Is there support in C++/STL for sorting objects by attribute?

Question

I wonder if there is support in STL for this:

Say I have an class like this :

class Person
{
public:
  int getAge() const;
  double getIncome() const         


        

Answer 1

Generic adaptor to compare based on member attributes. While it is quite more verbose the first time it is reusable.

// Generic member less than
template 
struct member_lt_type 
{
   typedef M T::* member_ptr;
   member_lt_type( member_ptr p, C c ) : ptr(p), cmp(c) {}
   bool operator()( T const & lhs, T const & rhs ) const 
   {
      return cmp( lhs.*ptr, rhs.*ptr );
   }
   member_ptr ptr;
   C cmp;
};

// dereference adaptor
template 
struct dereferrer
{
   dereferrer( C cmp ) : cmp(cmp) {}
   bool operator()( T * lhs, T * rhs ) const {
      return cmp( *lhs, *rhs );
   }
   C cmp;
};

// syntactic sugar
template 
member_lt_type > member_lt( M T::*ptr ) {
   return member_lt_type >(ptr, std::less() );
}

template 
member_lt_type member_lt( M T::*ptr, C cmp ) {
   return member_lt_type( ptr, cmp );
}

template 
dereferrer deref( C cmp ) {
   return dereferrer( cmp );
}

// usage:    
struct test { int x; }
int main() {
   std::vector v;
   std::sort( v.begin(), v.end(), member_lt( &test::x ) );
   std::sort( v.begin(), v.end(), member_lt( &test::x, std::greater() ) );

   std::vector vp;
   std::sort( v.begin(), v.end(), deref( member_lt( &test::x ) ) );
}