CODEWITHSUNDEEP
c++
bex91
bex91

Reputation: 123

Can't understand this vector declaration

I'm a real noob in C++ and I've a very simple question.

vector<int> s[10];

What does this declaration actually do? Is s a vector with capacity for 10 integers? What's the difference comparing to this:

vector<int> s(10);

I'm really sorry if this is a stupid question, but I really can't understand what this declarations do.

Thanks!

Upvotes: 3

Views: 145

Answers (4)

Bing
Bing

Reputation: 86

vector<int> s[10];Means "s" is a array, and it have 10 elements, each of its element's type is vector<int>.

vector<int> s(10);Means "s" is a vector<int>, and this vector's size is 10, but this is not a declaration.

There can be much more complex declarations, when declare a function pointer which point to the kind function who have a lot of parameters and complex return value.

For example:

vector<int> (*func[10])(int *); This declare the pointer point to a function who receive int * parameter, and return avector<int> value, plus it is an array of this kind pointer, the size of the array is 10.

Upvotes: 0

JeromeCui
JeromeCui

Reputation: 39

Vector has a constructor like this:

vector (size_type n);

So the second is just declare a vector of int with size of 10.

Upvotes: 0

Dave
Dave

Reputation: 46249

It is a mix of std::vector and built-in array types. Specifically an array of std::vector;

vector<int> s[10];

means create 10 vector objects. You can think of it like:

vector<int> s0;
vector<int> s1;
...
vector<int> s10;

The number of vector objects is fixed. The number of items in each vector can vary.

Upvotes: 2

paddy
paddy

Reputation: 63451

The first one is an array of 10 empty vectors.

The second one is a single vector initialised with 10 elements.

Upvotes: 10

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