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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c++
Subject: Re: Which exception for a buffer overrun?
Date: Wed, 16 Oct 2019 15:34:52 -0700
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Paavo Helde <myfirstname@osa.pri.ee> writes:
> On 16.10.2019 0:59, Soviet_Mario wrote:
>> One thing I really can't stand is the way C used to share a single
>> variable (errno) to store status, that may be overwritten unpredictably
>
> It's not a single variable, it's a single variable per thread.

Right.  The standard says errno is a macro "which expands to a
modifiable lvalue that has type int and thread local storage duration,
the value of which is set to a positive error number by several library
functions".

On my system, the errno macro expands to
    (*__errno_location ())
where the __errno_location function presumably returns a pointer to a
thread-local int object.

This was introduced in C11.  In C90 and C99, thread local storage did
not exist, but implementations could do something equivalent.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Will write code for food.
void Void(void) { Void(); } /* The recursive call of the void */