rewind()

#include <stdio.h>
#include <conio.h>
void main() {
  FILE *fp;
  char c;
  clrscr();
  fp = fopen("file.txt", "r");
  while( (c = fgetc(fp) ) != EOF) {
    printf("%c", c);
  }
  rewind(fp); // move the file pointer to the beginning of the file
  while( (c = fgetc(fp) ) != EOF) {
    printf("%c", c);
  }
  fclose(fp);
  getch();
}
// output
// Hello World! Hello World!