std::is_convertible

Defined in header `<type_traits>`
template< class From, class To > struct is_convertible;		(since C++11)

If the return statement in the imaginary function definition To test() { return std::declval<From>(); } is well-formed, (that is, if std::declval<From>() can be converted to To using implicit conversion), provides the member constant value equal to true. Otherwise value is false. For the purposes of this check, the use of std::declval is in the return statement is not considered an odr-use.

Access checks are performed as if from a context unrelated to either type. Only the validity of the immediate context of the expression in the return statement (including conversions to the return type) is considered.

From and To shall each be a complete type, (possibly cv-qualified) void, or an array of unknown bound. Otherwise, the behavior is undefined.

Inherited from std::integral_constant

Member constants

value

[static]

true if From is convertible to To , false otherwise
(public static member constant)

Member functions

operator bool	converts the object to bool, returns `value` (public member function)
operator() (C++14)	returns `value` (public member function)

Member types

Type	Definition
`value_type`	`bool`
`type`	std::integral_constant<bool, value>

[edit] Notes

Gives well-defined results for reference types, void types, array types, and function types.

[edit] Example

Run this code

#include <iostream>
#include <type_traits>
 
int main() 
{
    class A {};
    class B : public A {};
    class C {};
 
    bool b2a = std::is_convertible<B*, A*>::value;
    bool a2b = std::is_convertible<A*, B*>::value;
    bool b2c = std::is_convertible<B*, C*>::value;
 
    std::cout << std::boolalpha;
    std::cout << b2a << '\n';
    std::cout << a2b << '\n';
    std::cout << b2c << '\n';
}

Output:

true
false
false

[edit] See also

std::experimental::is_convertible_v

(library fundamentals TS)

variable template alias of std::is_convertible::value
(variable template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Date and time
Function objects
initializer_list (C++11)
bitset
hash (C++11)
Relational operators
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Optional and any
optional (C++17)
any (C++17)
Pairs and tuples
pair
tuple (C++11)
apply (C++17)
piecewise_construct_t (C++11)
piecewise_construct (C++11)
integer_sequence (C++14)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Type operations
declval (C++11)
as_const (C++17)