c - "unix"是 C 中的受限关键字吗？

Question

此代码无法在 GCC 版本 4.3.2 (Debian 4.3.2-1.1) 上为我编译

main() {
  int unix;
}

我检查了 C 关键字列表，“unix”不在其中之一。

为什么会出现以下错误？

unix.c:2: error: expected identifier or ‘(’ before numeric constant

Answer 1

unix 不是标准保留的标识符。

如果您使用 -std=c89 或 -std=c99 进行编译，gcc 编译器将按照您的预期接受该程序。

来自 gcc 手册(https://gcc.gnu.org/onlinedocs/cpp/System-specific-Predefined-Macros.html)，重点是我的。

... However, historically system-specific macros have had names with no special prefix; for instance, it is common to find unix defined on Unix systems. For all such macros, GCC provides a parallel macro with two underscores added at the beginning and the end. If unix is defined, __unix__ will be defined too. There will never be more than two underscores; the parallel of _mips is __mips__.