File Handling in C

File handling in C involves using a set of functions provided by the C Standard Library to perform operations on files, such as reading from, writing to, and managing files. Here’s a detailed overview:

File Handling in C Basics

In C, files are managed using file pointers. A file pointer is a variable of type FILE* that holds the address of a file structure used by the system to keep track of the file.

Header File in C

To perform file operations, you need to include the stdio.h header file:

#include <stdio.h>

Opening and Closing Files

To open a file, use the fopen() function. To close a file, use the fclose() function.

Opening a File:

FILE *file = fopen("filename.txt", "mode");

Modes for Opening Files

• "r": Read-only mode
• "w": Write-only mode (creates a new file or truncates an existing file)
• "a": Append mode (adds data to the end of the file)
• "r+": Read and write mode
• "w+": Read and write mode (creates a new file or truncates an existing file)
• "a+": Read and write mode (appends data to the end of the file)

Example:

FILE *file = fopen("example.txt", "r");
if (file == NULL) {
    printf("Error opening file!\n");
}

Closing a File:

fclose(file);

Reading from and Writing to Files

Reading:

• fgetc(FILE *stream): Reads the next character from the file.
• fgets(char *str, int n, FILE *stream): Reads a line from the file into str.
• fread(void *ptr, size_t size, size_t count, FILE *stream): Reads count elements of size bytes from the file.

Example:

char c;
while ((c = fgetc(file)) != EOF) {
    putchar(c);
}

Writing:

• fputc(int char, FILE *stream): Writes a character to the file.
• fputs(const char *str, FILE *stream): Writes a string to the file
• fwrite(const void *ptr, size_t size, size_t count, FILE *stream): Writes count elements of size bytes to the file.

Example:

fprintf(file, "Hello, World!\n");

File Positioning

• fseek(FILE *stream, long int offset, int whence): Moves the file pointer to a specified location.
  • offset: Number of bytes to move.
  • whence: Position from where to move (SEEK_SET, SEEK_CUR, SEEK_END)

Example:

fseek(file, 0, SEEK_SET); // Move to the beginning of the file

• ftell(FILE *stream): Returns the current position of the file pointer.
• rewind(FILE *stream): Sets the file position back to the beginning of the file.

File Status Functions

• feof(FILE *stream): Checks for the end-of-file condition.
• ferror(FILE *stream): Checks for errors during file operations.
• clearerr(FILE *stream): Clears the end-of-file and error indicators.

Example Program

Here’s a simple example demonstrating file handling in C:

#include <stdio.h>

int main() {
    // Open a file for writing
    FILE *file = fopen("example.txt", "w");
    if (file == NULL) {
        printf("Error opening file for writing!\n");
        return 1;
    }

    // Write to the file
    fprintf(file, "Hello, File Handling in C!\n");
    fclose(file);  // Close the file

    // Open the file for reading
    file = fopen("example.txt", "r");
    if (file == NULL) {
        printf("Error opening file for reading!\n");
        return 1;
    }

    // Read and print the file contents
    char buffer[100];
    while (fgets(buffer, sizeof(buffer), file)) {
        printf("%s", buffer);
    }

    fclose(file);  // Close the file
    return 0;
}

Conclusion

File handling in C is essential for many programming tasks, from simple file reading and writing to complex file manipulations. Understanding these basic functions and concepts will help you work with files effectively in your C programs.