What's this syntax called? Is it standard C? Is it standard C++?

Question

int x = ({
    int y = 10, z;
    if (2>1) {
        z = 11;
    }
    y+z;
});

x will be 21. What is this syntax? I've seen it in C and I'm guessing it also exists in C++. Is this standard in either language?

This is neither nor: [**Demo on coliru**](http://coliru.stacked-crooked.com/a/a3a5decee7792137) I checked whether I missed something exotic but I didn't. — Scheff's Cat, Jan 21 '21 at 16:40
I looks a little bit like a failed attempt for an initialization with an immediately called [lambda](https://en.cppreference.com/w/cpp/language/lambda). — Scheff's Cat, Jan 21 '21 at 16:41
@SamVarshavchik interesting, can you elaborate? online g++ compiler refused. — SergeyA, Jan 21 '21 at 16:41
Even with the extension, I don't see how it would compile as `z` is out of scope where it is used. — Fred Larson, Jan 21 '21 at 16:43
@SamVarshavchik I'm happy that OP asked for _standart_. :-) (So, I at least didn't write something wrong...) — Scheff's Cat, Jan 21 '21 at 16:43
@SamVarshavchik quite interesting indeed, care to add an answer? — SergeyA, Jan 21 '21 at 16:43
The last statement in the inner block is evaluated, and the result is used. Mentally insert `return` at the beginning of the last statement in there, and it will become crystal clear. — Sam Varshavchik, Jan 21 '21 at 16:43
Using any programming language you can write program in Fortran. — Slava, Jan 21 '21 at 16:45

score 6 · Answer 1 · answered Jan 21 '21 at 16:45

6

This is a non-standard gcc compiler extension, that lets arbitrary code get executed in an expression context and produce an expression result.

answered Jan 21 '21 at 16:45

Sam Varshavchik

1

I doubt even this extension would allow to use variable out of scope. – Slava Jan 21 '21 at 16:47
Yes, this part is true. But, the overall syntax is what it is. – Sam Varshavchik Jan 21 '21 at 16:47
In fact, removing `-pedantic` (and fixing the issue with `z`), the complaints go away in gcc as well as g++: [**Demo on coliru**](http://coliru.stacked-crooked.com/a/4aa51b02c8f942a4) – Scheff's Cat Jan 21 '21 at 16:50

1 Answers1