:ptrdiff_t difference_type;
<a name="l00135"></a>00135 
<a name="l00136"></a>00136     <a class="code" href="g_i_l_0576.html" title="function object that returns the memory unit distance between two iterators and advances...">memunit_step_fn</a>(difference_type step=memunit_step(Iterator())) : _step(step) {}
<a name="l00137"></a>00137 
<a name="l00138"></a>00138     difference_type difference(<span class="keyword">const</span> Iterator&amp; it1, <span class="keyword">const</span> Iterator&amp; it2)<span cla