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std:: bad_function_call

From cppreference.net
C++
Utilities library
Function objects
Function wrappers
(C++11)
(C++23)
(C++26)
(C++26)
(C++11)
bad_function_call
(C++11)
Function invocation
(C++17) (C++23)
Identity function object
(C++20)
Old binders and adaptors
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Defined in header <functional>
class bad_function_call ;

std::bad_function_call is the type of the exception thrown by std::function::operator() if the function wrapper has no target.

cpp/error/exception std-bad function call-inheritance.svg

Inheritance diagram

Contents

Member functions

(constructor)
constructs a new bad_function_call object
(public member function)
operator=
replaces the bad_function_call object
(public member function)
what
returns the explanatory string
(public member function)

std::bad_function_call:: bad_function_call

bad_function_call ( ) noexcept ;
(1) (since C++11)
bad_function_call ( const bad_function_call & other ) noexcept ;
(2) (since C++11)

Constructs a new bad_function_call object with an implementation-defined null-terminated byte string which is accessible through what() .

1) Default constructor.
2) Copy constructor. If * this and other both have dynamic type std::bad_function_call then std:: strcmp ( what ( ) , other. what ( ) ) == 0 .

Parameters

other - another exception object to copy

std::bad_function_call:: operator=

bad_function_call & operator = ( const bad_function_call & other ) noexcept ;
(since C++11)

Assigns the contents with those of other . If * this and other both have dynamic type std::bad_function_call then std:: strcmp ( what ( ) , other. what ( ) ) == 0 after assignment.

Parameters

other - another exception object to assign with

Return value

* this

std::bad_function_call:: what

virtual const char * what ( ) const noexcept ;
(since C++11)

Returns the explanatory string.

Return value

Pointer to an implementation-defined null-terminated string with explanatory information. The string is suitable for conversion and display as a std::wstring . The pointer is guaranteed to be valid at least until the exception object from which it is obtained is destroyed, or until a non-const member function (e.g. copy assignment operator) on the exception object is called.

Notes

Implementations are allowed but not required to override what() .

Inherited from std:: exception

Member functions

[virtual]
destroys the exception object
(virtual public member function of std::exception )
[virtual]
returns an explanatory string
(virtual public member function of std::exception )

Example

Run this code 
#include <functional>
#include <iostream>
int main()
{
    std::function<int()> f = nullptr;
    try
    {
        f();
    }
    catch (const std::bad_function_call& e)
    {
        std::cout << e.what() << '\n';
    }
}

Possible output: 

bad function call

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2233 C++11 what() always returned the same explanatory
string as std::exception::what() 		returns its own
explanatory string

See also

(C++11)
copyable wrapper of any copy constructible callable object
(class template)