如何从std :: vector <>正确初始化向量

Question

When I compile the following code (using the -std=c++11 compiler flag), I get the (only) error message: " 'vec' is not a class, namespace or enumeration".

#include <vector>
#include <iterator>

int main(){

std::vector<int> vec(10,1);
vec::iterator it;

return 0;
}

As I do not get any other error message, to me this means that some object called 'vec' has been initialized, but not as a vector, but as something else which is not a class and for which the scope operator can therefore not be used.

As far as I understood it, I used the following constructor ( http://en.cppreference.com/w/cpp/container/vector/vector ):

vector(size_type count,
       const T& value,
       const Allocator& alloc = Allocator());

Where it says that this constructor "Constructs the container with count copies of elements with value value", so I expect to have created a vector with 10 copies of "1", but I must have misunderstood something, hence the problem.

Where did my reasoning go wrong and where does the error in the above code stem from?

Answer 1

Your initialization of the vector is fine. But in order to refer to the iterator type, you need to use the vector's type and not an object:

std::vector<int>::iterator it;

Answer 2

The scope operator is used for accessing elements within a namespace or class. vec isn't a class but an object. You have to write std::vector<int>::iterator . You could also deduce a type of a variable by using auto: auto it = vec.begin() equals to std::vector<int>::iterator it = vec.begin()