std::function<R(Args...)>::operator()
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.
Parameters
| args | - | parameters to pass to the stored callable function target |
Return value
None if R is void. Otherwise the return value of the invocation of the stored callable object.
Exceptions
Throws std::bad_function_call if *this does not store a callable function target, i.e. !*this == true.
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.
#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
See also
| invokes the target (public member function of std::move_only_function) |
|
| calls the stored function (public member function of std::reference_wrapper<T>) |
|
|
(C++11) | the exception thrown when invoking an empty std::function (class) |
|
(C++17)(C++23) | invokes any Callable object with given arguments and possibility to specify return type(since C++23) (function template) |
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