当我尝试打印矢量的内容时，编译器出现错误？

Question

Basically, I have a .h file, in which I have defined a function to generate an element buffer and squashed list of vertices (for OpenGL) given an unoptimized list of vertices. I ran into some problems though, and it turns out that I can't actually access the contents of a vector which I pass to the method. My code is as follows

#ifndef LEARNOPENGL_COMMON_H
#define LEARNOPENGL_COMMON_H

#include "ContextBase.h" // this includes all the OpenGL stuff
#include "vector"
#include "iostream"

class common {
public:

    template<typename V>
    static bool are_equal(int size, V* v1, V* v2) {
        for (int x = 0; x < size; x++) {
            //if (v1[x] != v2[x]) return false;
        }
        return true;
    }

    template<typename V, typename E>
    static void GenOptimizedArrays(const int vertex_size, std::vector<V>* vertex_source,
                                   std::vector<V>* vertex_out, std::vector<E>* ebo_out) {

        std::vector<V> * vertex_vector = new std::vector<V>();
        std::vector<E> * element_vector = new std::vector<E>();

        std::cout << vertex_source[0] << std::endl;
    }
};

#endif //LEARNOPENGL_COMMON_H

However, my compiler is telling me that trying to print (access?) vertex_source[0] is causing an error- the exact (relevant) error message is

error: cannot bind ‘std::ostream {aka std::basic_ostream<char>}
’ lvalue to ‘std::basic_ostream<char>&&

I tried to search this online but, while I found similar problems, everything just said to use an iterator without explaining why I figured out how from the solutions, but found no good explanation. Can you help on this?

Answer 1

std::vector<int> *vec = new vector<int>;
//std::cout<<vec[0];(1)
std::cout<<&vec[0];(2)

If you uncomment (1) and run above snippet you will get almost same error. Variable vec knows only about its address unless you assign data into its pointer location. So when you try to access the data from its pointer location system can't bind it with stream.

If you try to print the address as shown in(2) it will print the address of the location variable vec knows.