std::mem_fun_t, std::mem_fun1_t, std::const_mem_fun_t, std::const_mem_fun1_t

std::mem_fun_t, std::mem_fun1_t, std::const_mem_fun_t, std::const_mem_fun1_t - cppreference.com

From cppreference.com

Defined in header `<functional>`
`template< class S, class T > class mem_fun_t : public unary_function<T,S> { public: explicit mem_fun_t(S (T::p)()); S operator()(T* p) const; };`	(1)	(deprecated in C++11) (removed in C++17)
`template< class S, class T > class const_mem_fun_t : public unary_function<const T,S> { public: explicit const_mem_fun_t(S (T::p)() const); S operator()(const T* p) const; };`	(2)	(deprecated in C++11) (removed in C++17)
`template< class S, class T, class A > class mem_fun1_t : public binary_function<T,A,S> { public: explicit mem_fun1_t(S (T::p)(A)); S operator()(T* p, A x) const; };`	(3)	(deprecated in C++11) (removed in C++17)
`template< class S, class T, class A > class const_mem_fun1_t : public binary_function<const T,A,S> { public: explicit const_mem_fun1_t(S (T::p)(A) const); S operator()(const T* p, A x) const; };`	(4)	(deprecated in C++11) (removed in C++17)

Wrapper around a member function pointer. The class instance whose member function to call is passed as a pointer to the operator().

1) Wraps a non-const member function with no parameters.

2) Wraps a const member function with no parameters.

3) Wraps a non-const member function with a single parameter.

4) Wraps a const member function with a single parameter.