How is scope of variable implemented in compiler at machine level or memory level

Question

How is scope of a variable is implemented by compilers? I mean, when we say static variable, the scope is limited to the block or functions that defined in the same file where the static variable is defined? How is this achieved in machine level or at memory level?

How actually is this restriction achieved?

How is this scoping resolved at program run time?

Answer 1

It is not achieved at all at the machine level. The compiler checks for scopes before machine code is actually generated. The rules of C are implemented by the compiler, not by the machine. The compiler must check those rules, the machine does not and cannot.

A very simplistic explanation of how the compiler checks this:

Whenever a scope is introduced, the compiler gives it a name and puts it in a structure (a tree) that makes it easy to determine the position of that scope in relation to other scopes, and it is marked as being the current scope. When a variable is declared, its assigned to the current scope. When accessing a variable, it is looked for in the current scope. If not found, the tree is looked up to find the scope above the current one. This continues until we reach the topmost scope. If the variable is still not found, then we have a scope violation.

Answer 2

inside compilers, its implementation defined. For example if I were writing a compiler, I would use a tree to define 'scope' and it would definitely be a symbol table inside a binary tree.

Some would use an arbitrary depth Hash table. Its all implementation defined.