I'm using the following code in some cases:
#define array_key_exists(find_key, arr) (arr.find(find_key) != arr.end())
But i also use simply this method:
if(SomeMap["something"]){
// key exists
}
I am using String to int map.
Are they both as fast...? Or is there a possibility for errors with the second case, assuming i am not using zero value in the map values at all? So far the second case seems to work just fine.
The second if-statement will always be entered, because if the key doesn't exist it will be created. (After which, subsequent calls will just return the existing element.)
If you want to find a value and use it if it exists, you typically do this:
std::map<T>::iterator iter = theMap.find(theKey);
if (iter != theMap.end())
{
// use iter
}
else
{
// value doesn't exist
}
If you simply want to know if it's in there, without using it, do:
if (theMap.count(theKey)) // in map, count will return either 0 or 1
{
// it exists
}
else
{
// it doesn't exist
}
At the very least, don't use a macro! There's no reason to in C++:
template <typename Map, typename Key>
bool contains(const Map& pMap, const Key& pKey)
{
return pMap.find(pKey) != pMap.end();
}
But there's no use for this, just use count.
map, count will literally just do: return find(key) != end();.Use find and compare against end iterator like the first method. The second method will insert an empty element into the map if the key didn't exist.
operator[] is: "get element and return it". It isn't for checking if an element is there.if(SomeMap["something"] != NULL){
// key exists
}
Assuming that you do not add any NULL items to the map
NULL is 0. If there are valid elements that compare to 0 then this is broken.