不需要时进行静态初始化

Question

Quote from 3.6.2/3 of N3797 C++14 final working draft:

An implementation is permitted to perform the initialization of a non-local variable with static storage duration as a static initialization even if such initialization is not required to be done statically, provided that

— the dynamic version of the initialization does not change the value of any other object of namespace scope prior to its initialization, and

— the static version of the initialization produces the same value in the initialized variable as would be produced by the dynamic initialization if all variables not required to be initialized statically were initialized dynamically.

What does all variable have to initialization of one specific variable?

If it possible, describe the latter point by example.

Answer 1

This matters when the initialiser of one variable refers to another variable.

constexpr int f(int);

extern const int a = f(1); // not required to be statically initialized
extern const int b = a; // also not required to be statically initialized

constexpr int f(int x) { return x; }

Now suppose that the implementation chooses to statically initialize b , but dynamically initialize a . In that case, the initialization of b would take place before that of a . The text you ask about explains that this doesn't permit an implementation to initialize b to zero: even if b is initialized first, its value must be f(1) , which is 1 .