使用前的 C 声明

Question

C 中的所有标识符在使用前都需要声明，但我找不到它在 C99 标准中表示的位置。

我觉得也是指宏定义，不过定义的只是宏展开顺序。

Answer 1

C99:TC3 6.5.1 §2，脚注 79 明确指出:

Thus, an undeclared identifier is a violation of the syntax.

结合 6.2.1 §5:

Unless explicitly stated otherwise, [...] it [ie an identifier] refers to the entity in the relevant name space whose declaration is visible at the point the identifier occurs.

和§7:

[...] Any other identifier has scope that begins just after the completion of its declarator.