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

17 Jun 2005

      Thanks,

That did it.

Elisha
...
-----Original Message-----
From: boost-users-bounces@lists.boost.org [mailto:boost-users-
bounces@lists.boost.org] On Behalf Of Peter Dimov
Sent: Thursday, June 16, 2005 6:15 PM
To: boost-users@lists.boost.org
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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