Question

void spawn_enemies(vector<Enemy>& enemies) {

I had that function, and it worked just fine to pass a vector of Enemy’s as an argument.

However, I know have a vector of <Enemy*>‘s, and it doesn’t work so well, and I also tried to use:

void spawn_enemies(vector<Enemy*>& enemies) {

But it didn’t work either, I get the following error on compilation:

src/Paxlure.cpp:32:28: error: no matching function for call to ‘std::vector<Enemy*>::push_back(Enemy&)’
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/bits/stl_vector.h:826:7: note: void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = Enemy*, _Alloc = std::allocator<Enemy*>, std::vector<_Tp, _Alloc>::value_type = Enemy*]
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.6.2/../../../../include/c++/4.6.2/bits/stl_vector.h:826:7: note:   no known conversion for argument 1 from ‘Enemy’ to ‘Enemy* const&’

Thank you

Answer 1

If you have a vector of pointers, you need to push_back pointers, not objects.

vector<Enemy> enemies;
Enemy e;
enemies.push_back(e);

versus

vector<Enemy*> enemies;
Enemy* pe = new Enemy;
enemies.push_back(pe);

In the latter case, with dynamically allocated memory, you’ll need to free it yourself: delete pe;. But you have to make sure you correctly manage the memory – don’t delete it before you’re sure the vector will no longer try to work with it. Or simply use smart pointers instead of raw ones.