Re: [Boost-users] Memory mapped files

Subject: Re: [Boost-users] Memory mapped files
From: Gavin Lambert (boost_at_[hidden])
Date: 2019-01-23 22:24:26

On 23/01/2019 21:15, Simon Giddings wrote:
> Sorry, but this is a very specific Boost question as we are using the 
> Boost memory mapping system.

You still haven't indicated what library you're talking about.  There is 
no "Boost memory mapping system"; there may or may not be a particular 
library you are using.

But, as previously stated, C++ makes no particular guarantees about the 
memory layout of class objects and only very minimal guarantees about 
the layout of POD types.  This is especially true cross-platform and 
cross-toolset, but can bite you when you update the compiler or runtimes 
within a single platform, or even potentially from one run to another 
(eg. hash/map ordering can change).

If you want portability, then you need to use a serialisation library 
which implements portability (not all do) along with compatible data 
structures; but this is an entirely different animal from plain memory 
mapping.