system_error
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// <system_error> -*- C++ -*-
// Copyright (C) 2007-2026 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file include/system_error
* This is a Standard C++ Library header.
*/
#ifndef _GLIBCXX_SYSTEM_ERROR
#define _GLIBCXX_SYSTEM_ERROR 1
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#include <bits/requires_hosted.h> // OS-dependent
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
#include <bits/c++config.h>
#include <bits/error_constants.h>
#include <iosfwd>
#include <stdexcept>
#if __cplusplus > 201703L
# include <compare>
#endif
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/** @addtogroup diagnostics
* @{
*/
class error_code;
class error_condition;
class system_error;
/// is_error_code_enum
template<typename _Tp>
struct is_error_code_enum : public false_type { };
/// is_error_condition_enum
template<typename _Tp>
struct is_error_condition_enum : public false_type { };
template<>
struct is_error_condition_enum<errc>
: public true_type { };
#if __cplusplus > 201402L
template <typename _Tp>
inline constexpr bool is_error_code_enum_v =
is_error_code_enum<_Tp>::value;
template <typename _Tp>
inline constexpr bool is_error_condition_enum_v =
is_error_condition_enum<_Tp>::value;
#endif // C++17
/// @}
_GLIBCXX_BEGIN_INLINE_ABI_NAMESPACE(_V2)
/** @addtogroup diagnostics
* @{
*/
/** Abstract base class for types defining a category of error codes.
*
* An error category defines a context that gives meaning to the integer
* stored in an `error_code` or `error_condition` object. For example,
* the standard `errno` constants such a `EINVAL` and `ENOMEM` are
* associated with the "generic" category and other OS-specific error
* numbers are associated with the "system" category, but a user-defined
* category might give different meanings to the same numerical values.
*
* A user-defined category can override the `equivalent` member functions
* to define correspondence between errors in different categories.
* For example, a category for errors from disk I/O could consider some
* of its error numbers equivalent to ENOSPC and ENOENT in the generic
* category.
*
* @headerfile system_error
* @since C++11
*/
class error_category
{
public:
constexpr error_category() noexcept = default;
virtual ~error_category();
error_category(const error_category&) = delete;
error_category& operator=(const error_category&) = delete;
/// A string that identifies the error category.
virtual const char*
name() const noexcept = 0;
// We need two different virtual functions here, one returning a
// COW string and one returning an SSO string. Their positions in the
// vtable must be consistent for dynamic dispatch to work, but which one
// the name "message()" finds depends on which ABI the caller is using.
#if _GLIBCXX_USE_CXX11_ABI
private:
_GLIBCXX_DEFAULT_ABI_TAG
virtual __cow_string
_M_message(int) const;
public:
/// A description of the error condition corresponding to the number.
_GLIBCXX_DEFAULT_ABI_TAG
virtual string
message(int) const = 0;
#else
virtual string
message(int) const = 0;
private:
virtual __sso_string
_M_message(int) const;
#endif
public:
/// Return an error_condition corresponding to `i` in this category.
virtual error_condition
default_error_condition(int __i) const noexcept;
/// Test whether `cond` corresponds to `i` for this category.
virtual bool
equivalent(int __i, const error_condition& __cond) const noexcept;
/// Test whether `code` corresponds to `i` for this category.
virtual bool
equivalent(const error_code& __code, int __i) const noexcept;
/// An error_category only compares equal to itself.
[[__nodiscard__]]
bool
operator==(const error_category& __other) const noexcept
{ return this == &__other; }
/// Ordered comparison that defines a total order for error categories.
#if __cpp_lib_three_way_comparison
[[nodiscard]]
strong_ordering
operator<=>(const error_category& __rhs) const noexcept
{ return std::compare_three_way()(this, &__rhs); }
#else
bool
operator<(const error_category& __other) const noexcept
{ return less<const error_category*>()(this, &__other); }
bool
operator!=(const error_category& __other) const noexcept
{ return this != &__other; }
#endif
};
// DR 890.
/// Error category for `errno` error codes.
