c - 下面的c 宏声明是什么意思？

Question

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Answer 1

它是 Stringification operator :

The # operator (known as the "Stringification Operator") converts a token into a string, escaping any quotes or backslashes appropriately.

Example:

#define str(s) #s

str(p = "foo\n";) // outputs "p = \"foo\\n\";"
str(\n)           // outputs "\n"

If you want to stringify the expansion of a macro argument, you have to use two levels of macros:

#define xstr(s) str(s)
#define str(s) #s
#define foo 4

str (foo)  // outputs "foo"
xstr (foo) // outputs "4"

最后一个示例中的代码与问题中的代码非常接近。请注意，正如 @KeithThompson 提到的，“以两个下划线开头，或一个下划线后跟一个大写字母的标识符是保留的”。