File In C (Eng.Medium)

 

File in C: - A file in C is a collection of data stored permanently on a storage device (hard disk).

OR

A file is used to store data permanently so that it can be used later, even after the program ends.

Advantages and Disadvantages of File in C

 Advantages of File in C

1. Data is stored permanently
2. Data can be used again after program ends
3. Can store large amount of data
4. Easy to read and write data
5. Useful for records and databases
6. Binary files provide fast processing

 Disadvantages of File in C

1. File handling is slower than memory access
2. Binary files are not human readable
3. File operations are more complex than variables
4. Data may be lost if file is not closed properly
5. Error handling is required

Types of Files in C

Files in C can be classified in two ways:

(A) Based on Storage Format

Text File:- A text files stores data in human-readable form. The data is saved as characters, so it can be easily opened and read using applications like Notepad. Text files are easy to understand and are commonly used to store simple data such as names, marks, or messages. However, they require more storage space and are slower than binary files.

2 Binary File:- A binary file stores data in binary format (0 and 1). It is not readable by humans and cannot be opened in Notepad. Binary files are faster and take less storage space compared to text files. They are mainly used to store large amounts of data such as records, structures, and images.

(B) Based on Access Method

3 Sequential File:- A sequential file stores data in sequence, and the data is accessed one record after another. To read any data, we must start reading from the beginning of the file. Text files usually follow sequential access. This method is simple but time-consuming for large files.

4 Random File:- A random file allows direct access to data from any location in the file. Using functions like fseek(), we can move the file pointer to a specific position and read or write data directly. This method is fast and efficient and is mainly used in binary files for record-based systems.

File Pointer:- A file pointer is a special pointer used to handle files in C. It is used to connect program to the file. It is used in all file operations

Declaration:

FILE *fp;

Opening a File

Opening a file means creating a connection between the program and the file stored on the disk. In C, the fopen() function is used to open a file. It requires two arguments: the name of the file and the mode in which the file is to be opened. The mode decides whether the file will be opened for reading, writing, appending, or in binary form. If the file is opened successfully, fopen() returns a file pointer; otherwise, it returns NULL. Therefore, it is always important to check whether the file has been opened successfully before performing any operation on it.

fopen() Function :- The fopen() function is used to open a file in C. It creates a connection between the program and the file. If the file opens successfully, it returns a file pointer; otherwise, it returns NULL.

Syntax:

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

 File Opening Modes

Text File Modes

Mode	Meaning
r	Open text file for reading
w	Open text file for writing (old data erased)
a	Open text file for appending data
r+	Read and write text file
w+	Write and read text file
a+	Append and read text file

 

Binary File Modes

Mode	Meaning
rb	Open binary file for reading
wb	Open binary file for writing
ab	Open binary file for appending
rb+	Read and write binary file
wb+	Write and read binary file
ab+	Append and read binary file

 

5Closing a File

Function Used: The fclose() function is used to close an open file in C. It saves all data properly and releases the memory used by the file.

fclose(fp);

Text File Input Functions

1 fprintf():- fprintf() is used to write formatted data to a text file. It works like printf() but writes output into a file instead of the screen. It is useful for writing numbers, characters, and strings in a formatted way.

Syntax:

fprintf(fp, "format string", variables);

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2 fputc():- fputc() is used to write a single character to a text file. It writes one character at a time at the current file position and is useful for character-by-character file writing.

Syntax:

fputc(character, fp);

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3 fputs():- fputs() is used to write a string to a text file. It writes the complete string to the file but does not automatically add a new line at the end.

Syntax:

fputs(string, fp);

Text File Input Functions

1-fscanf():- fscanf() is used to read formatted data from a text file. It works like scanf() but reads input from a file instead of the keyboard. It is used to read numbers, characters, and strings in a formatted form.

Syntax:

fscanf(fp, "format string", &variables);

 2 fgetc():- fgetc() is used to read a single character from a text file. It reads one character at a time from the current file position and returns the character read from the file.

Syntax:

fgetc(fp);

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3 fgets():- fgets() is used to read a string from a text file. It reads characters from the file until a newline is found or the given limit is reached. It is mainly used to read one line at a time.

Syntax:

fgets(string, size, fp);

Simple C program using fprintf() and fscanf().

#include <stdio.h>

int main() {

    FILE *fp;

    int a = 50, b = 75, x, y;

    char name[20] = "Ashok";

    char str[20];

    fp = fopen("data.txt", "w");

    fprintf(fp, "%d %d\n", a, b);

    fprintf(fp, "%s\n", name);

    fclose(fp);

    fp = fopen("data.txt", "r");

    fscanf(fp, "%d %d", &x, &y);

    fscanf(fp, "%s", str);

    printf("%d %d\n", x, y);

    printf("%s\n", str);

    fclose(fp);

    return 0;

}

Writing to Binary File

 fwrite():- fwrite() is used to write data to a binary file. It stores data in binary form, which is faster and uses less space. It is commonly used to write numbers, arrays, and structures into a file.

Syntax:

fwrite(address, size, count, fp);

Reading from Binary File  

fread():- fread() is used to read data from a binary file. It reads data in the same order in which it was written. It is used to retrieve binary data such as integers, floats, arrays, and structures.

Syntax:

fread(address, size, count, fp);

Simple C program using fwrite() and fread().

#include <stdio.h>

int main() {

    FILE *fp;

    int a = 100;

    float b = 23.5;

    char ch = 'X';

    int x;

    float y;

    char z;

    fp = fopen("data.bin", "wb");

    fwrite(&a, sizeof(a), 1, fp);

    fwrite(&b, sizeof(b), 1, fp);

    fwrite(&ch, sizeof(ch), 1, fp);

    fclose(fp);

    fp = fopen("data.bin", "rb");

    fread(&x, sizeof(x), 1, fp);

    fread(&y, sizeof(y), 1, fp);

    fread(&z, sizeof(z), 1, fp);

    printf("%d\n%.2f\n%c\n", x, y, z);

    fclose(fp);

    return 0;

}

Difference Between Text File and Binary File

Text File	Binary File
Stores data in readable (character) form	Stores data in binary (0 and 1) form
Can be opened and read using Notepad	Cannot be read using Notepad
Uses functions like fprintf() and fscanf()	Uses functions like fwrite() and fread()
Requires more storage space	Requires less storage space
Slower compared to binary files	Faster for reading and writing

 

Random Access in Files (Paragraph)

Random access in C allows us to read or write data at any position in a file without reading it sequentially from the beginning. It is mostly used with binary files. Functions like fseek(), ftell(), and rewind() help move the file pointer to a specific location, find the current position of the pointer, or return it to the start of the file, making file operations faster and efficient.

 

1fseek():-Moves the file pointer to a specific position in a file.
Syntax:

fseek(fp, offset, origin);

C program using fseek() to access a specific record in a binary file.

 

#include <stdio.h>

#include <stdlib.h>

int main() {

    FILE *fp;

    int numbers[5] = {10, 20, 30, 40, 50};

    int num;

    fp = fopen("data.bin", "wb");

    fwrite(numbers, sizeof(int), 5, fp);

    fclose(fp);

    fp = fopen("data.bin", "rb");

    fseek(fp, 2 * sizeof(int), SEEK_SET);

    fread(&num, sizeof(int), 1, fp);

    printf("%d\n", num);

    fclose(fp);

    return 0;

}

2 ftell():- Returns the current position of the file pointer in a file.
Syntax:

ftell(fp); 

3rewind():- Moves the file pointer back to the beginning of the file.
Syntax:

rewind(fp);