std::function<R(Args...)>::operator()
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std::function
R operator()( Args... args ) const;
(since C++11)
Invokes the stored callable function target with the parameters args.
Effectively does INVOKE<R> (f, std::forward <Args>(args)...), where f is the target object of *this.
[edit] Parameters
args
-
parameters to pass to the stored callable function target
[edit] Return value
None if R is void. Otherwise the return value of the invocation of the stored callable object.
[edit] Exceptions
Throws std::bad_function_call if *this does not store a callable function target, i.e. !*this == true.
[edit] Example
The following example shows how std::function can be passed to other functions by value. Also, it shows how std::function can store lambdas.
Run this code
#include <functional> #include <iostream> void call(std::function <int()> f) // can be passed by value { std::cout << f() << '\n'; } int normal_function() { return 42; } int main() { int n = 1; std::function <int()> f; try { call(f); } catch (const std::bad_function_call & ex) { std::cout << ex.what() << '\n'; } f = [&n](){ return n; }; call(f); n = 2; call(f); f = normal_function; call(f); std::function <void(std::string, int)> g; g = [](std::string str, int i) { std::cout << str << ' ' << i << '\n'; }; g("Hi", 052); }
Possible output:
bad_function_call 1 2 42 Hi 42