Dharani Tech Edu Hub

Reading & Writing Files in C

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Introduction

In C programming, reading and writing files allow us to store and retrieve data permanently.

👉 This is important for real-world applications like databases, logs, and reports.

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File Pointer

FILE *fp;

👉 Used to access file

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Opening a File

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

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Writing to a File

👉 Using fprintf()

#include <stdio.h>

int main() {
    FILE *fp;

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

    fprintf(fp, "Welcome to Dharani Tech Edu Hub");

    fclose(fp);

    return 0;
}

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Output

👉 Creates file and writes data

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Reading from a File

👉 Using fgets()

#include <stdio.h>

int main() {
    FILE *fp;
    char str[100];

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

    fgets(str, sizeof(str), fp);

    printf("%s", str);

    fclose(fp);

    return 0;
}

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Output

Welcome to Dharani Tech Edu Hub

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Writing Multiple Lines

#include <stdio.h>

int main() {
    FILE *fp;

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

    fprintf(fp, "Line 1\n");
    fprintf(fp, "Line 2\n");

    fclose(fp);

    return 0;
}

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Reading Character by Character

#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;
}

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Output

👉 Displays file content character by character

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File Functions Table

Function	Purpose
fprintf()	Write formatted data
fgets()	Read line
fgetc()	Read character
fputc()	Write character

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Important Notes

• Always close file after use
• Use correct mode (r, w, a)
• Check if file opened successfully

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Common Mistakes

• ❌ Forgetting fclose()
• ❌ File not found error
• ❌ Wrong file mode
• ❌ Not checking NULL pointer

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Pro Tips

• ✔ Use fgets() for safe reading
• ✔ Use loops for reading files
• ✔ Handle file errors
• ✔ Practice file programs

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Conclusion

Reading and writing files is essential for handling data permanently in C. It helps in building real-world applications.

Master file handling to improve your programming skills.

👉 This article is part of Dharani Tech Edu Hub — where learning programming is made simple and practical.