What is different between these two vectors? (smart pointers)

Question

3.00/5 (1 vote)

See more:

I am learning about smart pointers.

C++

class Elf {
private:
    int _health = 0;
public:
    Elf(const int &health){_health = health;}
    int getHealth(){return _health}
};

What is the different between these two?
First case:

C++

vector<unique_ptr<Elf>> elves;
for (auto i = 0; i < 10000; ++i) {
    elves.push_back(unique_ptr<Elf>(new Elf(90)));
}

Second case:

C++

auto elves = make_unique<vector<Elf>>(10000, Elf(90));

=========
The second question.
For the first case, I can access private member _health by this:

C++

for(auto i = 0; i < 10000; ++i){
    cout << elves[i]->getHealth() << " ";
}

How to access _health in the second case?

Posted 15-Dec-15 6:59am

Are Riff

Updated 5-Apr-17 5:18am

Add a Solution

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Stefan_Lang · Answer 1 · 2017-04-05T05:18:00

Quote:
What is the different between these two?

The first is a vector of (smart) pointers to elves and the second is a (smart) pointer to a vector of actual elves.

You could compare the first to a sign pointing to a chest of drawers with an elf sitting in each drawer (basically a large house), whereas the second is a chest of drawers where each drawer contains the home address of an elf (basically an address book).

Quote:
How to access _health in the second case?

Solution 1 should work, but if you prefer code that uses the index operator (and thus is closer to the first version), try this:

C++

cout << (*elves)[i].getHealth();

P.S.:
oops, just noticed the date. I assumed it was a new request based on it's listing on the front page...

Theo Buys · Answer 2 · 2017-04-05T00:36:00

Solution 1

#include <memory>
#include <vector>


class Elf {
private:
	int _health = 0;
public:
	Elf(const int &health){ _health = health; }
	int getHealth(){ return _health; }
};


void Test()
{
	using namespace std;
	auto elves = make_unique<vector<Elf>>(10000, Elf(90));

	int out;
	for (auto i = 0; i < 10000; i++)
	{
		out = elves->at(i).getHealth(); /* out = 90 */
	}	

}

Posted 5-Apr-17 0:36am

Theo Buys

Updated 5-Apr-17 0:45am

v4

Comments

Dave Kreskowiak 5-Apr-17 9:39am

Watch the dates on posts. This is a year and a half old.

Theo Buys 5-Apr-17 11:20am

Time is on my side. Why nobody has aswerwerd this nice question?