I just discovered that the problem may be something totally different than it appears. The following code compiles and works just fine but Intellisense tells me that v1(10) is not valid and that v1.size() is not legal, stating that they are both unknown constructors.
I guess I must now pursue why my Intellisense is broken.
#include <iostream>
#include <vector>
using namespace std;
int main()
{
vector<int> v1(10);
int x = v1.size();
}
Fixed my problem by deleting the .suo file in the Solution folder. Apparently this file is used for Intellisense caching. Deleting it seems to have resolved the problem. Sorry for leading everyone down a rabbit hole.