最重要的一条规则编写代码时最重要的一条规则是：检查周围的代码并尝试模仿它。 作为维护人员，如果收到的补丁明显与周围代码的编码风格不同，这是令人沮丧的。这是不尊重人的，就像某人穿着泥泞的鞋子走进一间一尘不染的房子。 因此，无论本文推荐的是什么，如果已经编写了代码并且您正在对其进行修补，请保持其当前的样式一致，即使它不是您最喜欢的样式。 一般规则这里列出了最明显和最重要的一般规则。在你继续阅读其他章节之前，请仔细检查它们。 - 使用C99标准
- 不使用制表符，而是使用空格
- 每个缩进级别使用4个空格
- 在关键字和左括号之间使用一个空格
- 在函数名和左括号之间不要使用空格
int32_t a = sum(4, 3); /* OK */int32_t a = sum (4, 3); /* Wrong */
- 不要在变量/函数/宏/类型中使用_或前缀。这是为C语言本身保留的
- 对于严格的模块私有函数，使用prv_ name前缀
- 对于包含下划线_ char的变量/函数/宏/类型，只能使用小写字母
- 左花括号总是与关键字(for, while, do, switch, if，…)在同一行
size_t i;for (i = 0; i < 5; ++i) { /* OK */}for (i = 0; i < 5; ++i){ /* Wrong */}for (i = 0; i < 5; ++i) /* Wrong */{}
// 微信公众号：嵌入式大杂烩int32_t a;a = 3 + 4; /* OK */for (a = 0; a < 5; ++a) /* OK */a=3+4; /* Wrong */a = 3+4; /* Wrong */for (a=0;a<5;++a) /* Wrong */
// 微信公众号：嵌入式大杂烩func_name(5, 4); /* OK */func_name(4,3); /* Wrong */
- 不要初始化静态和全局变量为0(或NULL)，让编译器为您做
static int32_t a; /* OK */static int32_t b = 4; /* OK */static int32_t a = 0; /* Wrong */voidmy_func(void) { static int32_t* ptr;/* OK */ static char abc = 0;/* Wrong */}
voidmy_func(void) { char a; /* OK */ char b; /* Wrong, variable with char type already exists */ char a, b; /* OK */}
i.自定义结构和枚举 ii.整数类型，更宽的无符号类型优先 iii.单/双浮点 intmy_func(void) { /* 1 */ my_struct_t my; /* First custom structures */ my_struct_ptr_t* p; /* Pointers too */ /* 2 */ uint32_t a; int32_t b; uint16_t c; int16_t g; char h; /* ... */ /* 3 */ double d; float f;}
- 总是在块的开头声明局部变量，在第一个可执行语句之前
- 在for循环中声明计数器变量
/* OK */for (size_t i = 0; i < 10; ++i)/* OK, if you need counter variable later */size_t i;for (i = 0; i < 10; ++i) { if (...) { break; }}if (i == 10) {}/* Wrong */size_t i;for (i = 0; i < 10; ++i) ...
voida(void) { /* Avoid function calls when declaring variable */ int32_t a, b = sum(1, 2); /* Use this */ int32_t a, b; b = sum(1, 2); /* This is ok */ uint8_t a = 3, b = 4;}
- 除了char、float或double之外，始终使用stdint.h标准库中声明的类型。例如，8位的uint8_t等
- 不要使用stdbool.h库。分别使用1或0表示真或假
/* OK */uint8_t status;status = 0;/* Wrong */#include <stdbool.h>bool status = true;
- 永远不要与真实相比较。例如，使用if(check_func()){…}替换if (check_func() == 1)
- 总是将指针与空值进行比较
void* ptr;/* ... *//* OK, compare against NULL */if (ptr == NULL || ptr != NULL) {}/* Wrong */if (ptr || !ptr) {}
int32_t a = 0;...a++; /* Wrong */++a; /* OK */for (size_t j = 0; j < 10; ++j) {} /* OK */
- 总是使用size_t作为长度或大小变量
- 如果函数不应该修改指针所指向的内存，则总是使用const作为指针
- 如果不应该修改函数的形参或变量，则总是使用const
/* When d could be modified, data pointed to by d could not be modified */voidmy_func(const void* d) {}/* When d and data pointed to by d both could not be modified */voidmy_func(const void* const d) {}/* Not required, it is advised */voidmy_func(const size_t len) {}/* When d should not be modified inside function, only data pointed to by d could be modified */voidmy_func(void* const d) {}
- 当函数可以接受任何类型的指针时，总是使用void *，不要使用uint8_t *。函数在实现时必须注意正确的类型转换
/* * To send data, function should not modify memory pointed to by `data` variable * thus `const` keyword is important * * To send generic data (or to write them to file) * any type may be passed for data, * thus use `void *` *//* OK example */voidsend_data(const void* data, size_t len) { /* OK */ /* Do not cast `void *` or `const void *` */ const uint8_t* d = data;/* Function handles proper type for internal usage */}voidsend_data(const void* data, int len) { /* Wrong, not not use int */}
- 总是使用括号和sizeof操作符
- 不要使用变长数组。使用动态内存分配代替标准C malloc和自由函数，或者如果库/项目提供了自定义内存分配，使用它的实现看看LwMEM，一个自定义内存管理库。
