《Linux 高级程序设计（第三版）》——1.4 Linux下编码风格

xiaoxiao2023-07-08 167

本节书摘来自异步社区《Linux 高级程序设计（第三版）》一书中的第1章，第1.4节，作者：杨宗德 , 吕光宏 , 刘雍著，更多章节内容可以访问云栖社区“异步社区”公众号查看

1.4 Linux下编码风格

Linux 高级程序设计（第三版）下面为读者列出GNU编码规范和Linux内核编码规范示例。

1.4.1　GNU编码规范下面是GNU emacs中的一段代码。

/* Interface from Emacs to terminfo. Copyright (C) 1985, 1986 Free Software Foundation, Inc. This file is part of GNU Emacs. GNU Emacs is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Emacs is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Emacs; see the file COPYING. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include <config.h> #include "lisp.h" /* Define these variables that serve as global parameters to termcap, so that we do not need to conditionalize the places in Emacs that set them. */ char *UP, *BC, PC; /* Interface to curses/terminfo library. Turns out that all of the terminfo-level routines look like their termcap counterparts except for tparm, which replaces tgoto. Not only is the calling sequence different, but the string format is different too.*/ char *tparam (string, outstring, len, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9) char *string; char *outstring; int arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9; { char *temp; extern char *tparm(); temp = tparm (string, arg1, arg2, arg3, arg4, arg5, arg6, arg7, arg8, arg9); if (outstring == 0) outstring = ((char *) (xmalloc ((strlen (temp)) + 1))); strcpy (outstring, temp); return outstring; }

分析上面的代码可以看出GNU具有如下编码风格。

函数开头的左花括号放到最左边，避免把任何其他的左花括号、左括号或者左方括号放到最左边。尽力避免让两个不同优先级的操作符出现在相同的对齐方式中。每个程序开头都应该有一段简短的说明其功能的注释。例如GNU emacs上面的代码中的注释。每个函数都加上注释，以说明函数做了些什么，需要哪些种类的参数，参数可能值的含义以及用途。不要跨行声明多个变量。在每一行中都以一个新的声明开头。当在一个if语句中嵌套了另一个if-else语句时，应用花括号把if-else括起来。要在同一个声明中同时说明结构标识和变量，或者结构标识和类型定义（typedef）。尽量避免在if的条件中进行赋值。在名字中使用下划线以分隔单词，尽量使用小写；在宏或者枚举中通常使用大写常量。使用一个命令行选项时，给出的变量应该在选项含义的说明之后，而不是选项字符之后。另外，Linux有很多工具来帮助程序员养成良好编码规范。除了vim和emacs以外，还有indent工具可以帮程序员美化C/C++源代码。下面用这条命令可将Linux内核编程风格的程序quan.c转变为GNU编程风格。

[root@localhost ～]#$ indent -gnu quan.c1.4.2　Linux内核编码规范下面是Linux内核2.6.13目录archi386kernel中的numaq.c的节选代码，现在并不要求读懂此代码，而是看Linux的内核编程风格。

/* * Written by: Patricia Gaughen, IBM Corporation * * Copyright (C) 2002, IBM Corp. * * All rights reserved. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or * NON INFRINGEMENT. See the GNU General Public License for more * details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. * * Send feedback to <gone@us.ibm.com> */ #include <linux/config.h> #include <linux/mm.h> #include <linux/bootmem.h> #include <linux/mmzone.h> #include <linux/module.h> #include <linux/nodemask.h> #include <asm/numaq.h> #include <asm/topology.h> #include <asm/processor.h> #define MB_TO_PAGES(addr) ((addr) << (20 - PAGE_SHIFT)) /* * Function: smp_dump_qct() * * Description: gets memory layout from the quad config table. This * function also updates node_online_map with the nodes (quads) present. */ static void __init smp_dump_qct(void) { int node; struct eachquadmem *eq; struct sys_cfg_data *scd = (struct sys_cfg_data *)__va(SYS_CFG_DATA_PRIV_ADDR); nodes_clear(node_online_map); for_each_node(node) { if (scd->quads_present31_0 & (1 << node)) { node_set_online(node); eq = &scd->eq[node]; /* Convert to pages */ node_start_pfn[node] = MB_TO_PAGES( eq->hi_shrd_mem_start - eq->priv_mem_size); node_end_pfn[node] = MB_TO_PAGES( eq->hi_shrd_mem_start + eq->hi_shrd_mem_size); memory_present(node, node_start_pfn[node], node_end_pfn[node]); node_remap_size[node] = node_memmap_size_bytes(node, node_start_pfn[node], node_end_pfn[node]); } } }

分析以上代码可以看出Linux内核代码具有如下风格。

缩进采用tab制表符。在if或者for循环中，将开始的大括号放在一行的最后，而将结束大括号放在本段语句结束行的第一位，函数中的大括号除外。变量命名尽量使用简短的名字，简写或者单词间采用了_隔开，比如代码中的sys_cfg_data。函数最好短小精悍，一个函数最好只做一件事情，而且函数中的变量一般不超过10个，大小一般都小于80行。一个模块的注释一般注明了作者、版权、注释说明代码的功能，而不是说明其实现原理，这也和Linux的文化有关。以上是GNU编码风格和Linux内核编码风格，两种风格体现着两种不同的文化精神，有些地方相似，有些地方迥然不同，但是目的只有一个：形成一个清晰、美观、可维护、方便扩展的代码。读者可以根据个人情况选择其中一种编码规范来编写自己的程序。