C :: Read Doubles From A Binary File

I use the following function to read doubles from a binary file:

Code:

int64_t read_current(FILE *input, double *current, uint64_t position, uint64_t length)
{
printf("asked for %" PRIu64" samples
",length);
printf("reading from %" PRIu64 " to %" PRIu64 "
",position,position+length);
union{
double d;
uint64_t i;
}

[code]...

As long as position+length doesn't exceed the end of the file, all is well. However, if it does, weird things start to happen. In particular, the apparent length of the file (that is, the value of "read" after the function has finished) becomes dependent on "length"). I know that "position" is never past the end of the file.