On Thu, Nov 12, 2009 at 12:06 PM, Mark Bucciarelli <[email protected]> wrote: > The file holds a number of structs each of size size_t. I stat > the file, compute records_n, then make sure the product of > records_n and struct size is exactly equal to the file size.
The size of size_t is variable, so you need to decide whether you actually meant 4 bytes or 8 bytes. Also, the length argument to mmap is size_t, not off_t, so even if you did the multiply check properly, you'd be truncating on the mmap call. > > The ptrdiff_t question is similar: > > p0 = (mystruct *) mmap(...); > if (p0 == -1) err(1, "boom!"); > for (p = p0; p < p0 + records_n; p++) > do_something_with(p); > > Is there a portable way to code these two tasks? What's wrong with p0 + records_n?
