More information on `({});` in C?

Question

I\'ve noticed that sometimes, C macros are written as something like this:

#define foo(bar) ({ ++bar; })

After some experimentation, I\'ve

Answer 1

This is a GNU extension called statement expressions.

When declaring macros in standard-C, you often see do...while(0) loops used for similar purposes (ie creating a block scope). A statement expression is superior to the loop hack because it can return a value. If you want to do something similar in standard-C, you'd have to define an additional function and lose the convenience of lexical scoping.