/* OK */#include <stdlib.h>voidmy_func(size_t size) { int32_t* arr; arr = malloc(sizeof(*arr) * n); /* OK, Allocate memory */ arr = malloc(sizeof *arr * n); /* Wrong, brackets for sizeof operator are missing */ if (arr == NULL) { /* FAIL, no memory */ } free(arr); /* Free memory after usage */}/* Wrong */voidmy_func(size_t size) { int32_t arr[size]; /* Wrong, do not use VLA */}
- 总是将variable与0进行比较，除非它被视为布尔类型
- 永远不要将布尔处理的变量与0或1进行比较。用NOT(!)代替
size_t length = 5; /* Counter variable */uint8_t is_ok = 0; /* Boolean-treated variable */if (length) /* Wrong, length is not treated as boolean */if (length > 0) /* OK, length is treated as counter variable containing multi values, not only 0 or 1 */if (length == 0) /* OK, length is treated as counter variable containing multi values, not only 0 or 1 */if (is_ok) /* OK, variable is treated as boolean */if (!is_ok) /* OK, -||- */if (is_ok == 1) /* Wrong, never compare boolean variable against 1! */if (is_ok == 0) /* Wrong, use ! for negative check */
- 对于注释，总是使用/* comment */，即使是单行注释
- 在头文件中总是包含带有extern关键字的c++检查
- 每个函数都必须包含doxygen-enabled注释，即使函数是静态的
- 使用英文名称/文本的函数，变量，注释
- 变量使用小写字母
- 如果变量包含多个名称，请使用下划线。force_redraw。不要使用forceRedraw
- 对于C标准库的包含文件，请始终使用<和>。例如，# include < stdlib.h >
- 对于自定义库，请始终使用''。例如，# include“my_library.h”
- 当转换为指针类型时，总是将星号与类型对齐，例如。uint8_t* t = (uint8_t*)var_width_diff_type
- 始终尊重项目或库中已经使用的代码风格
注释- 不允许以//开头的注释。总是使用/* comment */，即使是单行注释
//This is comment (wrong)/* This is comment (ok) */
/* * This is multi-line comments, * written in 2 lines (ok) *//** * Wrong, use double-asterisk only for doxygen documentation *//** Single line comment without space before asterisk (wrong)*//* * Single line comment in multi-line configuration (wrong) *//* Single line comment (ok) */
- 注释时使用12个缩进(12 * 4个空格)偏移量。如果语句大于12个缩进，将注释4-空格对齐(下面的例子)到下一个可用缩进
voidmy_func(void) { char a, b; a = call_func_returning_char_a(a); /* This is comment with 12*4 spaces indent from beginning of line */ b = call_func_returning_char_a_but_func_name_is_very_long(a); /* This is comment, aligned to 4-spaces indent */}
函数- 每个可以从模块外部访问的函数都必须包含函数原型(或声明)
- 函数名必须小写，可以用下划线_分隔
/* OK */void my_func(void);void myfunc(void);/* Wrong */void MYFunc(void);void myFunc();
/* OK */const char* my_func(void);my_struct_t* my_func(int32_t a, int32_t b);/* Wrong */const char *my_func(void);my_struct_t * my_func(void);
- 对齐所有的功能原型(使用相同/相似的功能)以提高可读性
/* OK, function names aligned */void set(int32_t a);my_type_t get(void);my_ptr_t* get_ptr(void);/* Wrong */void set(int32_t a);const char * get(void);
- 函数实现必须在单独的行中包含返回类型和可选的其他关键字
/* OK */int32_tfoo(void) { return 0;}/* OK */static const char*get_string(void) { return 'Hello world!\r\n';}/* Wrong */int32_t foo(void) { return 0;}
变量/* OK */int32_t a;int32_t my_var;int32_t myvar;/* Wrong */int32_t A;int32_t myVar;int32_t MYVar;
voidfoo(void) { int32_t a, b; /* OK */ char a; char b; /* Wrong, char type already exists */}
voidfoo(void) { int32_t a; a = bar(); int32_t b; /* Wrong, there is already executable statement */}
int32_t a, b;a = foo();if (a) { int32_t c, d; /* OK, c and d are in if-statement scope */ c = foo(); int32_t e; /* Wrong, there was already executable statement inside block */}
/* OK */char* a;/* Wrong */char *a;char * a;
- 当声明多个指针变量时，可以使用星号对变量名进行声明
/* OK */char *p, *n;
结构、枚举类型定义- 结构名或枚举名必须小写，单词之间有下划线_字符
- 结构或枚举可以包含typedef关键字
- 所有结构成员都必须小写
- 所有枚举成员必须是大写的
- 结构/枚举必须遵循doxygen文档语法
