Question

How to use unique_ptr in C++

Answer 1

#include <iostream>
#include  <memory>

using std::cout;
using std::endl;

struct S
{
	int N;
	S(int i) :N(i)
	{
		cout << "Constructor" << endl;
	}
	~S()
	{
		cout << "Destructor" << endl;
	}
};

int main()
{
	std::unique_ptr<S> UPtr(new S(100));

	int i = UPtr->N;

	cout << i << endl;

	return 0;
}


/*
run:

Constructor
100
Destructor

*/

 

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Answer 2

#include <iostream>
#include  <memory>

using std::cout;
using std::endl;

struct S
{
	int N;
	S(int i) :N(i)
	{
		cout << "Constructor" << endl;
	}
	~S()
	{
		cout << "Destructor" << endl;
	}
};

int main()
{
	std::unique_ptr<S> UPtr(new S(100));

	cout << UPtr->N << endl;

	return 0;
}


/*
run:

Constructor
100
Destructor

*/

 

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Answer 3

#include <iostream>
#include  <memory>

using std::cout;
using std::endl;

struct S
{
	int N;
	S(int i) :N(i)
	{
		cout << "Constructor" << endl;
	}
	~S()
	{
		cout << "Destructor" << endl;
	}
};

int main()
{
	std::unique_ptr<S> UPtr(new S(100));

	UPtr.reset();

	if (UPtr == nullptr)
		cout << "UPtr is  empty" << endl;

	return 0;
}


/*
run:

Constructor
Destructor
UPtr is  empty

*/

 

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Answer 4

#include <iostream>
#include  <memory>

using std::cout;
using std::endl;

struct S
{
	int N;
	S(int i) :N(i)
	{
		cout << "Constructor" << endl;
	}
	~S()
	{
		cout << "Destructor" << endl;
	}
};

int main()
{
	std::unique_ptr<S> UPtr(new S(100));

	std::unique_ptr<S> UPtr2 = std::move(UPtr);

	cout << UPtr2->N << endl;

	return 0;
}


/*
run:

Constructor
100
Destructor

*/

 

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Answer 5

#include <iostream>
#include  <memory>

using std::cout;
using std::endl;

struct S
{
	int N;
	S(int i) :N(i)
	{
		cout << "Constructor" << endl;
	}
	~S()
	{
		cout << "Destructor" << endl;
	}
};

int main()
{
	std::unique_ptr<S> UPtr(new S(100));

	std::unique_ptr<S> UPtr2(new S(333));

	cout << UPtr->N << endl;
	cout << UPtr2->N << endl;

	return 0;
}


/*
run:

Constructor
Constructor
100
333
Destructor
Destructor

*/

 

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Answer 6

#include <iostream>
#include  <memory>

using std::cout;
using std::endl;

struct S
{
	int N;
	S(int i) :N(i)
	{
		cout << "Constructor" << endl;
	}
	~S()
	{
		cout << "Destructor" << endl;
	}
};

int main()
{
	std::unique_ptr<S> UPtr(new S(100));

	S *p = UPtr.release();

	if (UPtr == nullptr)
		cout << "UPtr is empty" << endl;

	cout << p->N << endl;

	delete p;

	return 0;
}


/*
run:

Constructor
UPtr is empty
100
Destructor

*/

 

70+ SQL courses for beginners and professionals