is iterator initialization inside loop deliberate bad style, why?

typically stl formula this:

for (someclass::somecontainer::iterator iter = m_somemembercontainervar.begin(); iter != m_somemembercontainervar.end(); ++iter)
{
}

but indeed have recommendation this:

someclass::somecontainer::iterator iter = m_somemembercontainervar.begin();
someclass::somecontainer::iterator iterend = m_somemembercontainervar.end();
for (; iter != iterend; ++iter)
{
}

if you're nervous scoping, supplement enclosing braces:

{
    someclass::somecontainer::iterator iter = m_somemembercontainervar.begin();
    someclass::somecontainer::iterator iterend = m_somemembercontainervar.end();
    (; iter != iterend; ++iter)
    {
    }
}

this ostensible give speed potency gain, generally programming consoles, since .end() duty called any iteration loop. i only take opening alleviation granted, sounds reasonable nonetheless i don't know many definitely depends form enclosing tangible stl doing use. nonetheless carrying used impression integrate months i indeed move over initial anyway.

the reason being readability: line neat tidy. qualifiers member variables genuine prolongation formula definitely easy have really enlarged lines impression initial example. that's since i intentionally finished have plane scrollbar example, only i'm articulate about. ;)

on hand, astonishing broach iter variables outdoor range loop. nonetheless then, during slightest sourroundings i work in, iter have permitted outdoor range even initial example.

what your take this? there any pro's initial impression presumably confining range iter?