[[__nodiscard__, __gnu__::__const__]]
const error_category&
generic_category() noexcept;
/// Error category for other error codes defined by the OS.
[[__nodiscard__, __gnu__::__const__]]
const error_category&
system_category() noexcept;
/// @}
_GLIBCXX_END_INLINE_ABI_NAMESPACE(_V2)
/** @addtogroup diagnostics
* @{
*/
namespace __adl_only
{
void make_error_code() = delete;
void make_error_condition() = delete;
}
/** Class error_code
*
* This class is a value type storing an integer error number and a
* category that gives meaning to the error number. Typically this is done
* close the the point where the error happens, to capture the original
* error value.
*
* An `error_code` object can be used to store the original error value
* emitted by some subsystem, with a category relevant to the subsystem.
* For example, errors from POSIX library functions can be represented by
* an `errno` value and the "generic" category, but errors from an HTTP
* library might be represented by an HTTP response status code (e.g. 404)
* and a custom category defined by the library.
*
* @headerfile system_error
* @since C++11
*/
class error_code
{
template<typename _ErrorCodeEnum>
using _Check
= __enable_if_t<is_error_code_enum<_ErrorCodeEnum>::value>;
public:
error_code() noexcept
: _M_value(0), _M_cat(&system_category()) { }
error_code(int __v, const error_category& __cat) noexcept
: _M_value(__v), _M_cat(&__cat) { }
/// Initialize with a user-defined type, by calling make_error_code.
template<typename _ErrorCodeEnum,
typename = _Check<_ErrorCodeEnum>>
error_code(_ErrorCodeEnum __e) noexcept
{
using __adl_only::make_error_code;
*this = make_error_code(__e);
}
error_code(const error_code&) = default;
error_code& operator=(const error_code&) = default;
void
assign(int __v, const error_category& __cat) noexcept
{
_M_value = __v;
_M_cat = &__cat;
}
void
clear() noexcept
{ assign(0, system_category()); }
/// The error value.
[[__nodiscard__]]
int
value() const noexcept { return _M_value; }
/// The error category that this error belongs to.
[[__nodiscard__]]
const error_category&
category() const noexcept { return *_M_cat; }
/// An `error_condition` for this error's category and value.
error_condition
default_error_condition() const noexcept;
/// The category's description of the value.
_GLIBCXX_DEFAULT_ABI_TAG
string
message() const
{ return category().message(value()); }
/// Test whether `value()` is non-zero.
[[__nodiscard__]]
explicit operator bool() const noexcept
{ return _M_value != 0; }
// DR 804.
private:
int _M_value;
const error_category* _M_cat;
};
// C++11 19.5.2.5 non-member functions
/** Create an `error_code` representing a standard `errc` condition.
*
* The `std::errc` constants correspond to `errno` macros and so use the
* generic category.
*
* @relates error_code
* @since C++11
*/
[[__nodiscard__]]
inline error_code
make_error_code(errc __e) noexcept
{ return error_code(static_cast<int>(__e), generic_category()); }
/** Ordered comparison for std::error_code.
*
* This defines a total order by comparing the categories, and then
* if they are equal comparing the values.
*
* @relates error_code
* @since C++11
*/
#if __cpp_lib_three_way_comparison
[[nodiscard]]
inline strong_ordering
operator<=>(const error_code& __lhs, const error_code& __rhs) noexcept
{
if (auto __c = __lhs.category() <=> __rhs.category(); __c != 0)
return __c;
return __lhs.value() <=> __rhs.value();
}
#else
inline bool
operator<(const error_code& __lhs, const error_code& __rhs) noexcept
{
return (__lhs.category() < __rhs.category()
|| (__lhs.category() == __rhs.category()
&& __lhs.value() < __rhs.value()));
}
#endif
/** Write a std::error_code to an ostream.
*
* @relates error_code
* @since C++11
*/
template<typename _CharT, typename _Traits>
basic_ostream<_CharT, _Traits>&
operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
{ return (__os << __e.category().name() << ':' << __e.value()); }
/** Class error_condition
*
* This class represents error conditions that may be visible at an API
* boundary. Different `error_code` values that can occur within a library
* or module might map to the same `error_condition`.
