CODEWITHSUNDEEP
c++arrayspointersunique-ptr
user5618793
user5618793

Reputation: 141

C++ unique_ptr and arrays

I'm trying to use arrays with unique_ptr with no success.
What is the correct way to declare a unique_ptr of some size?
(size is some paramter).

unique_ptr<A[]> ptr = make_unique<A[]>(size);

Here's an example: 

#include <iostream>  
#include <string>  
#include <vector>
#include <functional>
#include <memory>

using namespace std;

class A {
    string str;
public:
    A(string _str): str(_str) {}
    string getStr() {
        return str;
    }
};

int main()
{
    unique_ptr<A[]> ptr = make_unique<A[]>(3);
}

This is not working, however, if I delete the constructor of A, it works.
I want the 3 to represent the size of the array, and not an argument to A's constructor, how do I make that happen?

Upvotes: 1

Views: 3687

Answers (1)

WhiZTiM
WhiZTiM

Reputation: 21576

This is not working, however, if I delete the constructor of A, it works.

When you removed the user defined constructor, the compiler implicitly generates a default one. When you provide a user defined constructor, the compiler doesn't implicitly generate a default constructor.

std::make_unique<T[]> requires the use of default constructors...

So, provide one, and all should work well

#include <iostream>  
#include <string>  
#include <vector>
#include <functional>
#include <memory>

using namespace std;

class A {
    string str;
public:
    A() = default;
    A(string _str): str(_str) {}
    string getStr() {
        return str;
    }
};

int main()
{
    unique_ptr<A[]> ptr = make_unique<A[]>(3);
}

Upvotes: 3

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