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cppdraft/value/error/codes.md

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+[value.error.codes]
+
+# 16 Library introduction [[library]](./#library)
+
+## 16.4 Library-wide requirements [[requirements]](requirements#value.error.codes)
+
+### 16.4.6 Conforming implementations [[conforming]](conforming#value.error.codes)
+
+#### 16.4.6.16 Value of error codes [value.error.codes]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L3969)
+
+Certain functions in the C++ standard library report errors via aerror_code ([[syserr.errcode.overview]](syserr.errcode.overview "19.5.4.1 Overview")) object[.](#1.sentence-1)
+
+That object'scategory() member shall return system_category() for
+errors originating from the operating system, or a reference to animplementation-defined error_category object for errors originating elsewhere[.](#1.sentence-2)
+
+The implementation shall define the possible values of value() for each of these
+error categories[.](#1.sentence-3)
+
+[*Example [1](#example-1)*:
+
+For operating systems that are based on POSIX,
+implementations should define the std​::​system_category() values as
+identical to the POSIX errno values, with additional values as defined by the
+operating system's documentation[.](#1.sentence-4)
+
+Implementations for operating systems that are not
+based on POSIX should define values identical to the operating system's
+values[.](#1.sentence-5)
+
+For errors that do not originate from the operating system, the implementation
+may provide enums for the associated values[.](#1.sentence-6)
+
+— *end example*]