{"type":"doc","content":[{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"总述"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":" "},{"type":"text","text":"宏的使用，大家经常会用，但是一般只是简单定义一个符号常量，类似于#define WHEEL_SCALE_MM 0.53f、"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"#define LOG_I(tag, text_fmt, ...) log_i(tag, text_fmt, ##__VA_ARGS__) ，但是除此之外还有宏还有个##粘贴作用，可以配合#define这个常量表达式，可以做成一个宏定义指针函数列表，继而查询执行函数。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 话不多说，我们开始今天的分享，首先还是会进行一下常规的描述，再分享\"##\"粘贴的妙用。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"作者：良知犹存"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"转载授权以及围观：欢迎添加微信公众号：羽林君"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"一、#define的常规操作"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/aa/aab546cccfd9c47bce4d0f1f27f8f9ff.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" #define预处理器指令和其他预处理器指令一样， 以#号作为一行的开"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"始。ANSI和后来的标准都允许#号前面有空格或制表符， 而且还允许在#和"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"指令的其余部分之间有空格。但是旧版本的C要求指令从一行最左边开始，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而且#和指令其余部分之间不能有空格。指令可以出现在源文件的任何地"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"方， 其定义从指令出现的地方到该文件末尾有效。我们大量使用#define指令来定义明示常量（manifest constant） （也叫做符号常量） 。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 预处理器指令从#开始运行， 到后面的第1个换行符为止。也就是说， 指"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"令的长度仅限于一行。然而， 在预处理开始前， 编译器会把多行物理行处理为一行逻辑行。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"一般我们会用#define 来进行明示常量，或者做一个简单的宏替换函数"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define RX_BUF_SIZE 30#define MBEDTLS_DES_C /*数据加密*/\n#define ExitIsr Encoder_Isr \nvoid Encoder_Isr(void){ \n\tg.dir_count += (g.dir == 1)? 1 : -1;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 每行#define（逻辑行） 都由3部分组成。第1部分是#define指令本身。第"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2部分是选定的缩写， 也称为宏。有些宏代表值（如本例） ， 这些宏被称为"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"类对象宏 。C 语言还有类函数宏 ， 稍后讨论。宏的名称中不允许有空格， 而且必须遵循C变量的命名规则：只能使用字符、 数字和下划线（_） 字符， 而且首字符不能是数字。第3部分（指令行的其余部分） 称为替换列表或替换体 。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 一旦预处理器在程序中找到宏的实例后， 就会用替换体代替该宏。从宏变成最终替换文本的过程称为宏展开。注意， 可以在#define行使用标准C注释。如前所述， 每条注释都会被一个空格代替。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/81/811dbb499649f701ea3d1f9123b26efd.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"此外我们还会比较多的使用变宏参"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过把宏参数列表中最后的参数写成省略号（即， 3个点...） 来实现这"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"一功能。这样， 预定义宏_ _VA_ARGS_ _可用在替换部分中， 表明省略号代表什么。 "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define PR(...) printf(_ _VA_ARGS_ _)\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"假设稍后调用该宏："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"PR(\"Howdy\");PR(\"weight = %d, shipping = $%.2f\\n\", wt, sp);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"对于第1次调用， _ _VA_ARGS_ _展开为1个参数：\"Howdy\"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"对于第2次调用， _ _VA_ARGS_ _展开为3个参数：\"weight = %d,"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"shipping = $%.2f\\n\"、 wt、 sp。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"因此， 展开后的代码是："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"printf(\"Howdy\");printf(\"weight = %d, shipping = $%.2f\\n\", wt, sp);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"二、#define配合##使用"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/aa/aab546cccfd9c47bce4d0f1f27f8f9ff.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 很多人应该都知道\"##\"的用法，它被称为预处理的粘合剂，与#运算符类似，##运算符可用于类函数宏的替换部分。而且，##还可以用于对象宏的替换部分。##运算符可以把两个记号组合成一个记号。