Difference in default initialization of struct members

Question

struct Date1 {
  int day{1};
  int month{1};
  int year{2000};
};
struct Date2 {
  int day  =1;
  int month =1;
  int year =2000;
};
struct Date3 {
  Date() : day(1), month(1), year(2000) {}
  int day;
  int month;
  int year;
};

Is there any difference in terms of efficiency between those three options of default initialization of the struct member?

Answer 1

Is there any difference in terms of efficiency between those three options of default initialization of the struct member?

No. In class member initializers are just syntactic sugar for a member initialization list so they all generate the same code.

The real benefit comes from when you have multiple constructors like

struct Date {
  int day{1};
  int month{1};
  int year{2000};
  Date(int year) : year(year) {}
  Date(int year, int month) : year(year), month(month) {}
  Date(int year, int month, int day) : year(year), month(month), day(day) {}
};

versus

struct Date {
  int day;
  int month;
  int year;
  Date(int year) : year(year), month(1), day(1) {}
  Date(int year, int month) : year(year), month(month), day(1) {}
  Date(int year, int month, int day) : year(year), month(month), day(day) {}
};

In the first case if I need to change the default day, I only need to change it in once. In the second code block I have to update it twice, so it's more work and with more work comes more chances for getting it wrong.