*
* An `error_condition` represents something that the program can test for,
* and subsequently take appropriate action.
*
* @headerfile system_error
* @since C++11
*/
class error_condition
{
template<typename _ErrorConditionEnum>
using _Check
= __enable_if_t<is_error_condition_enum<_ErrorConditionEnum>::value>;
public:
/// Initialize with a zero (no error) value and the generic category.
error_condition() noexcept
: _M_value(0), _M_cat(&generic_category()) { }
/// Initialize with the specified value and category.
error_condition(int __v, const error_category& __cat) noexcept
: _M_value(__v), _M_cat(&__cat) { }
/// Initialize with a user-defined type, by calling make_error_condition.
template<typename _ErrorConditionEnum,
typename = _Check<_ErrorConditionEnum>>
error_condition(_ErrorConditionEnum __e) noexcept
{
using __adl_only::make_error_condition;
*this = make_error_condition(__e);
}
error_condition(const error_condition&) = default;
error_condition& operator=(const error_condition&) = default;
/// Set the value and category.
void
assign(int __v, const error_category& __cat) noexcept
{
_M_value = __v;
_M_cat = &__cat;
}
/// Reset the value and category to the default-constructed state.
void
clear() noexcept
{ assign(0, generic_category()); }
// C++11 19.5.3.4 observers
/// The error value.
[[__nodiscard__]]
int
value() const noexcept { return _M_value; }
/// The error category that this error belongs to.
[[__nodiscard__]]
const error_category&
category() const noexcept { return *_M_cat; }
/// The category's description of the value.
_GLIBCXX_DEFAULT_ABI_TAG
string
message() const
{ return category().message(value()); }
/// Test whether `value()` is non-zero.
[[__nodiscard__]]
explicit operator bool() const noexcept
{ return _M_value != 0; }
// DR 804.
private:
int _M_value;
const error_category* _M_cat;
};
// C++11 19.5.3.5 non-member functions
/** Create an `error_condition` representing a standard `errc` condition.
*
* The `std::errc` constants correspond to `errno` macros and so use the
* generic category.
*
* @relates error_condition
* @since C++11
*/
[[__nodiscard__]]
inline error_condition
make_error_condition(errc __e) noexcept
{ return error_condition(static_cast<int>(__e), generic_category()); }
// C++11 19.5.4 Comparison operators
/** Equality comparison for std::error_code.
*
* Returns true only if they have the same category and the same value.
*
* @relates error_condition
* @since C++11
*/
[[__nodiscard__]]
inline bool
operator==(const error_code& __lhs, const error_code& __rhs) noexcept
{
return __lhs.category() == __rhs.category()
&& __lhs.value() == __rhs.value();
}
/** Equality comparison for std::error_code and std::error_condition.
*
* Uses each category's `equivalent` member function to check whether
* the values correspond to an equivalent error in that category.
*
* @relates error_condition
* @since C++11
*/
[[__nodiscard__]]
inline bool
operator==(const error_code& __lhs, const error_condition& __rhs) noexcept
{
return __lhs.category().equivalent(__lhs.value(), __rhs)
|| __rhs.category().equivalent(__lhs, __rhs.value());
}
/** Equality comparison for std::error_condition.
*
* Returns true only if they have the same category and the same value.
*
* @relates error_condition
* @since C++11
*/
[[__nodiscard__]]
inline bool
operator==(const error_condition& __lhs,
const error_condition& __rhs) noexcept
{
return __lhs.category() == __rhs.category()
&& __lhs.value() == __rhs.value();
}
/** Ordered comparison for std::error_condition.
*
* This defines a total order by comparing the categories, and then
* if they are equal comparing the values.
