operator==,!=(std::function)
From cppreference.com
< cpp | utility | functional | function
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
Utilities library
Type support (basic types, RTTI)
Library feature-test macros (C++20)
(C++11)
(C++20)
(C++26)
(C++20)
Coroutine support (C++20)
Contract support (C++26)
(C++20)(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)(C++20)(C++20)
(C++20)(C++20)(C++20)
General utilities
Relational operators (deprecated in C++20)
(C++20)(C++20)(C++20)
(C++20)(C++20)(C++20)
(C++20)
Swap and type operations
Common vocabulary types
Function objects
(C++11)
(C++23)
(C++26)
(C++26)
(C++11)
(C++11)
(C++20)(C++23)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)
(C++11)(C++11)
(C++20)(C++20)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++17)
(C++17)
(C++17)
(C++17)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
(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++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*)
std::function
Defined in header
<functional>
template< class R, class... ArgTypes >
(1)
(since C++11)
bool operator==( const std::function <R(ArgTypes...)>& f,
template< class R, class... ArgTypes >
(2)
(since C++11) bool operator==( std::nullptr_t,
(until C++20)
template< class R, class... ArgTypes >
(3)
(since C++11) bool operator!=( const std::function <R(ArgTypes...)>& f,
(until C++20)
template< class R, class... ArgTypes >
(4)
(since C++11) bool operator!=( std::nullptr_t,
(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==.
Contents
[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