### 20.10 `auto` and `register` ¶

For historical reasons, you can write `auto` or `register` before a local variable declaration. `auto` merely emphasizes that the variable isn’t static; it changes nothing.

`register` suggests to the compiler storing this variable in a register. However, GNU C ignores this suggestion, since it can choose the best variables to store in registers without any hints.

It is an error to take the address of a variable declared `register`, so you cannot use the unary ‘`&`’ operator on it. If the variable is an array, you can’t use it at all (other than as the operand of `sizeof`), which makes it rather useless.