C++ inserting unique_ptr in map

c++ pointers map stl unique-ptr
vigs1990 picture vigs1990 · Jun 4, 2013 · Viewed 61k times · Source

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?

Answer

Andy Prowl picture Andy Prowl · Jun 4, 2013

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>();

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