c - 在#if 指令之前强制宏定义

Question

我惊讶地发现未定义的宏在预处理器表达式中使用时会自动分配 0 值。例如:

//#define A
#if A == 0
// do something
#endif

这段代码将在“做某事”部分编译，而我预计它会给出一个错误。我发现 GCC 有一个 option to warn against this case :

• Identifiers that are not macros, which are all considered to be the number zero. This allows you to write #if MACRO instead of #ifdef MACRO, if you know that MACRO, when defined, will always have a nonzero value. Function-like macros used without their function call parentheses are also treated as zero.

  In some contexts this shortcut is undesirable. The -Wundef option causes GCC to warn whenever it encounters an identifier which is not a macro in an #if.

因此，我正在为 IAR Embedded Workbench IDE 寻找与 -Wundef 等效的选项。有这样的选择吗？

Answer 1

IAR Embedded Workbench 中的 IAR C/C++ 编译器可以检测到这一点。但是，默认情况下它被配置为未显示的备注。

您可以使用命令行选项 --remarks，或者使用 --diag_warning=Pe193 或 将严重性提高到警告或错误--diag_error=Pe193.