osx man page for tcl_errnomsg

Tcl_SetErrno(3) 					      Tcl Library Procedures						   Tcl_SetErrno(3)

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NAME
       Tcl_SetErrno, Tcl_GetErrno, Tcl_ErrnoId, Tcl_ErrnoMsg - manipulate errno to store and retrieve error codes

SYNOPSIS
       #include <tcl.h>

       void
       Tcl_SetErrno(errorCode)

       int
       Tcl_GetErrno()

       const char *
       Tcl_ErrnoId()

       const char *
       Tcl_ErrnoMsg(errorCode)

ARGUMENTS
       int errorCode (in)	   A POSIX error code such as ENOENT.
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DESCRIPTION
       Tcl_SetErrno  and Tcl_GetErrno provide portable access to the errno variable, which is used to record a POSIX error code after system calls
       and other operations such as Tcl_Gets.  These procedures are necessary because global variable accesses cannot be made across module bound-
       aries on some platforms.

       Tcl_SetErrno  sets  the	errno  variable to the value of the errorCode argument C procedures that wish to return error information to their
       callers via errno should call Tcl_SetErrno rather than setting errno directly.

       Tcl_GetErrno returns the current value of errno.  Procedures wishing to access errno should call this procedure instead of accessing  errno
       directly.

       Tcl_ErrnoId and Tcl_ErrnoMsg return string representations of errno values.  Tcl_ErrnoId returns a machine-readable textual identifier such
       as "EACCES" that corresponds to the current value of errno.  Tcl_ErrnoMsg returns a human-readable string such as "permission denied"  that
       corresponds  to	the value of its errorCode argument.  The errorCode argument is typically the value returned by Tcl_GetErrno.  The strings
       returned by these functions are statically allocated and the caller must not free or modify them.

KEYWORDS
       errno, error code, global variables

Tcl									8.3							   Tcl_SetErrno(3)