*
* @relates error_condition
* @since C++11
*/
#if __cpp_lib_three_way_comparison
[[nodiscard]]
inline strong_ordering
operator<=>(const error_condition& __lhs,
const error_condition& __rhs) noexcept
{
if (auto __c = __lhs.category() <=> __rhs.category(); __c != 0)
return __c;
return __lhs.value() <=> __rhs.value();
}
#else
inline bool
operator<(const error_condition& __lhs,
const error_condition& __rhs) noexcept
{
return (__lhs.category() < __rhs.category()
|| (__lhs.category() == __rhs.category()
&& __lhs.value() < __rhs.value()));
}
/// @relates error_condition
inline bool
operator==(const error_condition& __lhs, const error_code& __rhs) noexcept
{
return (__rhs.category().equivalent(__rhs.value(), __lhs)
|| __lhs.category().equivalent(__rhs, __lhs.value()));
}
/// @relates error_code
inline bool
operator!=(const error_code& __lhs, const error_code& __rhs) noexcept
{ return !(__lhs == __rhs); }
/// @relates error_code
inline bool
operator!=(const error_code& __lhs, const error_condition& __rhs) noexcept
{ return !(__lhs == __rhs); }
/// @relates error_condition
inline bool
operator!=(const error_condition& __lhs, const error_code& __rhs) noexcept
{ return !(__lhs == __rhs); }
/// @relates error_condition
inline bool
operator!=(const error_condition& __lhs,
const error_condition& __rhs) noexcept
{ return !(__lhs == __rhs); }
#endif // three_way_comparison
/// @}
/**
* @brief An exception type that includes an `error_code` value.
*
* Typically used to report errors from the operating system and other
* low-level APIs.
*
* @headerfile system_error
* @since C++11
* @ingroup exceptions
*/
class system_error : public std::runtime_error
{
private:
error_code _M_code;
public:
system_error(error_code __ec = error_code())
: runtime_error(__ec.message()), _M_code(__ec) { }
system_error(error_code __ec, const string& __what)
: runtime_error(__what + (": " + __ec.message())), _M_code(__ec) { }
system_error(error_code __ec, const char* __what)
: runtime_error(__what + (": " + __ec.message())), _M_code(__ec) { }
system_error(int __v, const error_category& __ecat, const char* __what)
: system_error(error_code(__v, __ecat), __what) { }
system_error(int __v, const error_category& __ecat)
: runtime_error(error_code(__v, __ecat).message()),
_M_code(__v, __ecat) { }
system_error(int __v, const error_category& __ecat, const string& __what)
: runtime_error(__what + (": " + error_code(__v, __ecat).message())),
_M_code(__v, __ecat) { }
#if __cplusplus >= 201103L
system_error (const system_error &) = default;
system_error &operator= (const system_error &) = default;
#endif
virtual ~system_error() noexcept;
const error_code&
code() const noexcept { return _M_code; }
};
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#include <bits/functional_hash.h>
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
#ifndef _GLIBCXX_COMPATIBILITY_CXX0X
// DR 1182.
/// std::hash specialization for error_code.
/// @relates error_code
template<>
struct hash<error_code>
: public __hash_base<size_t, error_code>
{
size_t
operator()(const error_code& __e) const noexcept
{
const size_t __tmp = std::_Hash_impl::hash(__e.value());
return std::_Hash_impl::__hash_combine(&__e.category(), __tmp);
}
};
#endif // _GLIBCXX_COMPATIBILITY_CXX0X
#if __cplusplus >= 201703L
// DR 2686.
/// std::hash specialization for error_condition.
/// @relates error_condition
template<>
struct hash<error_condition>
: public __hash_base<size_t, error_condition>
{
size_t
operator()(const error_condition& __e) const noexcept
{
const size_t __tmp = std::_Hash_impl::hash(__e.value());
return std::_Hash_impl::__hash_combine(&__e.category(), __tmp);
}
};
#endif
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // C++11
#endif // _GLIBCXX_SYSTEM_ERROR
compare
iosfwd
stdexcept
functional_hash.h
requires_hosted.h
c++0x_warning.h
error_constants.h
c++config.h
std::error_condition::operator==
bool operator==(const error_condition &__lhs, const error_condition &__rhs) noexcept
Definition system_error:482
std::generic_category
const error_category & generic_category() noexcept
Error category for errno error codes.
