StackOverflow2013

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copied!<p>There is no such thing as an anonymous function in C (C++ is irrelevant here, as the function must abide by the C calling convention).</p> <p>The only thing you can do is <em>shiver</em> access globals from the handler, probably global <em>variables</em> (and not constants which would be fine).</p> <p>I advise making those globals <em>thread local</em> to avoid multithreading issues, but it is still <em>bad</em> in the sense that global variables make for more brittle applications.</p> <hr> <p><strong>How to ?</strong></p> <p><em>Note: as Luc Danton patiently explained to me, a signal may interrupt any non-atomic activity, and thus reading from a global is safe only if it is a lock-free atomic (or a few other things). <strong>Unfortunately <code>std::function</code> may not be so, depending on your implementation</strong>, I will still leave this code to explain how it could be done <strong>providing that <code>std::function</code> accesses are atomic</strong>.</em></p> <p>It is possible to create a trampoline that will call stateful stuff, isolating thread and allowing re-entrant calls.</p> <pre><code>typedef std::function<void(int)> SignalHandlerType; extern thread_local ignalHandlerType SignalHandler; </code></pre> <p>And we create the following accessor (passed to signal):</p> <pre><code>void handle_signal(int const i) { if (SignalHandler) { SignalHandler(i); } } </code></pre> <p>as well as the following RAII setter:</p> <pre><code>class SignalSetter: boost::noncopyable { public: SignalSetter(int signal, SignalHandlerType&& sh): signal(signal), chandler(0), handler(sh) { chandler = std::signal(signal, &handle_signal<T>); swap(SignalHandler, handler); } ~SignalSetter() { std::signal(signal, chandler); swap(SignalHandler, handler); } private: typedef void(*CHandlerType)(int); int signal; CHandlerType chandler; SignalHandlerType handler; }; </code></pre> <p><em>Note: both the global variable and the <code>handle_signal</code> could be <code>private</code> to the <code>SignalSetter</code> class... but since <code>std::signal</code> is not...</em></p> <p>Expected usage:</p> <pre><code>int main(int argc, char* argv[]) { SignalSetter setter(SIGFPE, [argc, argv]() { std::cout << argc << ": " << argc << std::endl; }); // do what you want. } </code></pre>

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