C++: Constructor versus initializer list in struct/class

问题

An object of a struct/class (that has no constructor) can be created using an initializer list. Why is this not allowed on struct/class with constructor?

struct r { int a; };
struct s { int a; s() : a(0) {} };
r = { 1 }; // works
s = { 1 }; // does not work

回答1:

No, an object with a constructor is no longer considered a POD (plain old data). Objects must only contain other POD types as non-static members (including basic types). A POD can have static functions and static complex data members.

Note that the upcoming C++ standard will allow you to define initializer lists, which will allow non-POD objects to be initialized with braces.

回答2:

If by your question you mean to ask, "Can I do this:"

struct MyGizmo
{
  char things_[5];
  MyGizmo() : things_({'a', 'b', 'c', 'd', 'e'}) ();
};

...then the answer is no. C++ doesn't allow this.

来源：https://stackoverflow.com/questions/2095759/c-constructor-versus-initializer-list-in-struct-class