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define def_u32_array(__name, __size) uint32_t array_##__name[__size];"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"实际中，我们可以这样使用："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"def_u32_array(sample_buffer, 64)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"宏展开的效果是："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"uint32_t array_sample_buffer[64];"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"同样类比于初始化一个数组，我们也可以粘贴形成一个函数"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面就是在Linux内核里面的源代码："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其中这个__pcpu_size_call_return宏，通过##粘贴选择要使用的raw_cpu_read_x 函数。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define __pcpu_size_call_return(stem, variable) \\\n({ \\\n typeof(variable) pscr_ret__; \\\n __verify_pcpu_ptr(&(variable)); \\\n switch(sizeof(variable)) { \\\n case 1: pscr_ret__ = stem##1(variable); break; \\\n case 2: pscr_ret__ = stem##2(variable); break; \\\n case 4: pscr_ret__ = stem##4(variable); break; \\\n case 8: pscr_ret__ = stem##8(variable); break; \\\n default: \\\n __bad_size_call_parameter(); break; \\\n } \\\n pscr_ret__; \\\n})\n#define raw_cpu_read_1(pcp) raw_cpu_generic_read(pcp)\n#define raw_cpu_generic_read(pcp) \\\n({ \\\n *raw_cpu_ptr(&(pcp)); \\\n})"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这部分是更高层次的宏定义，将##粘贴的函数再次定义为一个宏函数"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define raw_cpu_read(pcp) __pcpu_size_call_return(raw_cpu_read_, pcp)\n#define __this_cpu_read(pcp) \\\n({ \\\n __this_cpu_preempt_check(\"read\"); \\\n raw_cpu_read(pcp); \\\n})"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最后面进行执行 __this_cpu_read(current_kprobe);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"int __kprobes arc_kprobe_handler(unsigned long addr, struct pt_regs *regs)\n{\n struct kprobe *p\n p = __this_cpu_read(current_kprobe);\n p = get_kprobe((unsigned long *)addr);\n \n ... 省略多行代码\n \n if (p->break_handler && p->break_handler(p, regs)) {\n setup_singlestep(p, regs);\n kcb->kprobe_status = KPROBE_HIT_SS;\n return 1;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在C++中我们也可以将做成一个指针列表，对应好每个函数的名称后，再次调用该定义的宏参数，就实现了指针调用。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define AddFunc(Func) \\\nFuncPtrTemplate Func##Map(int mode_name, int state_name) \\\n{ \\\n static auto modeMap = Func##Register(); \\\n auto pair = std::make_pair(mode_name, state_name); \\\n auto mapEntry = modeMap->find(pair); \\\n if (mapEntry == modeMap->end()) \\\n return nullptr; \\\n return mapEntry->second; \\\n} \\\nbool Mode::Func(State *state) { \\\n auto state_id = getStateId(); \\\n auto p_function = Func##Map(getId(), state_id); \\\n if (p_function) \\\n return p_function(this, state); \\\n return false; \\\n}\nAddFunc(IsExit);\nint main(){\n IsExit(p.get());\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这也是Linux内核中的代码，用来print不同状态的打印信息，如果大家想要快速掌握这些使用方法，建议大家撸一撸Linux内核源码呢。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/9f/9f2bbf50f548385e100ed0ea3393d2e0.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 这就是我分享的#define的操作方法，里面代码是实践过的，如果大家有什么更好的思路，欢迎分享交流哈。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"—"},{"type":"text","marks":[{"type":"italic"}],"text":"END"},{"type":"text","text":"—"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"推荐阅读"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【1】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247491648&idx=1&sn=523ffec9bc089bf41a4a146dfe0cb610&chksm=e90ce1acde7b68baecf4ed9e7a997801ac48939a1d0e72167e692c4cceca0a5a65ef9fa76dba&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"c++nullptr（空指针常量）、constexpr（常量表达式）"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzUxMjEyNDgyNw==&mid=2247487776&idx=1&sn=6f41a0b12195e1a8c808a9d317dd132e&chksm=f96863d4ce1feac277bc0218ea9f7f65754b0e652c