GNU C Family Extensions

Some time ago I met confusing C ternary operator usage

return timeout ?: 1;

It turned out to be a GNU "Conditionals with Omitted Operands" 

C extension. The list of "Extensions to the C Language Family" can be found here.

This page is worth reading. For example, getting

the address of a label defined in the current function (or a containing
function) with the unary operator `&&'. The value has type void *. This value
is a constant and can be used wherever a constant of that type is valid.
For example:

     void *ptr;
     /* ... */
     ptr = &&foo;

To use these values, you need to be able to jump to one. This is done with
the computed goto statement, goto *exp;.
For example,

     goto *ptr;