Can I compare vector objects to NULL? - c++

Question

I come from Python/Java land and I'm trying to tinker with making my own hashmap now in c++.
When I try to check to compare the locations of positions in the hash table to NULL (lines 6 and 11), I get the error:
invalid operands to binary expression ('value_type' (aka 'HashEntry') and 'long')"
I'm hoping someone can steer me in the direction of what I'm doing wrong and how I can fix it.
void CustomHash::insert(HashEntry entry) {
int k = entry.getKey();
int i = 0;
int hashVal = hash_One(k);
int temp = hashVal;
while (i < size && hashArray[temp] != NULL) {
i++;
temp = (hashVal + i*hash_Two(k)) % size;
}
if (hashArray[temp] == NULL) {
hashArray[temp] = entry;
}
else {
cout << "Failure" << endl;
}
}
Edit 1: hashArray declaration
CustomHash::CustomHash(int m) {
this->size = m;
this->hashArray = vector<HashEntry>();
}

Answer 1

Given,
hashArray is a vector<HashEntry> Object
hashArray[temp] evaluates to a HashEntry. You cannot compare a HashEntry with NULL.
Use a different strategy to check whether hasArray has any items whose key is equal to temp. I suggest using std::count_if.
while (i < size && std::count_if(hashArray.begin(), hashArray.end(),
[=temp](HashEntry const& e)
{ return (temp == e.getKey());}) > 0 )
{
i++;
temp = (hashVal + i*hash_Two(k)) % size;
}
A better solution, as suggested by #cdhowie, is to use std::any_of.
while (i < size && std::any_of(hashArray.begin(), hashArray.end(),
[=temp](HashEntry const& e)
{ return (temp == e.getKey());}) )
{
i++;
temp = (hashVal + i*hash_Two(k)) % size;
}