Re: [Libcds-user] Retrieve value with MichaelHashMap

[Max K. <kh...@gm...>]

Suppose, your container maps int to struct Foo:

struct Foo {
     my_rw_lock    lock   ;    //  access lock of some r/w type
     std::string       str     ;
};

typedef cds::container::MichaelHashMap< ... > map_type ;

map_type myMap ;
...

How to apply functor:

struct my_func {
     std::string strFound ;
     void operator()( map_type::value_type& val )
     {
         val.lock.lock_read()    ;
         strFound = val.str ;
         val.lock.unlock_read() ;
     }
};

my_func f ;
if ( myMap.find( 5, cds::ref(f)) ) {
     std::cout << "Value for 5 = " << f.strFound ;
}
else
     std::cout << "Not found" ;

In this code cds::ref (or boost::ref) is needed for passing functor by 
reference
since the functor contains data.

or, if your compiler supports C++11 lambda:

std::string strFound ;
if ( myMap.find( 5, [&strFound]( map_type::value_type& val) {
         val.lock.lock_read()   ;
         strFound = val.str     ;
         val.lock.unlock_read() ;
    } ) )
{
     std::cout << "Value for 5 = " << f.strFound ;
}
else
     std::cout << "Not found" ;

BR
     Max Khiszinsky

On 01/30/2013 05:26 PM, Lucas Lersch wrote:
> I am using MichaelHashMap following the example in the documentation 
> (http://libcds.sourceforge.net/doc/cds-api/classcds_1_1container_1_1_michael_hash_map.html#details). 
> I see I can pass a functor as argument to the find() method to 
> manipulate the <key,value> pair found. My problem is that I am having 
> problems to define such functor and to pass it as argument to the 
> find() method.
>
> Can someone provide me a simple example on how to retrieve a value 
> from the MichaelHashMap from a key, following the existing example in 
> the documentation?
>
> Thank you for the attention. :)
>
> -- 
> Lucas Lersch
>
>
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