c++ - How to use lambda functions or std::function with an API that takes function pointers? -

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suppose want implement simple abstraction on pthreads. (or c api takes function pointers callbacks or threads).

like std::thread, want interface able take function objects in general.

how bridge gap in way works cases? (that includes binds, lambda functions, etc.)

i know std::function::target afaik, not need.

if api takes functions void* user data as, e.g., pthread_create() does, you'd pass pointer function user data, call trampoline casts user data function type, , calls function. example:

#include <functional> #include <pthread.h>  extern "c" void* trampoline(void* userdata) {     return (*static_cast<std::function<void*()>*>(userdata))(); }  void* start() {     // ...     return 0; }  int main() {     pthread_t thread;     std::function<void*()> entry(start);     pthread_create(&thread, 0, &trampoline, &entry);     // ... }

the immediate implication is, however, function object life-time isn't controlled. in example above std::function<void*()> object happens live long enough isn't easy.

if function try call doesn't have user data argument, pretty out of luck. might away using global objects rather fragile approach.


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