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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.std.c
Subject: Re: Add @ to basic character set?
Date: Mon, 07 Dec 2020 12:19:48 -0800
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Thomas David Rivers <rivers@dignus.com> writes:
> Philipp Klaus Krause wrote:
>
>>I wonder if it would make sense to add @ to the basic character set.
>>Virtually everyone is using it in comments and strings already anyway
>>(for email addresses), and I don't see anything preventing
>>implementations from supporting it, as it is available in both ASCII and
>>common EBCDIC code pages:
>>
>>http://www.colecovision.eu/stuff/proposal-basic-@.html
>>  
> Just to add to the "used as an extension" list of compilers; the Dignus
> compilers (and the SAS/C compilers) for the mainframe use @ to be similar
> to &, except that it can accept an rvalue.   If an rvalue is present
> after a @, then the address of a copy is generated.  The copy is
> declared within
> the inner-most scope.
>
> This is helpful in some situations on the mainframe where pass-by-reference
> is the norm, as in:
>
>   FOO(@1, @2);
>
> (where FOO is defined in some other language, e.g. PL/I, where the
> parameters
> are pass-by-reference.)

You can do the same thing with a compound literal starting in C99:

#include <stdio.h>

void FOO(int *a, int *b) {
    printf("%d %d\n", *a, *b);
}

int main(void) {
    FOO(&(int){1}, &(int){2});
}

I suspect the extension predates compound literals.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips Healthcare
void Void(void) { Void(); } /* The recursive call of the void */