Question

I try to reuse an STL iterator, but cannot find any info about this. Got problem in this code:

    std::vector< boost::shared_ptr<Connection> >::iterator poolbegin = pool.begin();
std::vector< boost::shared_ptr<Connection> >::iterator poolend = pool.end();
if( order ) {
    poolbegin = pool.rbegin(); // Here compilation fails
    poolend   = pool.rend();
}
    for( std::vector< boost::shared_ptr<Connection> >::iterator it = poolbegin; it<poolend; it++) {

But getting error:

error: no match for ‘operator=’ in ‘poolbegin = std::vector<_Tp,
_Alloc>::rbegin() with _Tp = boost::shared_ptr, _Alloc = std::allocator >’

Is there a way to reset iterator to new value? Like shared_ptr::reset ?

Answer 1

It looks like you want to have a loop that goes forward or backward through a vector, depending on some condition.

One way to do this is to factor out the loop body into a functor (or lambda if you have C++11).

struct LoopBody {
  void operator()(boost::shared_ptr<Connection> connection) {
    // do something with the connection
  }
  // If the loop body needs to be stateful, you can add a constructor
  // that sets the initial state in member variables.
};

Now you can have two alternatives for which way you want to go through the loop:

LoopBody loop_body;
if (reverse_order) {
  std::for_each(pool.rbegin(), pool.rend(), loop_body);
} else {
  std::for_each(pool.begin(), pool.end(), loop_body);
}