std::error_code::operator<=>
strong_ordering operator<=>(const error_code &__lhs, const error_code &__rhs) noexcept
Definition system_error:318
std::error_condition::operator==
bool operator==(const error_code &__lhs, const error_condition &__rhs) noexcept
Definition system_error:467
std::error_condition::operator<=>
strong_ordering operator<=>(const error_condition &__lhs, const error_condition &__rhs) noexcept
Definition system_error:500
std::error_code::make_error_code
error_code make_error_code(errc __e) noexcept
Definition system_error:304
std::error_condition::operator==
bool operator==(const error_code &__lhs, const error_code &__rhs) noexcept
Definition system_error:451
std::error_condition::make_error_condition
error_condition make_error_condition(errc __e) noexcept
Definition system_error:437
std::system_category
const error_category & system_category() noexcept
Error category for other error codes defined by the OS.
std::make_error_condition
error_condition make_error_condition(future_errc __errc) noexcept
Overload of make_error_condition for future_errc.
Definition future:103
std::make_error_code
error_code make_error_code(future_errc __errc) noexcept
Overload of make_error_code for future_errc.
Definition future:97
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:119
std::false_type
__bool_constant< false > false_type
The type used as a compile-time boolean with false value.
Definition type_traits:122
std
ISO C++ entities toplevel namespace is std.
std::operator<<
std::basic_ostream< _CharT, _Traits > & operator<<(std::basic_ostream< _CharT, _Traits > &__os, const bitset< _Nb > &__x)
Global I/O operators for bitsets.
Definition bitset:1754
std::hash
Primary class template hash.
Definition functional_hash.h:106
std::is_error_code_enum
is_error_code_enum
Definition system_error:64
std::is_error_condition_enum
is_error_condition_enum
Definition system_error:68
std::error_category
Definition system_error:109
std::error_category::equivalent
virtual bool equivalent(int __i, const error_condition &__cond) const noexcept
Test whether cond corresponds to i for this category.
std::error_category::equivalent
virtual bool equivalent(const error_code &__code, int __i) const noexcept
Test whether code corresponds to i for this category.
std::error_category::operator==
bool operator==(const error_category &__other) const noexcept
An error_category only compares equal to itself.
Definition system_error:162
std::error_category::name
virtual const char * name() const noexcept=0
A string that identifies the error category.
std::error_category::default_error_condition
virtual error_condition default_error_condition(int __i) const noexcept
Return an error_condition corresponding to i in this category.
std::error_category::operator<=>
strong_ordering operator<=>(const error_category &__rhs) const noexcept
Ordered comparison that defines a total order for error categories.
Definition system_error:169
std::error_category::message
virtual string message(int) const =0
A description of the error condition corresponding to the number.
std::error_code
Definition system_error:226
std::error_code::category
const error_category & category() const noexcept
The error category that this error belongs to.
Definition system_error:268
std::error_code::value
int value() const noexcept
The error value.
Definition system_error:263
std::error_code::message
string message() const
The category's description of the value.
Definition system_error:277
std::error_code::default_error_condition
error_condition default_error_condition() const noexcept
An error_condition for this error's category and value.
std::error_condition
Definition system_error:357
std::error_condition::category
const error_category & category() const noexcept
The error category that this error belongs to.
Definition system_error:405
std::error_condition::value
int value() const noexcept
The error value.
Definition system_error:400
std::error_condition::error_condition
error_condition() noexcept
Initialize with a zero (no error) value and the generic category.
Definition system_error:363
std::error_condition::message
string message() const
The category's description of the value.
Definition system_error:410
std::error_condition::assign
void assign(int __v, const error_category &__cat) noexcept
Set the value and category.
Definition system_error:384
std::error_condition::clear
void clear() noexcept
Reset the value and category to the default-constructed state.
Definition system_error:392
std::system_error
An exception type that includes an error_code value.
Definition system_error:559
std::runtime_error
One of two subclasses of exception.
Definition stdexcept_except.h:454
std::runtime_error::runtime_error
runtime_error(const string &__arg)
std::less
One of the comparison functors.
Definition stl_function.h:404