8 Statements [stmt.stmt]

8.8 Declaration statement [stmt.dcl]

1
#
A declaration statement introduces one or more new names into a block; it has the form
[Note 1: 
If an identifier introduced by a declaration was previously declared in an outer block, the outer declaration is hidden for the remainder of the block ([basic.lookup.unqual]), after which it resumes its force.
— end note]
2
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A block variable with automatic storage duration ([basic.stc.auto]) is active everywhere in the scope to which it belongs after its init-declarator.
Upon each transfer of control (including sequential execution of statements) within a function from point P to point Q, all block variables with automatic storage duration that are active at P and not at Q are destroyed in the reverse order of their construction.
Then, all block variables with automatic storage duration that are active at Q but not at P are initialized in declaration order; unless all such variables have vacuous initialization ([basic.life]), the transfer of control shall not be a jump.74
When a declaration-statement is executed, P and Q are the points immediately before and after it; when a function returns, Q is after its body.
[Example 1: void f() { // ... goto lx; // error: jump into scope of a // ... ly: X a = 1; // ... lx: goto ly; // OK, jump implies destructor call for a followed by // construction again immediately following label ly } — end example]
3
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Dynamic initialization of a block variable with static storage duration or thread storage duration is performed the first time control passes through its declaration; such a variable is considered initialized upon the completion of its initialization.
If the initialization exits by throwing an exception, the initialization is not complete, so it will be tried again the next time control enters the declaration.
If control enters the declaration concurrently while the variable is being initialized, the concurrent execution shall wait for completion of the initialization.
[Note 2: 
A conforming implementation cannot introduce any deadlock around execution of the initializer.
Deadlocks might still be caused by the program logic; the implementation need only avoid deadlocks due to its own synchronization operations.
— end note]
If control re-enters the declaration recursively while the variable is being initialized, the behavior is undefined.
[Example 2: int foo(int i) { static int s = foo(2*i); // undefined behavior: recursive call return i+1; } — end example]
4
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An object associated with a block variable with static or thread storage duration will be destroyed if and only if it was constructed.
[Note 3: 
[basic.start.term] describes the order in which such objects are destroyed.
— end note]
74)74)
The transfer from the condition of a switch statement to a case label is considered a jump in this respect.