Re: STL - erasing from a set

=?windows-1252?Q?Daniel_Kr=FCgler?= <>
Fri, 19 Nov 2010 14:01:45 CST
On 11/19/2010 08:14, Andrey wrote:

You said,

This basically means you would need a
temporary container and it does not remove the mentioned elements from
the source set.

I understand that, but the problem is that this temporary container
cannot be a new (empty) set... it needs to be something that is filled
to the necessary capacity already. I wrote another sample program to
see if I could I could get set_symmetric_difference to work:


using namespace std;

int main() {

     set<int> set_int;

     set<int> set2_int;

     set<int> set_diff;

     set_symmetric_difference(set_int.begin(), set_int.end(),
set2_int.begin(), set2_int.end(), set_diff.begin());

     return 0;

of course, this fails with

[compiler curses omitted]

This is understandable, because

a) the iterator of set are const iterators.
b) there is no memory yet to insert (This means the compile time error
prevents a nasty runtime error here)

Just use an insert iterator adaptor like so for your last line:

std::set_symmetric_difference(set_int.begin(), set_int.end(),
      set2_int.begin(), set2_int.end(),
      std::inserter(set_diff, set_diff.begin()));

Of course, I could use std::set::erase to erase each value
individually, as you mention. But that means I would have to create a
loop. I thought there should be a way to do this in STL in a single

With a C++0x-capable compiler you can write a single line:

std::for_each(set2_int.begin(), set2_int.end(),
      [&](const std::set<int>::value_type& r) { set_int.erase(r); });

HTH & Greetings from Bremen,

Daniel Kr?gler

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