Is there a way to go to the beginning of a file and at a specified index with fgetc in C?

Question

For my algorithm, I would like to backtrack after going through all the chars in a file back to specific index char. For example, I have a file with ABCDEF, I want to access in the order ABCDEF then BCDEF then CDEF and so on. Is there a way I can do that with just fgetc and no string buffer?

  FILE *file = fopen("temp.txt", "r");
  int c;  
  while (1) {
    c = fgetc(file);
    if (feof(file)) {
      break;
    }
  // Access and print char
  }

Answer 1

You'll probably want to handle edge cases and error more cleanly than this, but...:

#include <stdio.h>
#include <stdlib.h>

FILE *
xfopen(const char *path, const char *mode)
{
        FILE *fp = path[0] != '-' || path[1] != '\0' ? fopen(path, mode) :
                *mode == 'r' ? stdin : stdout;
        if( fp == NULL ) {
                perror(path);
                exit(EXIT_FAILURE);
        }
        return fp;
}

int
main(int argc, char **argv)
{
        int c;
        long offset = 0;
        FILE *ifp = argc > 1 ? xfopen(argv[1], "r") : stdin;

        while( fseek(ifp, offset++, SEEK_SET) == 0 ) {
                while( (c = fgetc(ifp)) != EOF ) {
                        putchar(c);
                }
                if( ferror(ifp) ) {
                        return EXIT_FAILURE;
                }
                if( offset == ftell(ifp) ) {
                        break;
                }
        }
        return EXIT_SUCCESS;
}