[syserr.syserr]

# 19 Diagnostics library [[diagnostics]](./#diagnostics)

## 19.5 System error support [[syserr]](syserr#syserr)

### 19.5.8 Class system_error [syserr.syserr]

#### [19.5.8.1](#overview) Overview [[syserr.syserr.overview]](syserr.syserr.overview)

[1](#overview-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1518)

The class system_error describes an exception object used to
report error conditions that have an associated error code[.](#overview-1.sentence-1)

Such error
conditions typically originate from the operating system or other low-level
application program interfaces[.](#overview-1.sentence-2)

[2](#overview-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1524)

[*Note [1](#overview-note-1)*:

If an error represents an out-of-memory condition, implementations are
encouraged to throw an exception object of type [bad_alloc](bad.alloc "17.6.4.1 Class bad_­alloc [bad.alloc]") rather
than system_error[.](#overview-2.sentence-1)

— *end note*]

[🔗](#lib:system_error)

namespace std {class system_error : public runtime_error {public: system_error(error_code ec, const string& what_arg);
 system_error(error_code ec, const char* what_arg);
 system_error(error_code ec);
 system_error(int ev, const error_category& ecat, const string& what_arg);
 system_error(int ev, const error_category& ecat, const char* what_arg);
 system_error(int ev, const error_category& ecat); const error_code& code() const noexcept; const char* what() const noexcept override; };}

#### [19.5.8.2](#members) Members [[syserr.syserr.members]](syserr.syserr.members)

[🔗](#lib:system_error,constructor)

`system_error(error_code ec, const string& what_arg);
`

[1](#members-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1555)

*Postconditions*: code() == ec and  
string_view(what()).find(what_arg.c_str()) != string_view​::​npos[.](#members-1.sentence-1)

[🔗](#lib:system_error,constructor_)

`system_error(error_code ec, const char* what_arg);
`

[2](#members-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1567)

*Postconditions*: code() == ec andstring_view(what()).find(what_arg) != string_view​::​npos[.](#members-2.sentence-1)

[🔗](#lib:system_error,constructor__)

`system_error(error_code ec);
`

[3](#members-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1579)

*Postconditions*: code() == ec[.](#members-3.sentence-1)

[🔗](#lib:system_error,constructor___)

`system_error(int ev, const error_category& ecat, const string& what_arg);
`

[4](#members-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1590)

*Postconditions*: code() == error_code(ev, ecat) and  
string_view(what()).find(what_arg.c_str()) != string_view​::​npos[.](#members-4.sentence-1)

[🔗](#lib:system_error,constructor____)

`system_error(int ev, const error_category& ecat, const char* what_arg);
`

[5](#members-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1602)

*Postconditions*: code() == error_code(ev, ecat) and  
string_view(what()).find(what_arg) != string_view​::​npos[.](#members-5.sentence-1)

[🔗](#lib:system_error,constructor_____)

`system_error(int ev, const error_category& ecat);
`

[6](#members-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1614)

*Postconditions*: code() == error_code(ev, ecat)[.](#members-6.sentence-1)

[🔗](#lib:code,system_error)

`const error_code& code() const noexcept;
`

[7](#members-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1625)

*Returns*: ec or error_code(ev, ecat), from the constructor,
as appropriate[.](#members-7.sentence-1)

[🔗](#lib:what,system_error)

`const char* what() const noexcept override;
`

[8](#members-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/diagnostics.tex#L1637)

*Returns*: An ntbs incorporating the arguments supplied in the constructor[.](#members-8.sentence-1)

[*Note [1](#members-note-1)*:

The returned ntbs might be the contents of what_arg + ": " + code.message()[.](#members-8.sentence-2)

— *end note*]