19 Diagnostics library [diagnostics]

19.4 Error numbers [errno]

19.4.1 General [errno.general]

1
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The contents of the header <cerrno> are the same as the POSIX header <errno.h>, except that errno shall be defined as a macro.
[Note 1: 
The intent is to remain in close alignment with the POSIX standard.
— end note]
A separate errno value is provided for each thread.