Re: stl::map: return default value without inserting a new element?
Christian Hackl wrote:
But shouldn't you rather view it as an error to access an element which
does not exist?
Not necessarily. In this case it would be nice if it behaved just as operator[] minus the
new key:value insertion, which means returning the value if a key:value pair was found and
otherwise return a default value.
Perhaps what you should do is access elements with a
function like this:
template <class KeyType, class MappedType>
MappedType const &get(std::map<KeyType, MappedType> const &map, KeyType
const &key)
{
std::map<KeyType, MappedType>::const_iterator find_iter =
map.find(key);
assert(find_iter != map.end());
return find_iter->second;
}
(Note how this, in contrast to operator[], can be used with a const
std::map as well.)
That's not quite it. I was looking for a STL way to do something such as:
<source lang=cpp>
template <class KeyType, class MappedType>
MappedType const &get(std::map<KeyType, MappedType> const &map, KeyType
const &key)
{
std::map<KeyType, MappedType>::const_iterator find_iter =
map.find(key);
if(find_iter == map.end())
return MappedType();
else
return find_iter->second;
}
</source>
Then make sure outside code accesses only those elements which exist. It
seems a more robust solution to me than relying on default values being
returned in case the key does not exist. Otherwise, what happens when
the default value happens to be one of the actual values in the map?
In my case there's no problem with that.
You
won't be able to distinguish between legitimate access and error cases.
In my case those aren't errors, which means this is a non-issue.
Rui Maciel