File handling in C is accomplished using file pointers, which provide a way to access and manipulate files. A file pointer is a variable of type FILE*, used to keep track of the position within the file and manage file operations.

Basic Steps for File Handling

1. Declare a File Pointer:

   FILE *fp;
   

2. Open a File: Use the fopen function to open a file. It returns a file pointer or NULL if the operation fails.

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

   Common modes include:

   • "r": Read (file must exist)
   • "w": Write (creates a new file or truncates existing file)
   • "a": Append (writes data to the end of the file)
   • "r+": Read/Write (file must exist)
   • "w+": Read/Write (creates a new file or truncates existing file)
   • "a+": Read/Write (writes data to the end of the file)

3. Perform File Operations: Use various functions to read from or write to the file.

   • Writing to a File:

     fprintf(fp, "format", data);
     fputc('c', fp);
     fputs("string", fp);
     

   • Reading from a File:

     fscanf(fp, "format", &data);
     char c = fgetc(fp);
     char str[100];
     fgets(str, 100, fp);
     

4. Close the File: Use fclose to close the file and release resources.

   fclose(fp);
   

Example

Here's a complete example of writing to and reading from a text file using file pointers.

#include <stdio.h>

int main() {
    FILE *fp;

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

    // Write to the file
    fprintf(fp, "Hello, World!\n");
    fputs("This is a file handling example.\n", fp);

    // Close the file
    fclose(fp);

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

    // Read from the file
    char buffer[255];
    while (fgets(buffer, sizeof(buffer), fp) != NULL) {
        printf("%s", buffer);
    }

    // Close the file
    fclose(fp);

    return 0;
}

File Operations Summary

• fopen: Opens a file and returns a file pointer.
• fclose: Closes a file.
• fprintf, fputs, fputc: Write data to a file.
• fscanf, fgets, fgetc: Read data from a file.
• feof: Checks if the end of the file is reached.
• ferror: Checks for file operation errors.
• rewind: Sets the file position to the beginning of the file.
• ftell: Returns the current file position.
• fseek: Sets the file position to a specific location.

Using file pointers in C allows efficient and flexible file operations, essential for managing persistent data.