C File Handling

File handling in C involves reading and writing data to and from files. The standard library in C provides functions and data types to work with files. Here’s an overview of file handling in C.

Opening a File:

• To work with a file, you first need to open it using the fopen() function. This function takes two arguments: the file name (including the path) and the mode in which you want to open the file.
• Common modes include "r" for reading, "w" for writing (creates a new file or overwrites an existing one), "a" for appending (adds data to the end of an existing file), "rb" and "wb" for binary reading and writing, and more.
• Example:

#include <stdio.h>

int main() {
    FILE *file = fopen("example.txt", "w");
    
    if (file == NULL) {
        perror("Error opening the file");
        return 1;
    }

    // Your code here

    fclose(file);
    return 0;
}

Reading from a File:

• You can read data from a file using functions like fread(), fgets(), or fscanf().
• Example using fgets():

#include <stdio.h>

// Assuming 'file' is declared and opened somewhere in the code

char buffer[100];

if (fgets(buffer, sizeof(buffer), file) != NULL) {
    printf("Data read from the file: %s\n", buffer);
}

Writing to a File:

• You can write data to a file using functions like fwrite(), fputs(), or fprintf().
• Example using fprintf():

c fprintf(file, "This is a line of text.\n");

Closing a File:

• It’s essential to close the file when you’re done using it to free up system resources and ensure that data is written to the file.
• Use the fclose() function to close the file.
• Example:

c fclose(file);

Checking for Successful Operations:

• After opening, reading, or writing to a file, it’s a good practice to check if the operation was successful.
• Most file-related functions return NULL or a specific value on failure.
• Use feof() to check for the end of the file.
• Example:

c if (feof(file)) { 
  printf("End of file reached.\n"); 
}

Error Handling:

• Handle errors that may occur during file operations using functions like perror() or by checking the return values of file-related functions.
• Example:

c if (file == NULL) { 
  perror("Error opening the file"); 
  return 1; 
}

Binary File Handling:

• For binary file handling, use "rb" and "wb" modes and functions like fread() and fwrite() to read and write binary data.

Here’s a simple example that demonstrates file handling by writing and reading a line of text to/from a file:

#include <stdio.h>

int main() {
    FILE *file = fopen("example.txt", "w");
    if (file == NULL) {
        perror("Error opening the file");
        return 1;
    }

    fprintf(file, "This is a line of text.\n");
    fclose(file);

    file = fopen("example.txt", "r");
    if (file == NULL) {
        perror("Error opening the file");
        return 1;
    }

    char buffer[100];
    if (fgets(buffer, sizeof(buffer), file) != NULL) {
        printf("Data read from the file: %s", buffer);
    }

    fclose(file);

    return 0;
}

This program writes a line of text to “example.txt,” closes the file, and then reads and prints the same line of text from the file.