C ++ traverse objects and get their addresses

Question

I have the following piece of code:

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

triangle

is the class derived from the class shape

, and triangles

is the triangle std::vector

:

std::vector<triangle> triangles;

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

+3

Eutherpy Apr 12 17 at 13:37

2 answers

You get the address of a local temporary variable, change the type x

to auto&

, after which you get a link to vector elements.

+1

Jonas Apr 12 17 at 13:40

Slava · Accepted Answer · 2017-04-12T13:39:56+0000

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);
}

make a copy on each iteration, change your loop to:

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