If a function is reentered during the initialization of a static object inside that function, the behavior of the program is undefined. Please note that this is a different problem is not the same as infinite recursion. For this problem to occur, a function only needs to recurse once.
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The zero-initialization of all local objects with static storage duration or thread storage duration is performed before any other initialization takes place. Constant initialization of a local entity with static storage duration, if applicable, is performed before its block is ?rst first entered. An implementation is permitted to perform early initialization of other local objects with static or thread storage duration under the same conditions that an implementation is permitted to statically initialize an object with static or thread storage duration in namespace scope. Otherwise such an object is initialized the ?rst first time control passes through its declaration; such an object 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 object is being initialized, the concurrent execution shall wait for completion of the initialization. If control re-enters the declaration recursively while the object is being initialized, the behavior is unde?nedundefined.
Noncompliant Code Example
This noncompliant code example declares the variable y as a static int. The value of test( x) is assigned to y within the test(int x) function. However, when test(int x) is called with an input which that results in reaching the initialization of y more than once, such as the value 12, undefined behavior occurs. Note that this code does not present an infinite recursion and still causes the undefined behavior mentioned.
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Implementation-Specific Details
In gcc3the GCC3 compiler, this code will recurse as if y were a non-static variable.
In gcc4the GCC4 compiler, upon reaching the initialization of y for the second time, the program will terminate with the following message:
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In this compliant solution, {{y}} is declared before being assigned a value. According to \[[ISO/IEC 14882-2003|AA. C++ References#ISO/IEC 14882-2003]\] Section 6.7.4, the initialization of {{y}} will have been completed at the end of the declaration and before the assignment of a value, thusconsequently removing the possibility of undefined behavior. |
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