Dharani Tech Edu Hub

File Modes in C

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Introduction

File modes in C define how a file should be opened and used.

👉 They control whether you can:

• Read
• Write
• Append data

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What are File Modes?

File modes are:
👉 Options used with fopen() to specify file operations

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Syntax

FILE *fp = fopen("filename", "mode");

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Types of File Modes

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Basic File Modes

Mode	Description
r	Read (file must exist)
w	Write (creates/overwrites file)
a	Append (adds data)

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Advanced File Modes

Mode	Description
r+	Read & Write (file must exist)
w+	Read & Write (creates new file)
a+	Read & Append

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Binary File Modes

Mode	Description
rb	Read binary
wb	Write binary
ab	Append binary

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Example: Using Different Modes

#include <stdio.h>

int main() {
    FILE *fp;

    // Write mode
    fp = fopen("test.txt", "w");
    fprintf(fp, "Hello\n");
    fclose(fp);

    // Append mode
    fp = fopen("test.txt", "a");
    fprintf(fp, "World\n");
    fclose(fp);

    // Read mode
    char str[50];
    fp = fopen("test.txt", "r");
    fgets(str, sizeof(str), fp);
    printf("%s", str);
    fclose(fp);

    return 0;
}

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Output

Hello

👉 File contains:

Hello
World

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Important Notes

• r → file must exist
• w → deletes old content
• a → adds data at end
• + → allows both read & write

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Common Mistakes

• ❌ Using wrong mode
• ❌ Not closing file
• ❌ Data loss with w mode
• ❌ Not checking file pointer

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Pro Tips

• ✔ Choose correct mode carefully
• ✔ Use a to avoid data loss
• ✔ Always close files
• ✔ Handle errors properly

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Conclusion

File modes are essential for controlling file operations in C. Choosing the right mode ensures proper data handling.

Master file modes for efficient file management.

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