C++ loop through objects and obtain their addresses

Question

I have the following code snippet:

vector<shape*> triangle_ptrs;
for (auto x : triangles)
    triangle_ptrs.push_back(&x);

triangle is a class derived from shape class, and triangles is an std::vector of triangles:

std::vector<triangle> triangles;

I need to save the addresses of the triangles, but as I loop through the collection, their addresses seem to be the same. How do I go around this?

Answer 1

In this loop:

for (auto x : triangles)
    triangle_ptrs.push_back(&x);

which is logically equal to:

for ( auto it = triangles.begin(), it != triangles.end(); ++it) { 
    auto x  = *it; 
    triangle_ptrs.push_back(&x);
} 

you make a copy in each iteration, change your loop to:

for (auto &x : triangles)
    triangle_ptrs.push_back(&x);

Answer 2

您将获取本地临时变量的地址，将x的类型更改为auto&然后您将获得对vector元素的引用。