Re: [boost] interprocess with unordered_map

Subject: Re: [boost] interprocess with unordered_map
From: Joel (jdy_at_[hidden])
Date: 2012-03-17 00:53:27

Ion Gaztañaga <igaztanaga <at> gmail.com> writes:

> 
> El 15/03/2012 23:18, Olaf van der Spek escribió:
> > 2012/3/15 Ion Gaztañaga<igaztanaga <at> gmail.com>:
> >> El 15/03/2012 3:14, Joel Young escribió:
> >>>
> >>> Can the interprocess::basic_string be modified to allow these conversions?
> >>>
> >>> I hate having to do:
> >>>
> >>> key_val             = "fruitcake";
> >>> db.find(key_val);
> >>
> >> place the string in shared memory. I don' think it could be implicitly
> >> constructible from char* or std::string.

My code above used the assignment operator to convert it.  The constructor can
do it also.  If not, then at least provide a convenience function to do it!

> > But there's no (good) reason for the input to be required to be in
> > shared memory.

Exactly.  I've got my container in the mapped file or shared memory.  Why should
I want to clutter up the shared memory with a temporary?  Especially if I'm just
doing a find in a read-only chunk of memory!
 
> A shared memory allocator is designed to allocate from a managed shared 
> memory segment. And this requires a base address of that shared memory 
> segment . And even with std::string you need to build a temporary string 
> to compare it with the ones stored in the container.

But the temporary string isn't used for anything!  I create a temporary string,
allocated into a DIFFERENT memory pool and it works just fine.  If I can create
an arbitrary basic_string with an allocator to a random place to serve as a
temporary, the library can darn well do it too!

Joel