How to pass vector elements by reference in c++?

Question

I have a vector and I need to pass its elements to functions of the type:

bool doIt(MyClass &a);

so I need to do later:

vector<MyClass> v;
doIt(v[2]);

I am not sure if I am doing it right...

Answer 1

I am not sure if I am doing it right...

Yes, you are doing it right, except that in your sample code the vector v does not contain any element, so the index 2 is out-of-bounds, and this expression:

v[2]

Results in undefined behavior. This would be enough to fix it though (if MyClass is default-constructible):

vector<MyClass> v(3);
//                ^
//                Creates a vector of 3 default-constructed 
//                elements of type MyClass
doIt(v[2]);

Answer 2

Let's check the documentation!

http://www.cplusplus.com/reference/vector/vector/operator[]/

reference operator[] (size_type n);
const_reference operator[] (size_type n) const;

Returns a reference to the element at position n in the vector container.

Looks like you're good.