8543149df598f4c8ef87f3e1646de0de4c&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"【2】"}]},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247483803&idx=1&sn=1cbc72c1985965c052c374eb627d4446&chksm=e90f0077de788961258f46eed6149498f6f7c907b8da4a2090ada295158bec3b46c2a9b628a6&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"嵌入式底层开发的软件框架简述"}]},{"type":"text","text":" "},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzUxMjEyNDgyNw==&mid=2247488626&idx=1&sn=c9c045382502de4417a48cf63fffc691&chksm=f9686686ce1fef90b096ddbf70129785b8e0b9666a3367e706364543ea81d728b61323747e2f&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"必读"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【3】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247489695&idx=1&sn=d7dd58878070d34a6ee3a21be035e6e1&chksm=e90f1973de789065101b678830244790e06a19318162765327e6d0103a01b7d2a11827643956&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"CPU中的程序是怎么运行起来的"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【4】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247490441&idx=1&sn=3be088b25663c72ba43d3f42f916acf5&chksm=e90f1a65de78937331e9beb61f463d332c705b086b763d04f027bcda2c68b655c34d1c66f9e6&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"C++的匿名函数（lambda表达式）"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【5】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247490871&idx=1&sn=c0fb6e8303302247b3a08c4b16acc4bd&chksm=e90f1cdbde7895cdcdf789e7056a6295cbdffc05cd1272f78450d5cbbdf62bc3edee995d3e92&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"阶段性文章总结分析"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本公众号全部原创干货已整理成一个目录，后台回复【资源】即可获得。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}
你用过宏##粘贴函数，然后用函数指针查找执行吗？今天就给你说道说道
{"type":"doc","content":[{"type":"blockquote","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"总述"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":" "},{"type":"text","text":"宏的使用，大家经常会用，但是一般只是简单定义一个符号常量，类似于#define WHEEL_SCALE_MM 0.53f、"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"#define LOG_I(tag, text_fmt, ...) log_i(tag, text_fmt, ##__VA_ARGS__) ，但是除此之外还有宏还有个##粘贴作用，可以配合#define这个常量表达式，可以做成一个宏定义指针函数列表，继而查询执行函数。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 话不多说，我们开始今天的分享，首先还是会进行一下常规的描述，再分享\"##\"粘贴的妙用。"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"作者：良知犹存"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"转载授权以及围观：欢迎添加微信公众号：羽林君"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"一、#define的常规操作"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/aa/aab546cccfd9c47bce4d0f1f27f8f9ff.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" #define预处理器指令和其他预处理器指令一样， 以#号作为一行的开"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"始。ANSI和后来的标准都允许#号前面有空格或制表符， 而且还允许在#和"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"指令的其余部分之间有空格。但是旧版本的C要求指令从一行最左边开始，"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而且#和指令其余部分之间不能有空格。指令可以出现在源文件的任何地"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"方， 其定义从指令出现的地方到该文件末尾有效。我们大量使用#define指令来定义明示常量（manifest constant） （也叫做符号常量） 。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 预处理器指令从#开始运行， 到后面的第1个换行符为止。也就是说， 指"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"令的长度仅限于一行。然而， 在预处理开始前， 编译器会把多行物理行处理为一行逻辑行。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"一般我们会用#define 来进行明示常量，或者做一个简单的宏替换函数"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define RX_BUF_SIZE 30#define MBEDTLS_DES_C /*数据加密*/\n#define ExitIsr Encoder_Isr \nvoid Encoder_Isr(void){ \n\tg.dir_count += (g.dir == 1)? 1 : -1;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 每行#define（逻辑行） 都由3部分组成。第1部分是#define指令本身。第"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2部分是选定的缩写， 也称为宏。有些宏代表值（如本例） ， 这些宏被称为"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"类对象宏 。