Re: [Boost-users] Question regarding mem_fn or function

From: Elisha Berns (e.berns_at_[hidden])
Date: 2005-06-16 21:57:43

Thanks,

That did it.

Elisha

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] [mailto:boost-users-
> bounces_at_[hidden]] On Behalf Of Peter Dimov
> Sent: Thursday, June 16, 2005 6:15 PM
> To: boost-users_at_[hidden]
> Subject: Re: [Boost-users] Question regarding mem_fn or function
> 
> Elisha Berns wrote:
> > Here is a short example, that of course doesn't do anything
important:
> >
> > class X
> > {
> > public:
> > X() {}
> > ~X() {}
> >
> > std::vector< int > vecInteger;
> >
> > bool Sort(int const& lhs, int const& rhs)
> > {
> > return lhs < rhs;
> > }
> > };
> >
> > // then either outside the body of the class:
> >
> > X x;
> >
> > // or inside some other class method you want to sort the vector...
> >
> > // and here's the part that I don't see...
> >
> > std::sort(x.vecInteger.begin(); x.vecInteger.end(),
> > boost::mem_fn(X::Sort));
> 
> mem_fn(&X::Sort) essentially creates the equivalent of the following
> function:
> 
> bool mem_fn_sort( X * this_, int const & lhs, int const & rhs )
> {
>     return this_->Sort( lhs, rhs );
> }
> 
> Since X::Sort is a member function, it needs to operate on an object
of
> type
> X, which explains the additional argument.
> 
> std::sort needs a two-argument predicate, so assuming that you need to
> invoke Sort on your original x, you should write
> 
> std::sort( x.vecInteger.begin(), x.vecInteger.end(),
>     boost::bind( &X::Sort, &x, _1, _2 )
> );
> 
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