#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>

#define O_LARGEFILE 0100000

#define SCOOP_SIZE      64
#define PLOTSIZE        262144
#define S_IROTH 0004
#define S_IRGRP 0040 
...

        int fh = open(argv[1], O_LARGEFILE | O_RDONLY);

        if(fh < 0) {
                printf("File %s not found\n", argv[1]);
                exit(-1);
        }

        struct stat sh;
        fstat(fh, &sh);

        unsigned long long int expect = (unsigned long long int)nonces * PLOTSIZE;

        if(((long long) sh.st_size) != expect) {
                printf("File not complete. Expected size: %llu, actual size: %llu\n", expect, (long long) sh.st_size);
                exit(-1);
        }
...

#define _LARGEFILE_SOURCE
#define _FILE_OFFSET_BITS 64
#define __USE_LARGEFILE64