如何将自定义类型（数组）object 推回/复制到向量？

Question

Here is a fragment of my code in which I declare foo:

typedef pair<a, b> foo[8][8];

I wrote a function that copies objects of this type:

copy(foo1, foo2);

will copy foo2 to foo1. foo1 and foo2 are of type foo. Also, I have this vector:

vector<foo> lst;

I would like to have convenient access to it, ie lst [0][0][0].first would be an object of type a. How can I copy a foo object to this vector (lst)? I tried to do it this way:

lst.push_back( new foo );
copy(lst[lst.size() - 1], foo1);

How can I do such a thing?

Answer 1

std::vector<foo> means "vector of foo values", you can't push_back(new foo) into it as new foo is a pointer ( foo* ). You'd need to push_back(foo{}) which default-constructs a foo instance (a value). This doesn't work because:

• std::vector<T>::push_back requires that T is MoveInsertable (in this particular case)
• foo is a C-array, and C-arrays are not MoveInsertable

In general, C-arrays don't work well with std::vector . You can use std::array instead, because it is MoveInsertable .

#include <vector>
#include <array>
#include <iostream>

using foo = std::array<std::array<std::pair<float, float>, 8>, 8>;

std::vector<foo> v;
v.push_back(foo{});
std::cout << v[0][0][0].first << "\n";

In this case you don't need your copy function as std::array will do copying

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