C++ inserting unique_ptr in map

Question

I have a C++ object of type ObjectArray

typedef map<int64_t, std::unique_ptr<Class1>> ObjectArray;

What is the syntax to create a unique_ptr to a new object of type Class1 and insert it into an object of type ObjectArray?

Solution 1

As a first remark, I wouldn't call it ObjectArray if it is a map and not an array.

Anyway, you can insert objects this way:

ObjectArray myMap;
myMap.insert(std::make_pair(0, std::unique_ptr<Class1>(new Class1())));

Or this way:

ObjectArray myMap;
myMap[0] = std::unique_ptr<Class1>(new Class1());

The difference between the two forms is that the former will fail if the key 0 is already present in the map, while the second one will overwrite its value with the new one.

In C++14, you may want to use std::make_unique() instead of constructing the unique_ptr from a new expression. For instance:

myMap[0] = std::make_unique<Class1>();

Solution 2

If you want to add an existing pointer to insert into the map, you will have to use std::move.

For example:

std::unique_ptr<Class1> classPtr(new Class1);

myMap.insert(std::make_pair(0,std::move(classPtr)));

Solution 3

In addition to previous answers, I wanted to point out that there is also a method emplace (it's convenient when you cannot/don't want to make a copy), so you can write it like this:

ObjectArray object_array;
auto pointer = std::make_unique<Class1>(...);  // since C++14
object_array.emplace(239LL, std::move(pointer));
// You can also inline unique pointer:
object_array.emplace(30LL, std::make_unique<Class1>(...));