c++ - Move constructor and pre-increment vs post-increment -

in c++, if have loop "copies" objects of user defined type using move constructor, make difference if use ++i or i++ loop counter?

i know question seems rather vague, (i believe) asked in phone interview. wasn't sure if understood question correctly, , interviewer took not knowing answer, , cut interview short.

what have been getting at?

in c++, if have loop "copies" objects of user defined type using move constructor [...]

first of all, move constructor used move-constructing, means not "copying": can realize moving copying - in fact, class copy-constructible move-constructible - why defining move constructor explicitly?

[...] make difference if use ++i or i++ loop counter?

it depends on i is. if scalar object, int, there no difference @ all.

if i class-type iterator, on other hand, ++i should more efficient (on purely theoretical ground), because implementation of operator ++ not have create copy of iterator returned before iterator incremented.

here, instance, how stdlibc++ defines increment operators iterator type of std::list:

_self& operator++() {     _m_node = _m_node->_m_next;     return *this; }  _self operator++(int) {     _self __tmp = *this;     _m_node = _m_node->_m_next;     return __tmp; } 

as can see, postfix version (the 1 accepting dummy int) has more work do: needs create copy of original iterator refurned, alter iterator's internal pointer, return copy.

on other hand, prefix version has alter internal pointer , return (a reference to) itself.

however, please keep in mind when performance concerned, assumptions have backed measurement. in case, not expect sensible difference between these 2 functions.