Re: [Boost-users] [interprocess] example for boost::interprocess::map where the key is something in shared memory

From: Jason Sachs (jmsachs_at_[hidden])
Date: 2008-06-23 11:12:56

Ion Gaztañaga <igaztanaga <at> gmail.com> writes:
> 
>        //An allocator convertible to any allocator<T, segment_manager_t> 
> type
>        void_allocator alloc_inst (segment.get_segment_manager());
> 
>        //Construct the shared memory map and fill it
>        complex_map_type *mymap = segment.construct<complex_map_type>
>           //(object name), (first ctor parameter, second ctor parameter)
>              ("MyMap")(std::less<char_string>(), alloc_inst);
> 
>        for(int i = 0; i < 100; ++i){
>           //Both key(string) and value(complex_data) need an allocator 
> in their constructors
>           char_string  key_object(alloc_inst);
>           complex_data mapped_object(i, "default_name", alloc_inst);
>           map_value_type value(key_object, mapped_object);
>           //Modify values and insert them in the map
>           mymap->insert(value);
>        }

Thanks, that helps. I didn't know you could use void_allocators, I thought they
had to be specific for each allocated type. One question: I noticed in the
example you posted, that the lifetime of the allocator "alloc_inst"
equals/exceeds the lifetime of the map and the values that are inserted into the
map. Is this required, or can the allocator just be a temporary stack variable
(as follows)?

    char_string  key_object(void_allocator(segment.get_segment_manager()));