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std::function<R(Args...)>::operator()

From cppreference.com
< cpp‎ | utility‎ | functional‎ | function
 
 
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(until C++17*)
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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.

Contents

[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.

#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 = [&n](){ return n; };
    call(f);
 
    n = 2;
    call(f);
 
    f = normal_function;
    call(f);
}

Output:

1
2
42

[edit] See also

invokes the target
(public member function of std::move_only_function) [edit]
calls the stored function
(public member function of std::reference_wrapper<T>) [edit]
the exception thrown when invoking an empty std::function
(class) [edit]
(C++17)(C++23)
invokes any Callable object with given arguments and possibility to specify return type(since C++23)
(function template) [edit]