C 中的 ASM 给出错误 -std=c99

发布于 2024-07-17 08:16:35 字数 540 浏览 5 评论 0原文

我现在愿意使用 -std=c99 编译我的项目，但我遇到了一个我暂时无法理解的错误。这一行：

my_type* td = ({ register kmy_type* arg0 asm("eax"); arg0; });

仅在 C99 中给我以下错误：

warning: ISO C forbids nested functions
error: syntax error before ‘asm’
error: ‘arg0’ undeclared (first use in this function)
error: (Each undeclared identifier is reported only once
error: for each function it appears in.)
warning: ISO C forbids braced-groups within expressions

欢迎任何线索来帮助我理解这意味着什么。我没有写这行，我也不确定它的目的是什么。

原文

I'm now willing to compile my project with -std=c99 and I'm facing an error I'm not understanding for the moment. This line :

my_type* td = ({ register kmy_type* arg0 asm("eax"); arg0; });

gives me the following error only in C99 :

warning: ISO C forbids nested functions
error: syntax error before ‘asm’
error: ‘arg0’ undeclared (first use in this function)
error: (Each undeclared identifier is reported only once
error: for each function it appears in.)
warning: ISO C forbids braced-groups within expressions

Any clues are welcome to help me understanding what this means. I didn't write this line and I'm also not sure to understand what is its purpose.

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沩ん囻菔务 2024-07-24 08:16:36

该行

my_type* td = ({ register my_type* arg0 asm("eax"); arg0; });

应该在 eax 寄存器中获取一个值，该值被解释为指向 td 变量的指针。然而，它使用了大量的 GNU 扩展，特别是语句表达式和 asm（显式寄存器分配）的使用。我建议您切换到 -std=gnu99 （或任何名称）。否则，您可能想使用双下划线（例如 asm -> __asm）或 __extension__ 关键字，但我不这样做知道它在 c99 模式下是否有帮助。

编辑：我刚刚尝试过，只需将 asm 更改为 __asm 即可。

The line

my_type* td = ({ register my_type* arg0 asm("eax"); arg0; });

should get a value in the eax register, interpreted as a pointer, into td variable. However, it uses lots of GNU extensions, particularly statement expressions and this use of asm (explicit register allocation). I'd suggest you to switch to -std=gnu99 (or whatever it's called). Otherwise, you might want to play with double underscores (eg. asm -> __asm) or the __extension__ keyword, but I don't know if it'll help in c99 mode.

Edit: I just tried it and simply changing asm to __asm works.

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