Uniform Initialization with C++11

Initialization of variables types has received a face lift with the new version of the C++ standard. Previously trying to initialize a populated list was impossible and you were left writing helper functions to transform array values into other container types, or worse you’d end up with code that looked like this.

vector<int> i;

// populate the vector
i.push_back(1);
i.push_back(2);
i.push_back(3);
i.push_back(4);

C++11 includes a feature called “Uniform Initialization” which aims to solve this problem. The above code now turns into this.

vector<int> i {1, 2, 3, 4};

Much better. This isn’t where the convenience ends though. Take the following example. Because the person class defines a constructor taking in first_name, last_name and age we are able to use uniform initialization to setup these variables.

// declare the person class
class person {
  public:
    person(void) = default;
    person(const string& fn, const string &ln, const int a) 
      : first_name(fn), last_name(ln), age(a) { }
    virtual ~person(void) = default;

  private:
    string first_name, last_name;
    int age;
};

// initialize a person
person p { "John", "Smith", 25 };

// initialize a vector of people
vector<person> people { {"Mary", "Brown", 21},
                        {"Joe", "Jones", 35},
                        p,
                        {"Sally", "Green", 32} };

The same syntax works with any of the enumerated containers. Using the person class from above, we can make a map of employee records by doing the following.

map<int, person> employees {
  {1, {"Mary", "Brown", 21}},
  {2, {"Joe", "Jones", 35}},
  {3, {"John", "Smith", 25}},
  {4, {"Sally", "Green", 32}}
};

You can see how this syntax makes the initialization process a much more pleasant experience in C++ now. That’s all for this one.