C 语言还有类函数宏 ， 稍后讨论。宏的名称中不允许有空格， 而且必须遵循C变量的命名规则：只能使用字符、 数字和下划线（_） 字符， 而且首字符不能是数字。第3部分（指令行的其余部分） 称为替换列表或替换体 。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 一旦预处理器在程序中找到宏的实例后， 就会用替换体代替该宏。从宏变成最终替换文本的过程称为宏展开。注意， 可以在#define行使用标准C注释。如前所述， 每条注释都会被一个空格代替。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/81/811dbb499649f701ea3d1f9123b26efd.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"此外我们还会比较多的使用变宏参"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通过把宏参数列表中最后的参数写成省略号（即， 3个点...） 来实现这"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"一功能。这样， 预定义宏_ _VA_ARGS_ _可用在替换部分中， 表明省略号代表什么。 "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define PR(...) printf(_ _VA_ARGS_ _)\n"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"假设稍后调用该宏："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"PR(\"Howdy\");PR(\"weight = %d, shipping = $%.2f\\n\", wt, sp);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"对于第1次调用， _ _VA_ARGS_ _展开为1个参数：\"Howdy\"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"对于第2次调用， _ _VA_ARGS_ _展开为3个参数：\"weight = %d,"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"shipping = $%.2f\\n\"、 wt、 sp。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"因此， 展开后的代码是："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"printf(\"Howdy\");printf(\"weight = %d, shipping = $%.2f\\n\", wt, sp);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"二、#define配合##使用"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/aa/aab546cccfd9c47bce4d0f1f27f8f9ff.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 很多人应该都知道\"##\"的用法，它被称为预处理的粘合剂，与#运算符类似，##运算符可用于类函数宏的替换部分。而且，##还可以用于对象宏的替换部分。##运算符可以把两个记号组合成一个记号。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define def_u32_array(__name, __size) uint32_t array_##__name[__size];"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"实际中，我们可以这样使用："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"def_u32_array(sample_buffer, 64)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"宏展开的效果是："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"uint32_t array_sample_buffer[64];"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"同样类比于初始化一个数组，我们也可以粘贴形成一个函数"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面就是在Linux内核里面的源代码："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其中这个__pcpu_size_call_return宏，通过##粘贴选择要使用的raw_cpu_read_x 函数。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define __pcpu_size_call_return(stem, variable) \\\n({ \\\n typeof(variable) pscr_ret__; \\\n __verify_pcpu_ptr(&(variable)); \\\n switch(sizeof(variable)) { \\\n case 1: pscr_ret__ = stem##1(variable); break; \\\n case 2: pscr_ret__ = stem##2(variable); break; \\\n case 4: pscr_ret__ = stem##4(variable); break; \\\n case 8: pscr_ret__ = stem##8(variable); break; \\\n default: \\\n __bad_size_call_parameter(); break; \\\n } \\\n pscr_ret__; \\\n})\n#define raw_cpu_read_1(pcp) raw_cpu_generic_read(pcp)\n#define raw_cpu_generic_read(pcp) \\\n({ \\\n *raw_cpu_ptr(&(pcp)); \\\n})"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这部分是更高层次的宏定义，将##粘贴的函数再次定义为一个宏函数"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define raw_cpu_read(pcp) __pcpu_size_call_return(raw_cpu_read_, pcp)\n#define __this_cpu_read(pcp) \\\n({ \\\n __this_cpu_preempt_check(\"read\"); \\\n raw_cpu_read(pcp); \\\n})"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最后面进行执行 __this_cpu_read(current_kprobe);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"int __kprobes arc_kprobe_handler(unsigned long addr, struct pt_regs *regs)\n{\n struct kprobe *p\n p = __this_cpu_read(current_kprobe);\n p = get_kprobe((unsigned long *)addr);\n \n ... 