is define code: vector intVector will call default constructor and is same with vector intVector()?

Question

code one:

vector<int> *intVector=new vector<int>();

code two:

vector<int> *intVector=new vector<int>;

code three:

vector<int> intVector();//compile error?

code four:

vector<int> intVector;

my questions:

(1) is "vector intVector" call default constructor?
(2) when code 1 is similar with code 2, why code 3 compiled error?

@NicolBolas, I'm not sure if I should make it as answer or not. This question is **very** popular and it has been asked many times. — awesoon, Apr 13 '13 at 09:25

score 2 · Accepted Answer · answered Apr 13 '13 at 10:16

You ask:

(1) is "vector intVector" call default constructor?
(2) when code 1 is similar with code 2, why code 3 compiled error?

Regarding (1), yes, std::vector has a user-defined default constructor, which is used when no constructor arguments are provided.

Regarding (2), your code 3 shouldn't give an error of itself, but it is a declaration of a function, not a declaration of a variable. So if you're using it as a variable, then you may get compilation errors on that usage.

Your code example 4 is how you should generally use a std::vector. For a number of reasons there is little to no point in allocating a std::vector dynamically, with new, and there is a (relatively speaking) huge cost associated with new. So just use a straight std::vector object, and it takes care of memory allocation and deallocation for you.

is define code: vector intVector will call default constructor and is same with vector intVector()?

1 Answers1