Can scopes be wrapped in parentheses and return a value in C? [duplicate]

Question

I looked up the definition of MIN on Mac OS X and found this:

#define MIN(A,B) ({ __typeof__(A) __a = (A); __typeof__(B) __b = (B); __a < __b ? __a : __b; })

It's not so obvious at first, but when it expands, it turns into something that looks extremely strange to me:

int a = 1, b = 2;
// int min = MIN(a, b);
int min = ({
    int __a = (a);
    int __b = (b);
    __a < __b ? __a : __b;
});

This is, indeed, a scope wrapped into an expression that "returns" the value of the last expression. It seems to work, at least with clang, with pretty much arbitrary code inside the scope:

int a = ({
    time_t x = time(NULL);
    if (x % 3 == 1)
        x++;

    x % 10;
});

I had never seen this before, and I was wondering if it's standard. I know for a fact that Visual Studio won't accept it, but then again, Visual Studio is stuck with C89, so that's not very telling.

Answer 1

This is a GCC extension to standard C called Statement Expressions. Yes, you can use it if you only need to support GNU compilers (and it is cross-platform). If you need to stick to standard C, you won't use the notation.