[syserr.errcode] # 19 Diagnostics library [[diagnostics]](./#diagnostics) ## 19.5 System error support [[syserr]](syserr#errcode) ### 19.5.4 Class error_code [syserr.errcode] #### [19.5.4.1](#overview) Overview [[syserr.errcode.overview]](syserr.errcode.overview) [1](#overview-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1009) The class error_code describes an object used to hold error code values, such as those originating from the operating system or other low-level application program interfaces[.](#overview-1.sentence-1) [*Note [1](#overview-note-1)*: Class error_code is an adjunct to error reporting by exception[.](#overview-1.sentence-2) — *end note*] [🔗](#lib:error_code) namespace std {class error_code {public:// [[syserr.errcode.constructors]](#constructors "19.5.4.2 Constructors"), constructors error_code() noexcept; error_code(int val, const error_category& cat) noexcept; template error_code(ErrorCodeEnum e) noexcept; // [[syserr.errcode.modifiers]](#modifiers "19.5.4.3 Modifiers"), modifiersvoid assign(int val, const error_category& cat) noexcept; template error_code& operator=(ErrorCodeEnum e) noexcept; void clear() noexcept; // [[syserr.errcode.observers]](#observers "19.5.4.4 Observers"), observersint value() const noexcept; const error_category& category() const noexcept; error_condition default_error_condition() const noexcept; string message() const; explicit operator bool() const noexcept; private:int *val_*; // *exposition only*const error_category* *cat_*; // *exposition only*}; // [[syserr.errcode.nonmembers]](#nonmembers "19.5.4.5 Non-member functions"), non-member functions error_code make_error_code(errc e) noexcept; template basic_ostream&operator<<(basic_ostream& os, const error_code& ec);} #### [19.5.4.2](#constructors) Constructors [[syserr.errcode.constructors]](syserr.errcode.constructors) [🔗](#lib:error_code,constructor) `error_code() noexcept; ` [1](#constructors-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1064) *Effects*: Initializes *val_* with 0 and *cat_* with &system_category()[.](#constructors-1.sentence-1) [🔗](#lib:error_code,constructor_) `error_code(int val, const error_category& cat) noexcept; ` [2](#constructors-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1076) *Effects*: Initializes *val_* with val and *cat_* with &cat[.](#constructors-2.sentence-1) [🔗](#lib:error_code,constructor__) `template error_code(ErrorCodeEnum e) noexcept; ` [3](#constructors-3) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1089) *Constraints*: [is_error_code_enum_v](system.error.syn#lib:is_error_code_enum_v "19.5.2 Header synopsis [system.error.syn]") is true[.](#constructors-3.sentence-1) [4](#constructors-4) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1093) *Effects*: Equivalent to:error_code ec = make_error_code(e); assign(ec.value(), ec.category()); #### [19.5.4.3](#modifiers) Modifiers [[syserr.errcode.modifiers]](syserr.errcode.modifiers) [🔗](#lib:assign,error_code) `void assign(int val, const error_category& cat) noexcept; ` [1](#modifiers-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1110) *Postconditions*: *val_* == val and *cat_* == &cat[.](#modifiers-1.sentence-1) [🔗](#lib:operator=,error_code) `template error_code& operator=(ErrorCodeEnum e) noexcept; ` [2](#modifiers-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1122) *Constraints*: [is_error_code_enum_v](system.error.syn#lib:is_error_code_enum_v "19.5.2 Header synopsis [system.error.syn]") is true[.](#modifiers-2.sentence-1) [3](#modifiers-3) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1126) *Effects*: Equivalent to:error_code ec = make_error_code(e); assign(ec.value(), ec.category()); [4](#modifiers-4) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1134) *Returns*: *this[.](#modifiers-4.sentence-1) [🔗](#lib:clear,error_code) `void clear() noexcept; ` [5](#modifiers-5) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1145) *Postconditions*: value() == 0 and category() == system_category()[.](#modifiers-5.sentence-1) #### [19.5.4.4](#observers) Observers [[syserr.errcode.observers]](syserr.errcode.observers) [🔗](#lib:value,error_code) `int value() const noexcept; ` [1](#observers-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1159) *Returns*: *val_*[.](#observers-1.sentence-1) [🔗](#lib:category,error_code) `const error_category& category() const noexcept; ` [2](#observers-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1170) *Returns*: **cat_*[.](#observers-2.sentence-1) [🔗](#lib:default_error_condition,error_code) `error_condition default_error_condition() const noexcept; ` [3](#observers-3) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1181) *Returns*: category().default_error_condition(value())[.](#observers-3.sentence-1) [🔗](#lib:message,error_code) `string message() const; ` [4](#observers-4) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1192) *Returns*: category().message(value())[.](#observers-4.sentence-1) [🔗](#lib:operator_bool,error_code) `explicit operator bool() const noexcept; ` [5](#observers-5) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1203) *Returns*: value() != 0[.](#observers-5.sentence-1) #### [19.5.4.5](#nonmembers) Non-member functions [[syserr.errcode.nonmembers]](syserr.errcode.nonmembers) [🔗](#lib:make_error_code,errc) `error_code make_error_code(errc e) noexcept; ` [1](#nonmembers-1) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1216) *Returns*: error_code(static_cast(e), generic_category())[.](#nonmembers-1.sentence-1) [🔗](#lib:operator%3c%3c,error_code) `template basic_ostream& operator<<(basic_ostream& os, const error_code& ec); ` [2](#nonmembers-2) [#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1228) *Effects*: Equivalent to: return os << ec.category().name() << ':' << ec.value();