ft = ftell(fd);
printf("ftell %d\n", ft); //-1
ft = fseek(fd, 0,SEEK_END);
printf("SEEK_END %d\n", ft); //-1
if (ft = -1)
{
 printf("ERROR: %s\n", strerror(errno)); //illegal seek.
}

char *gc;
rfcomm = fopen("/dev/rfcomm0", "rb+");
if(rfcomm == NULL)
{
 perror("Error:");           
}
fread(&gc, 1, 1, rfcomm); //works fine
*gc = 0x31;
fwrite( gc, 1, 1, rfcomm); //works fine

ft = ftell(fd);
printf("ftell %d\n", ft); //-1
ft = fseek(fd, 0,SEEK_END);
printf("SEEK_END %d\n", ft); //-1
if (ft = -1)
{
 printf("ERROR: %s\n", strerror(errno)); //illegal seek.
}

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


int main()
{
    int i;
    char c;
    FILE *fd;    
    int ft;


    printf("Wait for BT to establish\n");

    fd = fopen("/dev/rfcomm0", "rb+");

    if(fd == NULL)
    {
        perror("Failed to open /dev/rfcomm0");
        exit(128);
    }

    sleep(1);
    i = 0;

    while(i++ < 5)
    {
        sleep(1);
        ft = feof(fd);

        if (!ft)
        {
            printf("feof %d\n", ft);

            if(!fread(&c, 1, 1, fd)){break;};
            printf("read: %c\n", c);

            ft = fseek(fd, 1,SEEK_CUR);
            printf("SEEK_CUR %d\n", ft);
            ft = ftell(fd);
            printf("ftell %d\n", ft);
            ft = fseek(fd, 0L, SEEK_SET);
            printf("SEEK_SET %d\n", ft);

            if (ft = -1)
            {
                printf("ERROR: %s\n", strerror(errno));
            }

            //fflush(fd);
            clearerr (fd);
            printf("------------------\n\n", ft);

        }
        else
        {
             printf("--------------\n\n", ft);
        }
    }

    c = 'D';
    count = fwrite(&c, 1, 1, fd);
    fflush(fd);
    printf("Wrote %c, %zu byte(s).\n", c, count);

    sleep(1);
    fclose(fd);

    return 0;
}