std::is_error_code_enum

From cppreference.com

Compiler support
Freestanding and hosted
Language
Standard library
Standard library headers
Named requirements
Feature test macros(C++20)
Language support library
Concepts library(C++20)
Diagnostics library
Memory management library
Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
Algorithms library
Strings library
Text processing library
Numerics library
Date and time library
Input/output library
Filesystem library(C++17)
Concurrency support library(C++11)
Execution control library(C++26)
Technical specifications
Symbols index
External libraries

[edit]

Utilities library

Language support

Type support (basic types, RTTI)

Library feature-test macros(C++20)

Program utilities

Variadic functions

initializer_list

(C++11)

is_constant_evaluated

(C++20)

is_within_lifetime

(C++26)

source_location

(C++20)

Coroutine support(C++20)

Contract support(C++26)

Three-way comparison

three_way_comparablethree_way_comparable_with

(C++20)(C++20)

strong_ordering

(C++20)

weak_ordering

(C++20)

partial_ordering

(C++20)

common_comparison_category

(C++20)

compare_three_way_result

(C++20)

(C++20)

(C++20)

(C++20)

(C++20)

compare_strong_order_fallback

(C++20)

compare_weak_order_fallback

(C++20)

compare_partial_order_fallback

(C++20)

is_eqis_ltis_lteq

(C++20)(C++20)(C++20)

is_neqis_gtis_gteq

(C++20)(C++20)(C++20)

General utilities

Function objects
Bit manipulation(C++20)
C-style bit manipulation(C++26)
bitset
hash (C++11)

Relational operators(deprecated in C++20)

rel_ops::operator!=rel_ops::operator>

rel_ops::operator<=rel_ops::operator>=

Integer comparison functions

cmp_equalcmp_lesscmp_less_than

(C++20)(C++20)(C++20)

cmp_not_equalcmp_greatercmp_greater_than

(C++20)(C++20)(C++20)

in_range

(C++20)

Swap andtype operations

swap
ranges::swap (C++20)
exchange (C++14)
declval (C++11)
to_underlying (C++23)

forward (C++11)
forward_like (C++23)
move (C++11)
move_if_noexcept (C++11)
as_const (C++17)

Common vocabulary types

pair
tuple (C++11)
optional (C++17)
any (C++17)
variant (C++17)

tuple_size (C++11)
tuple_element (C++11)
apply (C++17)
make_from_tuple (C++17)
expected (C++23)

[edit]

Diagnostics library

Exception handling
exception
uncaught_exceptionuncaught_exceptions (until C++20*) (C++17)
exception_ptr (C++11)
make_exception_ptr (C++11)
current_exception (C++11)
rethrow_exception (C++11)
nested_exception (C++11)
throw_with_nested (C++11)
rethrow_if_nested (C++11)
Exception handling failures
terminate
terminate_handler
get_terminate (C++11)
set_terminate
bad_exception
unexpected (until C++17*)
unexpected_handler (until C++17*)
get_unexpected (until C++17*)
set_unexpected (until C++17*)
Error numbers
Error codes
errno
Assertions
assert

Exception categories
logic_error
invalid_argument
domain_error
length_error
out_of_range
runtime_error
range_error
overflow_error
underflow_error
tx_exception (TM TS)
System error
error_category (C++11)
generic_category (C++11)
system_category (C++11)
error_condition (C++11)
errc (C++11)
error_code (C++11)
system_error (C++11)
Stacktrace
stacktrace_entry (C++23)
basic_stacktrace (C++23)
Debugging support
is_debugger_present (C++26)
breakpoint_if_debugging (C++26)
breakpoint (C++26)

[edit]

std::error_code

Member functions
error_code::error_code
error_code::operator=
error_code::assign
Modifiers
error_code::clear
Observers
error_code::value
error_code::category
error_code::default_error_condition
error_code::message
error_code::operator bool
Non-member functions
operator==operator!=operator<operator<=> (until C++20)(until C++20)(C++20)
operator<<
Helper classes
is_error_code_enum
hash<std::error_code>

[edit]

Defined in header`<system_error>`
template<class T> struct is_error_code_enum;		(since C++11)

IfT is an error code enumeration (such asstd::io_errc andstd::future_errc), this template provides the member constantvalue equaltrue. For any other type,value isfalse.

This template may be specialized for aprogram-defined type to indicate that the type is eligible forstd::error_code implicit conversion.

[edit]Helper variable template

template<class T> constexprbool is_error_code_enum_v= is_error_code_enum<T>::value;		(since C++17)

[edit]

Inherited fromstd::integral_constant

Member constants

value

[static]

true ifT is an error code enum,false otherwise
(public static member constant)

Member functions

operator bool	converts the object tobool, returnsvalue (public member function)
operator() (C++14)	returnsvalue (public member function)

Member types

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

Run this code

#include <ios>#include <system_error> static_assert(std::is_error_code_enum_v<decltype(std::io_errc::stream)>);static_assert(!std::is_error_code_enum_v<std::error_category>); int main(){}