Can the address of a variable with automatic storage duration be taken in its definition?

Question

Is it allowed to take the address of an object on the right hand-side of its definition, as happens in foo() below:

typedef struct { char x[100]         


        

Answer 1

6.2.1 Scopes of identifiers

7. Structure, union, and enumeration tags have scope that begins just after the appearance of the tag in a type specifier that declares the tag. Each enumeration constant has scope that begins just after the appearance of its defining enumerator in an enumerator list. Any other identifier has scope that begins just after the completion of its declarator.

In

chars b = make(&b);
//    ^^

the declarator is b, so it is in scope in its own initializer.

6.2.4 Storage durations of objects

6. For such an [automatic] object that does not have a variable length array type, its lifetime extends from entry into the block with which it is associated until execution of that block ends in any way.

So in

{ // X
  chars b = make(&b);
}

the lifetime of b starts at X, so by the time the initializer executes, it is both alive and in scope.

As far as I can tell, this is effectively identical to

{
  chars b;
  b = make(&b);
}

There's no reason you couldn't use &b there.