Concept difference between pre and post increment operator for STL

Question

Supposedly:

for (vector::iterator iter = ivec.begin(); iter != ivec.end(); ++iter)
{}

I do understand the difference when it com

Answer 1

It all depends on how they are implemented.

But the most common way implementation of post increment is in terms of pre-increment with an extra copy.

class MyIter
{
    // Definition of pre-increment:
    //    ++object;
    MyIter& operator++()
    {
        /* Increment the iterator as appropriate
           You should be changing the object in place
         */


        // Once you are done return yourself.
        return *this;
    }
    // Definition of post-increment:
    //    object++;
    MyIter operator++(int)
    {
        // Post increment (returns the same value) so build the result.
        MyIter  result(*this);

        // Now do the increment using pre-increment on the current object
        ++(*this);

        // return the result.
        return result;
    }
};

So the standard implementation of post increment calls pre-increment and in addition makes a copy of the object. Note there is also an additional copy construction on return but this is usually illeded by the compiler.

Note pre-increment because it affects the same obejct usually returns a reference to itslef (so not cost on the return).