std-function

问题 This question already has an answer here : Why can't std::function bind to C-style variadic functions? (1 answer) Closed 6 years ago . I have a structure that I pass around my application which contains a bunch of callback functions: typedef struct { std::function<void (void)> f1; std::function<void (int)> f2; std::function<int (float *)> f3; // ... and so on } CallbackTable; I handle state control within the application by binding different functions to the various callbacks, depending upon

问题 In below code snippet while calling call back function "Invalid use of void expression" error is flashed by the compiler. #include <iostream> #include <functional> using namespace std; template<class type> class State { public: State(type type1,const std::function<void (type type1 )> Callback) { } }; template <class type> void Callback(type type1 ) { //Based on type validation will be done here } int main() { State<int> obj(10,Callback(10)); return 0; } Just want to know what is the wrong

问题 For the struct: struct A { int var = 10; void check() { std::cout << "var is " << var << std::endl; } }; Say I create a std::function object of A::check() , using a dynamically allocated a object: auto a_ptr = std::make_unique<A>(); std::function<void()> f = std::bind(&A::check, a_ptr.get()); //...later/elsewhere... f(); It would be nice for safety if I could test f to see if the bound A object is still alive. Is it possible to retrieve that information from f directly? Assume a_ptr is not

问题 If I need to generate a lambda that calls a member function, should I capture by reference or capture 'this'? My understanding is that '&' captures only the variables used, but 'this' captures all member variable. So better to use '&'? class MyClass { public: int mFunc() { // accesses member variables } std::function<int()> get() { //return [this] () { return this->mFunc(); }; // or //return [&] () { return this->mFunc(); }; } private: // member variables } 回答1: For the specific example you

问题 I have an std::function object I'm using as a callback to some event. I'm assigning a lambda to this object, within which, I assign the object to a different lambda mid execution. I get a segfault when I do this. Is this not something I'm allowed to do? If so, why? And how would I go about achieving this? declaration: std::function<void(Data *)> doCallback; calling: // // This gets called after a sendDataRequest call returns with data // void onIncomingData(Data *data) { if ( doCallback ) {

问题 While std::function is movable, in some cases it's not possible or not convenient. Is there a significant penalty for copying it? Does it possibly depend on the size of the captured variables (if it was created using a lambda expression)? Is it implementation dependent? 回答1: It is indeed implementation-dependent. It also depends on what exactly you are storing in the std::function . It is surely not as cheap as simply copying a C-style function pointer. The best thing would be for you to try

问题 I have defined class template named CallBackAtInit which only purpose is to call a function at its initialization (constructor). The function is specified in template parameters. The problem is that templates does not accept std::function as parameters; but they accept function pointers. Why? Here is my code: #include <iostream> #include <functional> /* Does not work:*/ template <typename return_type, typename arg_type, std::function<return_type(arg_type)> call_back> /* Work fine: *///

问题 The following program do not compile : #include <iostream> #include <vector> #include <functional> #include <algorithm> #include <cstdlib> #include <cmath> void asort(std::vector<double>& v, std::function<bool(double, double)> f) { std::sort(v.begin(), v.end(), [](double a, double b){return f(std::abs(a), std::abs(b));}); } int main() { std::vector<double> v({1.2, -1.3, 4.5, 2.3, -10.2, -3.4}); for (unsigned int i = 0; i < v.size(); ++i) { std::cout<<v[i]<<" "; } std::cout<<std::endl; asort(v

问题 Is it possible to call function objects created with std::bind using std::async. The following code fails to compile: #include <iostream> #include <future> #include <functional> using namespace std; class Adder { public: int add(int x, int y) { return x + y; } }; int main(int argc, const char * argv[]) { Adder a; function<int(int, int)> sumFunc = bind(&Adder::add, &a, 1, 2); auto future = async(launch::async, sumFunc); // ERROR HERE cout << future.get(); return 0; } The error is: No matching

问题 Is it possible to call function objects created with std::bind using std::async. The following code fails to compile: #include <iostream> #include <future> #include <functional> using namespace std; class Adder { public: int add(int x, int y) { return x + y; } }; int main(int argc, const char * argv[]) { Adder a; function<int(int, int)> sumFunc = bind(&Adder::add, &a, 1, 2); auto future = async(launch::async, sumFunc); // ERROR HERE cout << future.get(); return 0; } The error is: No matching