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TL;DR The initialization of the variables a and b in your question are indeterminately sequenced in relation to each other. The initialization order is not guaranteed between them. The initiali...
Answer
#2: Post edited
by
Lundin
·
2020-11-17T16:00:59Z (almost 4 years ago)
- TL;DR
The variables `a` and `b` in your question are indeterminately sequenced in relation to each other. The initialization order is not guaranteed between them.- ---
- The initialization rules of C++ are quite complex, especially past C++11. The relevant part would be C++11 3.6.2, "Initialization of non-local variables" which speaks of zero initialization, then constant initialization. The formal terms are defined as
- > Together, zero-initialization and constant initialization are called _static initialization_; all other initialization
- is _dynamic initialization_.
- Your specific case sorts under dynamic initialization, even if the storage duration of the objects are static/thread storage. Static storage variables have the following rules, emphasis mine:
- > **Dynamic initialization of a non-local variable with static storage duration** is either ordered or
- unordered. Definitions of explicitly specialized class template static data members have ordered initialization.
- Other class template static data members (i.e., implicitly or explicitly instantiated specializations) have
- unordered initialization. **Other non-local variables with static storage duration have ordered initialization.
- Variables with ordered initialization defined within a single translation unit shall be initialized in the order
- of their definitions in the translation unit.**
- Regarding thread storage, the same section continues, emphasis mine:
- > If a program starts a thread (30.3), the subsequent initialization
- of a variable is unsequenced with respect to the initialization of a variable defined in a different translation
- unit. Otherwise, the initialization of a variable is indeterminately sequenced with respect to the initialization
- of a variable defined in a different translation unit. **If a program starts a thread, the subsequent unordered
- initialization of a variable is unsequenced with respect to every other dynamic initialization. Otherwise,
- the unordered initialization of a variable is indeterminately sequenced with respect to every other dynamic
- initialization.**
- TL;DR
- The initialization of the variables `a` and `b` in your question are indeterminately sequenced in relation to each other. The initialization order is not guaranteed between them.
- ---
- The initialization rules of C++ are quite complex, especially past C++11. The relevant part would be C++11 3.6.2, "Initialization of non-local variables" which speaks of zero initialization, then constant initialization. The formal terms are defined as
- > Together, zero-initialization and constant initialization are called _static initialization_; all other initialization
- is _dynamic initialization_.
- Your specific case sorts under dynamic initialization, even if the storage duration of the objects are static/thread storage. Static storage variables have the following rules, emphasis mine:
- > **Dynamic initialization of a non-local variable with static storage duration** is either ordered or
- unordered. Definitions of explicitly specialized class template static data members have ordered initialization.
- Other class template static data members (i.e., implicitly or explicitly instantiated specializations) have
- unordered initialization. **Other non-local variables with static storage duration have ordered initialization.
- Variables with ordered initialization defined within a single translation unit shall be initialized in the order
- of their definitions in the translation unit.**
- Regarding thread storage, the same section continues, emphasis mine:
- > If a program starts a thread (30.3), the subsequent initialization
- of a variable is unsequenced with respect to the initialization of a variable defined in a different translation
- unit. Otherwise, the initialization of a variable is indeterminately sequenced with respect to the initialization
- of a variable defined in a different translation unit. **If a program starts a thread, the subsequent unordered
- initialization of a variable is unsequenced with respect to every other dynamic initialization. Otherwise,
- the unordered initialization of a variable is indeterminately sequenced with respect to every other dynamic
- initialization.**
#1: Initial revision
by
Lundin
·
2020-11-17T15:55:53Z (almost 4 years ago)
TL;DR The variables `a` and `b` in your question are indeterminately sequenced in relation to each other. The initialization order is not guaranteed between them. --- The initialization rules of C++ are quite complex, especially past C++11. The relevant part would be C++11 3.6.2, "Initialization of non-local variables" which speaks of zero initialization, then constant initialization. The formal terms are defined as > Together, zero-initialization and constant initialization are called _static initialization_; all other initialization is _dynamic initialization_. Your specific case sorts under dynamic initialization, even if the storage duration of the objects are static/thread storage. Static storage variables have the following rules, emphasis mine: > **Dynamic initialization of a non-local variable with static storage duration** is either ordered or unordered. Definitions of explicitly specialized class template static data members have ordered initialization. Other class template static data members (i.e., implicitly or explicitly instantiated specializations) have unordered initialization. **Other non-local variables with static storage duration have ordered initialization. Variables with ordered initialization defined within a single translation unit shall be initialized in the order of their definitions in the translation unit.** Regarding thread storage, the same section continues, emphasis mine: > If a program starts a thread (30.3), the subsequent initialization of a variable is unsequenced with respect to the initialization of a variable defined in a different translation unit. Otherwise, the initialization of a variable is indeterminately sequenced with respect to the initialization of a variable defined in a different translation unit. **If a program starts a thread, the subsequent unordered initialization of a variable is unsequenced with respect to every other dynamic initialization. Otherwise, the unordered initialization of a variable is indeterminately sequenced with respect to every other dynamic initialization.**