Re: [Boost-users] [boost-users][multi-index] subtracting containers

Hi Joaquín, Thank you very much for your response. Have a nice vacation!

Hi Igor,

Excuse my late answering, I'm away on vacation and with little access to Internet. Your problem is not particualrly related to Boost.MultiIndex, since it is entirely analogous to the same issue as posed with std::sets. You can use std::set_difference, but the interface of this function forces you yo create a fresh copy with the result of the difference rather than doing the subtraction in place. Another alternative would be to use std::for_each more or less like this:

typedef multi_index_container multi_t;

struct multi_t_erase { multi_t_erase(multi_t& m):pm(&pm){} void operator()(int n){pm->erase(n);}

private: multi_t* pm; };

std::for_each(c2.begin(),c2.end(),multi_t_erase(c1));

Yet another alternative consists in traversing both containers more or less in the same way as std::set_difference does:

multi_t::iterator f1=c1.begin(),l1=c1.end(),f2=c2.begin(),l2=c2.end(); while(f1!=l1&&f2!=l2){ if(c1.value_comp()(*f1,*f2))c1.erase(f1++); else if(c1.value_comp()(*f2,*f1))++f2; else ++f1,++f2; } c1.erase(f1,l1);