省略多行代码\n \n if (p->break_handler && p->break_handler(p, regs)) {\n setup_singlestep(p, regs);\n kcb->kprobe_status = KPROBE_HIT_SS;\n return 1;\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在C++中我们也可以将做成一个指针列表，对应好每个函数的名称后，再次调用该定义的宏参数，就实现了指针调用。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"#define AddFunc(Func) \\\nFuncPtrTemplate Func##Map(int mode_name, int state_name) \\\n{ \\\n static auto modeMap = Func##Register(); \\\n auto pair = std::make_pair(mode_name, state_name); \\\n auto mapEntry = modeMap->find(pair); \\\n if (mapEntry == modeMap->end()) \\\n return nullptr; \\\n return mapEntry->second; \\\n} \\\nbool Mode::Func(State *state) { \\\n auto state_id = getStateId(); \\\n auto p_function = Func##Map(getId(), state_id); \\\n if (p_function) \\\n return p_function(this, state); \\\n return false; \\\n}\nAddFunc(IsExit);\nint main(){\n IsExit(p.get());\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"这也是Linux内核中的代码，用来print不同状态的打印信息，如果大家想要快速掌握这些使用方法，建议大家撸一撸Linux内核源码呢。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/9f/9f2bbf50f548385e100ed0ea3393d2e0.png","alt":"","title":null,"style":null,"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":""}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":" 这就是我分享的#define的操作方法，里面代码是实践过的，如果大家有什么更好的思路，欢迎分享交流哈。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"italic"},{"type":"strong"}],"text":"—"},{"type":"text","marks":[{"type":"italic"}],"text":"END"},{"type":"text","text":"—"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"推荐阅读"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【1】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247491648&idx=1&sn=523ffec9bc089bf41a4a146dfe0cb610&chksm=e90ce1acde7b68baecf4ed9e7a997801ac48939a1d0e72167e692c4cceca0a5a65ef9fa76dba&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"c++nullptr（空指针常量）、constexpr（常量表达式）"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzUxMjEyNDgyNw==&mid=2247487776&idx=1&sn=6f41a0b12195e1a8c808a9d317dd132e&chksm=f96863d4ce1feac277bc0218ea9f7f65754b0e652c8543149df598f4c8ef87f3e1646de0de4c&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"【2】"}]},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247483803&idx=1&sn=1cbc72c1985965c052c374eb627d4446&chksm=e90f0077de788961258f46eed6149498f6f7c907b8da4a2090ada295158bec3b46c2a9b628a6&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"嵌入式底层开发的软件框架简述"}]},{"type":"text","text":" "},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzUxMjEyNDgyNw==&mid=2247488626&idx=1&sn=c9c045382502de4417a48cf63fffc691&chksm=f9686686ce1fef90b096ddbf70129785b8e0b9666a3367e706364543ea81d728b61323747e2f&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"必读"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【3】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247489695&idx=1&sn=d7dd58878070d34a6ee3a21be035e6e1&chksm=e90f1973de789065101b678830244790e06a19318162765327e6d0103a01b7d2a11827643956&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"CPU中的程序是怎么运行起来的"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【4】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247490441&idx=1&sn=3be088b25663c72ba43d3f42f916acf5&chksm=e90f1a65de78937331e9beb61f463d332c705b086b763d04f027bcda2c68b655c34d1c66f9e6&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"C++的匿名函数（lambda表达式）"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"【5】"},{"type":"link","attrs":{"href":"http://mp.weixin.qq.com/s?__biz=MzI0MTI2MDY3NQ==&mid=2247490871&idx=1&sn=c0fb6e8303302247b3a08c4b16acc4bd&chksm=e90f1cdbde7895cdcdf789e7056a6295cbdffc05cd1272f78450d5cbbdf62bc3edee995d3e92&scene=21#wechat_redirect","title":null},"content":[{"type":"text","text":"阶段性文章总结分析"}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本公众号全部原创干货已整理成一个目录，后台回复【资源】即可获得。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}
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