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POnon-deferred static member initialization for templates in gcc?
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  1. POnon-deferred static member initialization for templates in gcc?
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    copied!<p>Does gcc have any guarantees about static member initialization timing, especially regarding template classes?</p> <p>I want to know if I can get a hard guarantee that static members (<code>PWrap_T&lt;T&gt;::p_s</code>) will be initialized before <code>main()</code>, when classes are instantiated across multiple compilation units. It isn't practical to try to manually touch a symbol from each compilation unit at the start of main, but it isn't clear to me that anything else would work.</p> <p>I've tested with methods like <code>bar()</code> in different units and <em>always</em> gotten the desired result, but I need to know when/if ever gcc will yank the rug out and whether it's preventable.</p> <p>Furthermore, will all static members from a DSO be initialized before a library finishes loading?</p> <pre><code>#include &lt;iostream&gt; #include &lt;deque&gt; struct P; inline std::deque&lt;P *&gt; &amp;ps() { static std::deque&lt;P *&gt; d; return d; } void dump(); struct P { P(int id, char const *i) : id_(id), inf_(i) { ps().push_back(this); } void doStuff() { std::cout &lt;&lt; id_ &lt;&lt; " (" &lt;&lt; inf_ &lt;&lt; ")" &lt;&lt; std::endl; } int const id_; char const *const inf_; }; template &lt;class T&gt; struct PWrap_T { static P p_s; }; // *** Can I guarantee this is done before main()? *** template &lt;class T&gt; P PWrap_T&lt;T&gt;::p_s(T::id(), T::desc()); #define PP(ID, DESC, NAME) /* semicolon must follow! */ \ struct ppdef_##NAME { \ constexpr static int id() { return ID; } \ constexpr static char const *desc() { return DESC; } \ }; \ PWrap_T&lt;ppdef_##NAME&gt; const NAME // In a compilation unit apart from the template/macro header. void dump() { std::cout &lt;&lt; "["; for (P *pp : ps()) { std::cout &lt;&lt; " " &lt;&lt; pp-&gt;id_ &lt;&lt; ":" &lt;&lt; pp-&gt;inf_; } std::cout &lt;&lt; " ]" &lt;&lt; std::endl; } // In some compilation unit. void bar(int cnt) { for (int i = 0; i &lt; cnt; ++i) { PP(2, "description", pp); pp.p_s.doStuff(); } } int main() { dump(); PP(3, "another", pp2); bar(5); pp2.p_s.doStuff(); } </code></pre> <blockquote> <p><strong>(C++11 §3.6.2/4 - [basic.start.init]:)</strong></p> <p>It is implementation-defined whether the dynamic initialization of a non-local variable with static storage duration is done before the first statement of main. <strong>If the initialization is deferred to some point in time after the first statement of main, it shall occur before the first odr-use (3.2) of any function or variable defined in the same translation unit as the variable to be initialized.</strong></p> <p>... A non-local variable with static storage duration having initialization with side-effects must be initialized even if it is not odr-used (3.2, 3.7.1).</p> </blockquote> <p>Also, trying <code>__attribute__ ((init_priority(int)))</code> or <code>__attribute__ ((constructor))</code> for the template member's initialization yielded <code>warning: attributes after parenthesized initializer ignored</code>, and I know no other tricks regarding static initialization.</p> <p>Thanks in advance to anyone who can give me an answer about this!</p>
 

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