C Tutorial

📌 File Pointers in C

File pointers in C are special pointers used to handle files. Every time you work with a file in C, you use a file pointer of type FILE * to manage it.

🔹 Declaring a File Pointer

FILE *fp;
  

Here, fp is a file pointer that can be used with functions like fopen(), fclose(), fread(), etc.

🔹 Opening a File with a File Pointer

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

This opens the file data.txt in read mode. The pointer fp now points to the file's memory structure.

✨ Full Example Using File Pointer

#include <stdio.h>

int main() {
    FILE *fp;
    fp = fopen("example.txt", "w");  // Open for writing

    if (fp == NULL) {
        printf("File cannot be opened.\n");
        return 1;
    }

    fprintf(fp, "File pointer example.");  // Write to file
    fclose(fp);  // Close the file

    return 0;
}
  

🔹 File Pointer as File Position Indicator

The file pointer also keeps track of the current read/write position in the file. Functions like fseek(), ftell(), and rewind() can manipulate this position.

✨ Example Using fseek() and ftell()

#include <stdio.h>

int main() {
    FILE *fp = fopen("seek_example.txt", "w+");
    fputs("Hello File!", fp);

    fseek(fp, 0, SEEK_END);  // Move to end
    printf("Position: %ld", ftell(fp));  // Print position

    rewind(fp);  // Move back to beginning
    char str[20];
    fgets(str, 20, fp);
    printf("\\nContent: %s", str);

    fclose(fp);
    return 0;
}