I have this simple class:
class MyClass {
public:
int id;
string name;
};
I want to have a vector with pointers to objects of this class that is sorted by the referenced MyClass id. I thought that using lower_bound would be easy, I did it before with vectors of objects (not pointers). With objects, I overloaded operator< like that:
bool operator<(MyClass left, int right) {
return (left.id < right);
}
Then I used lower_bound to insert new MyClass object to sorted vector.
vector<MyClass>::iterator low;
low = lower_bound(vectorname.begin(),vectorname.end(),id);
prP = idContainer.begin();
prP = idContainer.insert(low, newobject);
I am lost how to do the same with the vector of MyClass pointers. Can anyone help me achieve that?
There are two overloads of std::lower_bound:
template< class ForwardIt, class T >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value );
template< class ForwardIt, class T, class Compare >
ForwardIt lower_bound( ForwardIt first, ForwardIt last, const T& value, Compare comp );
The first one is the one you used for your vector<MyClass>, it uses operator< by default. The second one allows for a custom comparison function which takes an element from the container as the first argument and the value as the second. That's what you want to use for your vector<MyClass*>:
std::vector<MyClass*> pvec;
auto low = std::lower_bound(pvec.begin(), pvec.end(), id,
[](const MyClass* c, const MyClass& id) {
return *c < id;
});
It's a little odd that the comparison takes two arguments of different types, but that's just how it is.
Note: your current operator< takes its arguments by value. That incurs unnecessary copies. You'll want to change that to take them by reference to const.
