Re: Read binary data file
Gordon Beaton wrote:
On Sat, 01 Sep 2007 23:39:52 GMT, Mike Schilling wrote:
On some OS's you could have created a memory-mapped file at whatever
address you provided, which lets you both use absolute addresses and
avoid the startup overhead by letting the file page itself in. Yours
is a nice "with simple tools" solution.
There are many components that make up the address space of an
application, and there is no guarantee that the same block of
addresses will always be available to the application. A program that
depends on that particular feature of mmap() is extremely fragile and
can't be expected to work across upgrades of the software or any of
the libraries it depends on. That might be ok for hobby projects, but
I'd never ship such a beast to a customer.
I'm not really familiar with mmap(); wouldn't it be possible to choose a
starting address well out of the possible end address of the application
proper? I was actually thinking of VMS, where the address could be in a
part of virtual memory that isn't used by the application at all.
In any case, if it's possible to allocate enough contiguous virtual memory
at some location, all that's needed is to adjust the stored addresses by the
difference [1], and you can still page the file in as needed. If you're not
sure of contiguous memory, you effectively have the OP's solution of (chunk,
offset) pairs.
Though if you're doing this, it's more logical to store offsets to the start
of the file rather than addresses.