#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>



int main ( int argc, char *argv[])
{
    char buf[64];

    if (argc != 3) {
	printf("args: <tmpfile> <0 or 1 to call fflush or not>");
	return -1;
    }

    int fd;

    if ((fd = open (argv[1], O_TRUNC | O_CREAT | O_WRONLY, 0600)) < 0) {
	printf ("failed to create/trunc file '%s' - %s\n", argv[1], strerror (errno));
	return -1;
    }


    const char *data = "0123456789abcdef";

    write (fd, data, strlen (data));
    fsync (fd);
    close (fd);
    fd = -1;

    FILE *f = fopen (argv[1], "rb+");

    if (f == NULL) {
	printf ("failed to open data file\n");
	return -1;
    }

    printf ("data file = '%s'\ntruncating at pos=10, remain = '%s'\n", data, &data[10]);
    fread (buf, 1, 8, f);  // prime the internal stream buffer

    fseek (f, 10, SEEK_SET);
    ftruncate (fileno (f), 10);
    if (*argv[2] == '1') {
	printf ("   flush FILE, will see following read contain NO data \n");
	fflush (f);
    }
    else {
	printf ("NO flush FILE, will see following read contain data\n");
    }

    int r = fread (buf, 1, sizeof (buf), f);
    buf[r] = '\0';
    printf ("fread %ld - '%s'\n", r, buf);
    fclose (f);

    return 0;
}