可以将代码块用作C宏的参数吗? [英] Is it OK to use a code block as an argument for a C macro?

问题描述

我的模式基本上是一些样板代码，中间部分有所不同

I have a pattern that is basically some boilerplate code with a part that varies in the middle

if(condition){
    struct Foo m = start_stuff();
    { m.foo = bar(1,2); m.baz = 17; } //this part varies
    end_stuff();
}

可以使中间代码块作为参数的宏指令吗? C语言中的宏扩展规则似乎非常复杂，因此我不确定将来是否会遇到任何麻烦的情况(特别是我不理解如果我的代码如何分隔宏参数)里面有逗号).

Is it OK to make a macro taht takes that intermediate code block as an argument? The rules for macro expansion in C seem awfully complicated so I am not sure if there aren't any corner cases that could come and bite me in the future (in particular, I don't understand how the macro arguments are separated if my code has commas in it).

#define MY_MACRO(typ, do_stuff) do { \
    if(condition){ \
        struct typ m = start_stuff(); \
        do_stuff; \
        end_stuff(); \
    } \
}while(0)

//usage
MY_MACRO(Foo, {
   m.foo = bar(1,2);
   m.baz = 17;
});

到目前为止，我唯一想到的是，如果我在宏中使用循环语句，则会捕获break和continue，这对于我的特定用例来说是可以接受的折衷.

So far the only thing that I managed to think of is break and continue getting captured if I use looping statements in my macro and that would be an acceptable tradeoff for my particular use case.

当然，如果可以的话，我会使用一个函数.我在此问题中使用的示例经过了简化，没有展示仅适用于宏魔术的部分.

edit: Of course, I would have used a functions if I could. The example I used in this question is simplified and doesn't showcase the bits that can only work with macro magic.

推荐答案

您可以将代码块放入宏参数中，前提是它没有不加保护的逗号.在您的示例中，参数中唯一的逗号受到保护，因为它用括号括起来.

You can put a code block into a macro argument provided that it has no unguarded comma. In your example, the only comma in the argument is guarded because it is surrounded by parentheses.

请注意，仅 括号用逗号括起来.括号([])和花括号({})不在.

Note that only parentheses guard commas. Brackets ([]) and braces ({}) do not.

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