Exercise 8.4.Write int fseek(FILE *fp, long offset, int origin).

Exercise 8.4. The standard library function int fseek(FILE *fp, long offset, int origin) is identical to lseek except that fp is a file pointer instead of a file descriptor and return value is an int status, not a position. Write fseek.



/* fseek: random access using file pointer */
int _fseek(_FILE *fp, long offset, int origin)
{
    unsigned nc; //discharged characters
    long rc = 0; //return code
   
    if(fp->flag.f_read)
    {
        if(origin == 1)
            offset -= fp->cnt;
        rc = lseek(fp->fd, offset, origin);
        fp->cnt = 0; //buffer is empty
    }
    else if(fp->flag.f_write)
    {
        if((nc = fp->ptr - fp->base) > 0)
            if(write(fp->fd, fp->base, nc) != nc)
                rc = -1;
        if(rc != -1) // no error
            rc = lseek(fp->fd, offset, origin);
    }
    return (rc == -1) ? -1 : 0;
}