return;
}
char ch;
printf("\n--- File Contents of '%s' ---\n", filename);
while ((ch = fgetc(fp)) != EOF) {
putchar(ch);
}
printf("\n--- End of File ---\n");
fclose(fp);
}
🧠 Step-by-Step Explanation
🔹 main() Function
-
Shows a menu to the user using
printf. -
Takes user input for which operation to perform.
-
Based on choice, calls one of the functions:
createFile(),writeFile(), orreadFile().
🔹 createFile() Function
FILE *fp = fopen(filename, "w");
-
Opens a new file in write mode.
-
If the file doesn’t exist, it creates one.
-
If it exists, it clears existing content.
-
fclose(fp)closes the file after operation.
🔹 writeFile() Function
FILE *fp = fopen(filename, "a");
-
Opens the file in append mode.
-
Takes input text from user using
fgets(). -
Writes the input to the file using
fprintf(). -
Appends content without deleting previous text.
🔹 readFile() Function
char ch;
while ((ch = fgetc(fp)) != EOF) {
putchar(ch);
}
-
Opens file in read mode.
-
Reads each character using
fgetc()until the end of file (EOF). -
Displays content using
putchar().
⚙️ How to Compile and Run
Using GCC compiler:
gcc file_system.c -o file_system
./file_system
Make sure your terminal/IDE is in the same folder where your file_system.c file is saved.
✅ Output Example
=== Simple File System Menu ===
1. Create File
2. Write to File
3. Read from File
4. Exit
Enter your choice: 1
Enter filename to create: myfile.txt
File 'myfile.txt' created successfully.
Enter your choice: 2
Enter filename to write to: myfile.txt
Enter text to write (end with ENTER):
Hello from my mini file system!
Data written to 'myfile.txt' successfully.
Enter your choice: 3
Enter filename to read from: myfile.txt
--- File Contents of 'myfile.txt' ---
Hello from my mini file system!
--- End of File ---
📚 Conclusion
You just created a basic file system simulation using C programming. This simple project is a great introduction to:
-
File creation
-
Writing data
-
Reading data
-
Menu-based user interaction
Understanding such simulations helps in grasping the fundamentals of Operating Systems, especially how they manage files.
🔑 Key Takeaways
-
fopen()is used for creating and opening files. -
fprintf()andfputs()write data to files. -
fgetc()reads characters from a file. -
Always close files using
fclose()to avoid memory leaks.
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