operator==,!=(std::function)
< cpp | utility | functional | function
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) |
template< class R, class... ArgTypes > bool operator!=( const std::function<R(ArgTypes...)>& f, std::nullptr_t ) noexcept; |
(3) | (since C++11) |
template< class R, class... ArgTypes > bool operator!=( std::nullptr_t, const std::function<R(ArgTypes...)>& f ) noexcept; |
(4) | (since C++11) |
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.
Parameters
f | - | std::function to compare
|
Return value
1-2) !f
3-4) (bool) f
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