Re: [Boost-users] [ptr_container] ptr_map predicates

9 Feb 2006

      ...
How would I accomplish the following using ptr_map instead of std::map?
typedef std::map< std::string, int* > stlmap;
bool predicate( stlmap::value_type& mapitem )
{
    // return true if key value has at least 4 characters
    return( mapitem.first.size() > 3 );
}
void sample( stlmap& themap )
{
    std::find_if( themap.begin(), themap.end(), predicate );
}
The predicate for std::find_if requires *iterator for the parameter.
However, with ptr_map *iterator returns a reference to the element value
instead of the key/value pair. Normally this is fine (in general code I
m.begin.base() seems like it might work, but I'm having a little trouble
figuring out the right parameters for the predicate.

bpmap::value_type doesn't match. What's the correct type/typedef to use for
the base void-ptr-map?

Thanks,

-- Bill --

-----Original Message-----
From: boost-users-bounces@lists.boost.org
[mailto:boost-users-bounces@lists.boost.org] On Behalf Of Thorsten Ottosen
Sent: Thursday, February 09, 2006 4:09 AM
To: boost-users@lists.boost.org
Subject: Re: [Boost-users] [ptr_container] ptr_map predicates

Bill Buklis wrote:
like
...
this feature), but in this case I need access to the key in the predicate.
How do I get at it?
this is an interesting use-case that I haven't thought of.
...
ptr_map version of above:
typedef boost::ptr_map< std::string, int > bpmap;
bool predicate( ??? )
{
  ???
}
bool predicate( const std::pair& p )
{
   return p.first.size() > 3;
}
...
void sample( bpmap& themap )
{
    std::find_if( ??? );
}
void sample( bpmap& m )
{
   std::find_if( m.begin().base(), m.end().base(), predicate() );
}

iterator.base() should return an iterator to the underlying void-ptr-map.

I hope it works

-Thorsten

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