Namespaces
Variants
Actions

operator==,!=(std::function)

From cppreference.com
< cpp‎ | utility‎ | functional‎ | function
 
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
(C++20)(C++20)(C++20)  
(C++20)
(C++20)
(C++14)
(C++11)
(C++11)
(C++23)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++17)
(C++23)


 
Function objects
(C++17)(C++23)
Identity function object
(C++20)
(until C++17*)
(until C++17*)
(until C++17*)
(until C++17*)  
(until C++17*)
(until C++17*)(until C++17*)(until C++17*)(until C++17*)
(until C++20*)
(until C++20*)
(until C++17*)(until C++17*)
(until C++17*)(until C++17*)

(until C++17*)
(until C++17*)(until C++17*)(until C++17*)(until C++17*)
(until C++20*)
(until C++20*)
 
 
Defined in header <functional>
template< class R, class... ArgTypes >

bool operator==( const std::function <R(ArgTypes...)>& f,

                 std::nullptr_t ) noexcept;
(1) (since C++11)
template< class R, class... ArgTypes >

bool operator==( std::nullptr_t,

                 const std::function <R(ArgTypes...)>& f ) noexcept;
(2) (since C++11)
(until C++20)
template< class R, class... ArgTypes >

bool operator!=( const std::function <R(ArgTypes...)>& f,

                 std::nullptr_t ) noexcept;
(3) (since C++11)
(until C++20)
template< class R, class... ArgTypes >

bool operator!=( std::nullptr_t,

                 const std::function <R(ArgTypes...)>& f ) noexcept;
(4) (since C++11)
(until C++20)

Compares a std::function with a null pointer. Empty functions (that is, functions without a callable target) compare equal, non-empty functions compare non-equal.

The != operator is synthesized from operator==.

(since C++20)

[edit] Parameters

f - std::function to compare

[edit] Return value

1,2) !f
3,4) (bool) f

[edit] Example

Run this code
#include <functional>
#include <iostream>
 
using SomeVoidFunc = std::function <void(int)>;
 
class C
{
public:
 C(SomeVoidFunc void_func = nullptr) : void_func_(void_func)
 {
 if (void_func_ == nullptr) // specialized compare with nullptr
 void_func_ = std::bind (&C::default_func, this, std::placeholders::_1);
 void_func_(7);
 }
 
 void default_func(int i) { std::cout << i << '\n'; };
 
private:
 SomeVoidFunc void_func_;
};
 
void user_func(int i)
{
 std::cout << (i + 1) << '\n';
}
 
int main()
{
 C c1;
 C c2(user_func);
}

Output:

7
8

[edit] See also

(C++23)
compares a std::move_only_function with nullptr
(function) [edit]
Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/utility/functional/function/operator_cmp&oldid=161378"

AltStyle によって変換されたページ (->オリジナル) /