将构造函数传递给指针数组

Question

I have always been using vectors for storing objects when a list type container is required. I wanted to know how you can pass constructors to array pointers.The following works in C++03 if the object foo did not have a constructor

foo* p = new foo[5]()

Now what if the constructor of foo required an int how would I pass the constructor in the above statement?

Answer 1

It is not possible. Your foo instances can only be default-constructed.

UPDATE 1

If your foo does not have a default constructor then you will get a compiler error either about use of deleted function or about no matching ctor.

UPDATE 2

I see that others offer C++11 solution. My answer appears to be correct only for C++03 or earlier.

Answer 2

Since C++11, you can use brace initializers:

foo * p = new foo[5] { 1, 2, 3, 4, 5 };   // better: "auto p = ..."

This assumes that foo is implicitly constructible from int .

But you can just as well use containers:

std::vector<foo> v { 1, 2, 3 };
std::list<foo> w { 1, 2, 3 };

Or perhaps:

std::unique_ptr<foo[]> q(new foo[4] { 1, 2, 3, 4} );

Answer 3

how would I pass the constructor in the above statement?

new[] does not have a form for forwarding constructor parameters.

You would instead call the constructors yourself.

foo* p = new foo[5]{ foo(1), foo(2), foo(3), foo(4), foo(5) };