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C++ Functional Library - operator==,!=(std::function)
Description
It 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.
Declaration
Following is the declaration for std::function.
template< class R, class... ArgTypes > bool operator==( const std::function<R(ArgTypes...)>& f, std::nullptr_t )
C++11
template< class R, class... ArgTypes > bool operator==( const std::function<R(ArgTypes...)>& f, std::nullptr_t )
Parameters
f − It is used to compare between functions.
Return Value
none
Exceptions
noexcep − It doesn't throw any exceptions.
Example
In below example explains about std::function.
#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) { void_func_ = std::bind(&C::default_func, this, std::placeholders::_1); } void_func_(9); } 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); }
Let us compile and run the above program, this will produce the following result −
9 10
functional.htm
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