c++ - How to use bind correctly here? -

i can not figure out correct syntax bind member functions. if have function takes function single argument, how pass object it?

in following example, correct syntax of passing function?

#include <iostream> #include <functional> void caller(std::function<void(int)> f) {     f(42); } class foo { public:     void f(int x)     {         std::cout<<x<<std::endl;     } }; int main() {     foo obj;     caller(std::bind(&foo::f,obj));     //^wrong }  

error was:

a.cpp: in function ‘int main()’: a.cpp:18:34: error: not convert ‘std::bind(_func&&, _boundargs&& ...) [with _func = void (foo::*)(int); _boundargs = {foo&}; typename std::_bind_helper<std::__or_<std::is_integral<typename std::decay<_tp>::type>, std::is_enum<typename std::decay<_tp>::type> >::value, _func, _boundargs ...>::type = std::_bind<std::_mem_fn<void (foo::*)(int)>(foo)>]((* & obj))’ ‘std::_bind_helper<false, void (foo::*)(int), foo&>::type {aka std::_bind<std::_mem_fn<void (foo::*)(int)>(foo)>}’ ‘std::function<void(int)>’      caller(std::bind(&foo::f,obj)); 

placeholders create "space" actual arguments bound later:

int main() {     foo obj;     caller(std::bind(&foo::f, &obj, std::placeholders::_1));     //                                   ^ placeholder     //                        ^ address or foo() } 

these placeholders needed correctly generate appropriate signature std::bind result bound std::function<void(int)>.

you may want use address of object, or std::ref (so won't copied); vary on want semantics be.