Updating element in an STL set<>
Greetings,
I am using a set<> of classes, where one or more members of the structure are used to determine sorting order. But not all members. This happens to work out very nicely when I have have to maintain a table for SNMP--I just define operator<() to be the SNMP ordering function. All that works just fine.
However, I find that when I need to update an element of the set (not the indices used by operator<) I cannot as I get a const reference or iterator. Fine, that's the way set<> works, by assuming that all parts of the type are used in the sorting function. But it means that doing an update of an existing element is awkward; I must remove the original entry and then insert a new one to replace it. And these 2 versions have exactly the same indices.
Below is a trimmed down version of the class and an update function. It works, but it just seems like it is unreasonably inefficient to have to:
- Find if there is an existing element already
- Remove that element
- Insert a new element that winds up in exactly the same position!
So, finally, my question is: Is there a standard paradigm for updating a member of a set<>?
Code:
class ENTPHYSICALENTRY : public PHYSICAL_ENTITY_STRUCT
{
public:
ENTPHYSICALENTRY(void) // default constructor
{
initEmptyEntry();
}
~ENTPHYSICALENTRY(void) {}
void initEmptyEntry(void);
ENTPHYSICALENTRY(const PHYSICAL_ENTITY_STRUCT &t)
{
CopyModule(&t);
}
ENTPHYSICALENTRY & operator= (const ENTPHYSICALENTRY &t)
{
if(&t != this) // avoid copying to one's self
{
CopyModule(&t);
}
return(*this);
}
void CopyModule(const PHYSICAL_ENTITY_STRUCT *t);
bool operator< (const ENTPHYSICALENTRY &r) const
{
if(this->entPhysicalIndex < r.entPhysicalIndex)
return(true);
return(false);
}
};
typedef std::set<ENTPHYSICALENTRY> ENTPHYSICALSET;
typedef ENTPHYSICALSET::iterator ENTPHYSICALITER;
ENTPHYSICALSET entPhysicalTable; // This is the actual table of entPhysicalEntry
// Insert new entry or replace old entry with more recent version
STATUS UpdateEntityEntry(ENTPHYSICALENTRY &entry)
{
// insert() will not overwrite, so we must remove and insert if it already exists.
// And erase() crashes if the entry doesn't already exist.
ENTPHYSICALITER iter = entPhysicalTable.find(entry);
if(iter != entPhysicalTable.end())
{
(void)entPhysicalTable.erase(iter);
}
pair<ENTPHYSICALITER, bool> insertRetval = entPhysicalTable.insert(entry);
if(ASSERT(insertRetval.second)) // second is a bool which is true if the insert succeeded
{
return ERROR;
}
blah, blah, blah, ...
}
I suspect I am just missing something. Suggestions appreciated.
Thanks.
-- Harold
