<functional> operators

The latest version of this topic can be found at <functional> operators.

operator==

Tests if callable object is empty.

template <class Fty>  
bool operator==(const function<Fty>& f, null_ptr_type npc);

template <class Fty>  
bool operator==(null_ptr_type npc, const function<Fty>& f);

Parameters

Fty
The function type to wrap.

f
The function object

npc
A null pointer.

Remarks

The operators both take an argument that is a reference to a function object and an argument that is a null pointer constant. Both return true only if the function object is empty.

Example

// std_tr1__functional__operator_eq.cpp   
// compile with: /EHsc   
#include <functional>   
#include <iostream>   
  
int neg(int val)   
    {   
    return (-val);   
    }   
  
int main()   
    {   
    std::function<int (int)> fn0;   
    std::cout << std::boolalpha << "empty == "   
        << (fn0 == 0) << std::endl;   
  
    std::function<int (int)> fn1(neg);   
    std::cout << std::boolalpha << "empty == "   
        << (fn1 == 0) << std::endl;   
  
    return (0);   
    }  
  

empty == true  
empty == false  

operator!=

Tests if callable object is not empty.

template <class Fty>  
bool operator!=(const function<Fty>& f, null_ptr_type npc);

template <class Fty>  
bool operator!=(null_ptr_type npc, const function<Fty>& f);

Parameters

Fty
The function type to wrap.

f
The function object

npc
A null pointer.

Remarks

The operators both take an argument that is a reference to a function object and an argument that is a null pointer constant. Both return true only if the function object is not empty.

Example

// std_tr1__functional__operator_ne.cpp   
// compile with: /EHsc   
#include <functional>   
#include <iostream>   
  
int neg(int val)   
    {   
    return (-val);   
    }   
  
int main()   
    {   
    std::function<int (int)> fn0;   
    std::cout << std::boolalpha << "not empty == "   
        << (fn0 != 0) << std::endl;   
  
    std::function<int (int)> fn1(neg);   
    std::cout << std::boolalpha << "not empty == "   
        << (fn1 != 0) << std::endl;   
  
    return (0);   
    }  
  

not empty == false  
not empty == true  

See Also

<functional>