宏中参数前面有 # 标记

发布于 2024-09-11 22:04:33 字数 296 浏览 8 评论 0原文

#define LINK_ENTITY_TO_CLASS(mapClassName,DLLClassName) \
    static CEntityFactory<DLLClassName> mapClassName( #mapClassName );

这是来自 Half-Life 2 Alien Swarm mod 的宏，旨在使用 MSVC 进行编译。

我以前从未在宏中见过以 # 开头的参数，并且我不确定这是否是 MSVC 特有的东西或只是不常见。这是什么意思？

原文

#define LINK_ENTITY_TO_CLASS(mapClassName,DLLClassName) \
    static CEntityFactory<DLLClassName> mapClassName( #mapClassName );

This is a macro from the Alien Swarm mod for Half-Life 2, meant to be compiled with MSVC.

I've never seen an argument preceded by a # in a macro before, and I'm not sure if this is a MSVC specific thing or just uncommon. What does it mean?

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荭秂 2024-09-18 22:04:33

这是标准 C 和 C++ 的一部分，并且不是特定于实现的。 # 预处理运算符将其参数字符串化。它采用传入宏的任何标记作为其操作数指定的参数（在本例中为参数mapClassName），并从中生成字符串文字。因此，举一个简单的例子，

#define STRINGIZE(x) # x

STRINGIZE(Hello World)
// gets replaced with
"Hello World"

请注意，参数标记在字符串化之前不会被宏替换，因此如果 Hello 或 World 被定义为一个宏，结果仍然是一样的。您需要使用额外的间接级别来替换参数宏（该链接的答案讨论了连接运算符 ##，但同样适用于字符串化运算符。

This is part of both standard C and C++ and is not implementation-specific. The # preprocessing operator stringizes its argument. It takes whatever tokens were passed into the macro for the parameter designated by its operand (in this case, the parameter mapClassName) and makes a string literal out of them. So, for a simple example,

#define STRINGIZE(x) # x

STRINGIZE(Hello World)
// gets replaced with
"Hello World"

Note that the argument tokens are not macro replaced before they are stringized, so if Hello or World were defined as a macro, the result would still be the same. You need to use an extra level of indirection to get the arguments macro replaced (that linked answer discusses the concatenation operator, ##, but applies equally to the stringization operator.

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