C++: When (and how) are C++ Global Static Constructors Called?

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When talking about non-local static objects there are not many guarantees. As you already know (and it’s also been mentioned here), it should not write code that depends on that. The static initialization order fiasco…

Static objects goes through a two-phase initialization: static initialization and dynamic initialization. The former happens first and performs zero-initialization or initialization by constant expressions. The latter happens after all static initialization is done. This is when constructors are called, for example.

In general, this initialization happens at some time before main(). However, as opposed to what many people think even that is not guaranteed by the C++ standard. What is in fact guaranteed is that the initialization is done before the use of any function or object defined in the same translation unit as the object being initialized. Notice that this is not OS specific. This is C++ rules. Here’s a quote from the Standard:

It is implementation-defined whether or not the dynamic initialization (8.5, 9.4, 12.1, 12.6.1) of an object of
namespace scope is done before the first statement of main. If the initialization is deferred to some point
in time after the first statement of main, it shall occur before the first use of any function or object defined
in the same translation unit as the object to be initialized

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