File Handling in C

File Handling in C is used to create, open, read, write, modify, and close files. It allows programs to store data permanently in secondary storage instead of keeping it only in memory.

C provides several built-in functions such as fopen(), fclose(), fprintf(), fscanf(), fgets(), fputs(), fread(), and fwrite() for file operations.

Why Use File Handling?

Store data permanently.
Read previously saved data.
Handle large amounts of information.
Exchange data between programs.
Maintain records such as student, employee, and banking data.

File Pointer

Before performing any file operation, a file pointer is required.

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FILE *fptr;

FILE is a predefined structure available in the <stdio.h> header file.

Opening a File

The fopen() function is used to open a file.

Syntax

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FILE *fopen("file_name", "mode");

Example

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#include <stdio.h>

int main()
{
    FILE *fptr;

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

    if(fptr == NULL)
    {
        printf("File not found");
    }

    return 0;
}

Syntax of fopen()

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FILE *fopen(filename, mode);

Parameters

filename → Name or path of the file.
mode → Specifies how the file will be opened.

File Opening Modes

Read Mode

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"r"

Opens an existing file for reading.
Returns NULL if file does not exist.

Write Mode

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"w"

Opens file for writing.
Creates file if it does not exist.
Deletes old content if file already exists.

Append Mode

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"a"

Opens file for appending.
New data is added at the end of the file.

Read and Write Mode

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"r+"

Allows reading and writing.
File must already exist.

Write and Read Mode

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"w+"

Allows reading and writing.
Creates a new file if needed.
Old content is removed.

Append and Read Mode

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"a+"

Allows reading and appending.
Creates file if it does not exist.

Creating a File

A file can be created using write or append modes.

Example

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#include <stdio.h>

int main()
{
    FILE *fptr;

    fptr = fopen("file.txt", "w");

    if(fptr == NULL)
        printf("File creation failed");
    else
        printf("File created successfully");

    fclose(fptr);

    return 0;
}

Output

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File created successfully

Writing to a File

The following functions can write data into a file:

fprintf()
fputs()
fputc()
fwrite()

Using fprintf()

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#include <stdio.h>

int main()
{
    FILE *fptr;

    fptr = fopen("file.txt", "w");

    fprintf(fptr, "Welcome to C Programming");

    fclose(fptr);

    return 0;
}

Using fputs()

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#include <stdio.h>

int main()
{
    FILE *fptr;

    fptr = fopen("file.txt", "w");

    fputs("Hello Students", fptr);

    fclose(fptr);

    return 0;
}

Reading from a File

The following functions can read data from a file:

fscanf()
fgets()
fgetc()
fread()

Using fgets()

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#include <stdio.h>

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

    fptr = fopen("file.txt", "r");

    fgets(str, 100, fptr);

    printf("%s", str);

    fclose(fptr);

    return 0;
}

Using fscanf()

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#include <stdio.h>

int main()
{
    FILE *fptr;
    char name[50];

    fptr = fopen("file.txt", "r");

    fscanf(fptr, "%s", name);

    printf("%s", name);

    fclose(fptr);

    return 0;
}

Closing a File

After completing file operations, always close the file using fclose().

Syntax

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fclose(file_pointer);

Example

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fclose(fptr);

Closing a file releases resources used by the file.

End Of File (EOF)

EOF stands for End Of File.

Many reading functions return EOF when the file ends.

Example

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char ch;

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

Moving File Pointer

The fseek() function is used to move the file pointer to a specific location.

Syntax

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fseek(file_pointer, offset, position);

Example

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fseek(fptr, 0, SEEK_SET);

Moves the pointer to the beginning of the file.

ftell()

Returns the current position of the file pointer.

Example

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long pos;

pos = ftell(fptr);

printf("%ld", pos);

rewind()

Moves the file pointer back to the beginning of the file.

Example

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rewind(fptr);

Binary Files in C

Binary files store data in binary format rather than text format.

Common binary modes:

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rb
wb
ab
rb+
wb+
ab+

Writing to a Binary File

The fwrite() function writes binary data into a file.

Syntax

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fwrite(ptr, size, count, file_pointer);

Example

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#include <stdio.h>

struct Student
{
    int id;
};

int main()
{
    FILE *fptr;
    struct Student s = {101};

    fptr = fopen("student.bin", "wb");

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

    fclose(fptr);

    return 0;
}

Reading from a Binary File

The fread() function reads binary data from a file.

Syntax

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fread(ptr, size, count, file_pointer);

Example

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#include <stdio.h>

struct Student
{
    int id;
};

int main()
{
    FILE *fptr;
    struct Student s;

    fptr = fopen("student.bin", "rb");

    fread(&s, sizeof(s), 1, fptr);

    printf("%d", s.id);

    fclose(fptr);

    return 0;
}

Output

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Common File Functions

fopen()

Creates or opens a file.

fclose()

Closes a file.

fprintf()

Writes formatted data to a file.

fscanf()

Reads formatted data from a file.

fputs()

Writes a string to a file.

fgets()

Reads a string from a file.

fputc()

Writes a single character.

fgetc()

Reads a single character.

fwrite()

Writes binary data.

fread()

Reads binary data.

fseek()

Moves the file pointer.

ftell()

Returns current file pointer position.

rewind()

Moves file pointer to the beginning.

Summary

File handling is used to store and retrieve data permanently.
fopen() opens or creates a file.
fprintf(), fputs(), and fwrite() are used for writing.
fscanf(), fgets(), and fread() are used for reading.
fclose() closes the file.
fseek(), ftell(), and rewind() help manage file positions.
Binary files use fwrite() and fread() for efficient storage and retrieval.