How to initialize a vector with an explicit element initializer?

We can use the following syntax to initialize a vector.

// assume that UserType has a default constructor
vector<UserType> vecCollections; 
开发者_高级运维

Now, if UserType doesn't provide a default constructor for UserType but only a constructor as follows:

explicit UserType::UserType(int i) { ... }.

How should I call this explicit element initializer with the vector constructor?

vector<UserType> vecCollections(10, UserType(2));

Unfortunately there is no way in current C++ (C++03) to initialize the vector with arbitrary elemtnts. You can initialize it with one and the same element as in @Erik's answer.

However in C++0x you can do it. It is called an initializer_list

vector<UserType> vecCollections({UserType(1), UserType(5), UserType(10)});

Incidentally, you might want to check out the boost::assign library, which is a very syntactically convenient way to assign to a vector and other containers

std::vector<char> items(10, 'A'); //initialize all 10 elements with 'A'

However, if you want to initialize the vector with different values, then you can write a generic vector initializer class template, and use it everywhere:

template<typename T>
struct initializer
{
   std::vector<T> items;
   initializer(const T & item) { items.push_back(item); }
   initializer& operator()(const T & item) 
   {
      items.push_back(item);
      return *this;
   }
   operator std::vector<T>&() { return items ; }
};

int main() {
        std::vector<int> items(initializer<int>(1)(2)(3)(4)(5));
        for (size_t i = 0 ; i < items.size() ; i++ )
           std::cout << items[i] << std::endl;
        return 0;
}

Output:

1
2
3
4
5

Demo at ideone: http://ideone.com/9dODD