C File I/O Basics

C File I/O Basics – Read and Write Files in C

In C programming, file I/O allows your program to read from and write to files on disk. This is essential for storing data permanently beyond program execution.

📦 File I/O Functions

• fopen() – Open a file
• fprintf() / fscanf() – Write/read formatted data
• fclose() – Close a file
• fgets() / fputs() – Read/write strings

📝 Example: Write to a File

This example writes text to a file called output.txt.

#include <stdio.h>

int main() {
    FILE *fp = fopen("output.txt", "w"); // Open file for writing
    if (fp == NULL) {
        printf("Error opening file!\n");
        return 1;
    }

    fprintf(fp, "Hello, file I/O in C!\n");
    fclose(fp); // Always close the file

    printf("Data written to file successfully.\n");
    return 0;
}
  

📝 Example: Read from a File

This reads and prints content from output.txt.

#include <stdio.h>

int main() {
    char buffer[100];
    FILE *fp = fopen("output.txt", "r"); // Open file for reading
    if (fp == NULL) {
        printf("File not found!\n");
        return 1;
    }

    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        printf("%s", buffer); // Print each line
    }

    fclose(fp);
    return 0;
}
  

🛠 File Modes in fopen()

🎯 Practice Tip

Try creating your own file, writing different data types using fprintf, and then reading them back. Remember to always close your files with fclose()! 🗂️