C++ initialization list and constructor

Question

C++14 provides the initialization list and we can use it to initialize elements in a class or struct. What are the differences of the two initialization manners in the following code?

struct MyItem {
  MyItem() : val{0} {}
  int val;
};

struct MyItem {
  MyItem() {}
  int val{0};
};

Answer 1

In your case, there is no difference. The first case uses a mem-initializer to initialize val . The second uses a brace-or-equal-initializer . A brace-or-equal-initializer will be used for a member when there is no mem-initializer present for that member. If there is a mem-initializer , it takes precedence, and the brace-or-equal-initializer is ignored.

One can certainly construct contrived examples where there is a difference...

const int i = 42;

struct S1 {
    S1(int i): val{i} {} // sets val to the parameter i
    int val;
};

struct S2 {
    S2(int i) {} // param is ignored
    int val{i}; // sets val to 42
};