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7 - Coordinating Objects
Creating a new object means adding itself to this list: cpaRadioButton::cpaRadioButton(int id,
int width,
int height,
const char *caption,
int groupId)
: CRadioButton(id,width,height,caption),
m_tag(-1),
m_groupId(groupId)
{
// add entry to list - simply place at beginning,
// and move curr. pointer to us
m_nextObject =s_firstObject;
s_firstObject=this;
}
Creation is fast because we can add our object
to the start of the list. Deletion is slower,
since we have to walk the list to find our
object pointer first, and then splice the
list to bypass ourselves: cpaRadioButton::~cpaRadioButton(void)
{
// remove itself from chain - walk along
// list, looking for us, then swap out
cpaRadioButton *ptr=s_firstObject;
if ( this==ptr ) // we are first entry?
s_firstObject=m_nextObject; // remove our link
else // unlink from elsewhere
{
while ( NULL!=ptr )
{
if ( this == ptr->m_nextObject )
{
ptr->m_nextObject=m_nextObject;
break;
}
ptr=ptr->m_nextObject;
}
}
}
Walking a sequential list can appear extremely
time-consuming, but before rewriting this
code to use a more efficient algorithm, remember
that there are not likely to be many cpaRadioButtons
at any given time in your program, so you
may be optimizing code that won't benefit
significantly from it.
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