在声明结构体时，它可以使用以下三种不同的选项之一: 1、当结构体仅用名称声明时，它的名称后不能包含_t后缀。 struct struct_name { char* a; char b;};
2、当只使用typedef声明结构时，它的名称后面必须包含_t后缀。 typedef struct { char* a; char b;} struct_name_t;
3、当结构用name和typedef声明时，它不能包含t作为基本名称，它必须在它的名称后面包含t后缀作为typedef部分。 typedef struct struct_name { char* a; char b; char c;} struct_name_t;
错误声明的例子及其建议的纠正： /* a and b must be separated to 2 lines *//* Name of structure with typedef must include _t suffix */typedef struct { int32_t a, b;} a;/* Corrected version */typedef struct { int32_t a; int32_t b;} a_t;/* Wrong name, it must not include _t suffix */struct name_t { int32_t a; int32_t b;};/* Wrong parameters, must be all uppercase */typedef enum { MY_ENUM_TESTA, my_enum_testb,} my_enum_t;
/* OK */a_t a = { .a = 4, .b = 5,};/* Wrong */a_t a = {1, 2};
- 当为函数句柄引入new typedef时，使用_fn后缀
/* Function accepts 2 parameters and returns uint8_t *//* Name of typedef has `_fn` suffix */typedef uint8_t (*my_func_typedef_fn)(uint8_t p1, const char* p2);
复合语句- 每个复合语句必须包括左花括号和右花括号，即使它只包含1个嵌套语句
- 每个复合语句必须包含单个缩进;嵌套语句时，每个嵌套包含1个缩进大小
/* OK */if (c) { do_a();} else { do_b();}/* Wrong */if (c) do_a();else do_b();/* Wrong */if (c) do_a();else do_b();
- 在if或if-else-if语句的情况下，else必须与第一条语句的右括号在同一行
/* OK */if (a) {} else if (b) {} else {}/* Wrong */if (a) {}else {}/* Wrong */if (a) {}else{}
- 在do-while语句的情况下，while部分必须与do部分的右括号在同一行
/* OK */do { int32_t a; a = do_a(); do_b(a);} while (check());/* Wrong */do{/* ... */} while (check());/* Wrong */do {/* ... */}while (check());
if (a) { do_a();} else { do_b(); if (c) { do_c(); }}
- 不要做没有花括号的复合语句，即使是单个语句。下面的例子展示了一些不好的做法
if (a) do_b();else do_c();if (a) do_a(); else do_b();
- 空while循环、do-while循环或for循环必须包含花括号
/* OK */while (is_register_bit_set()) {}/* Wrong */while (is_register_bit_set());while (is_register_bit_set()) { }while (is_register_bit_set()) {}
- 如果while(或for、do-while等)为空(嵌入式编程中也可能是这种情况)，请使用空的单行括号
/* Wait for bit to be set in embedded hardware unituint32_t* addr = HW_PERIPH_REGISTER_ADDR;/* Wait bit 13 to be ready */while (*addr & (1 << 13)) {} /* OK, empty loop contains no spaces inside curly brackets */while (*addr & (1 << 13)) { } /* Wrong */while (*addr & (1 << 13)) { /* Wrong */}while (*addr & (1 << 13)); /* Wrong, curly brackets are missing. Can lead to compiler warnings or unintentional bugs */
/* Not recommended */int32_t a = 0;while (a < 10) { . .. ... ++a;}/* Better */for (size_t a = 0; a < 10; ++a) {}/* Better, if inc may not happen in every cycle */for (size_t a = 0; a < 10; ) { if (...) { ++a; }}
分支语句- 为每个case语句添加单个缩进
- 使用额外的单缩进break语句在每个case或default
/* OK, every case has single indent *//* OK, every break has additional indent */switch (check()) { case 0: do_a(); break; case 1: do_b(); break; default: break;}/* Wrong, case indent missing */switch (check()) {case 0: do_a(); break;case 1: do_b(); break;default: break;}/* Wrong */switch (check()) { case 0: do_a(); break; /* Wrong, break must have indent as it is under case */ case 1: do_b(); /* Wrong, indent under case is missing */ break; default: break;}
/* OK */switch (var) { case 0: do_job(); break; default: break;}/* Wrong, default is missing */switch (var) { case 0: do_job(); break;}
- 如果需要局部变量，则使用花括号并在里面放入break语句。将左花括号放在case语句的同一行
switch (a) { /* OK */ case 0: { int32_t a, b; char c; a = 5; /* ... */ break; } /* Wrong */ case 1: { int32_t a; break; } /* Wrong, break shall be inside */ case 2: { int32_t a; } break;}
宏和预处理指令- 总是使用宏而不是文字常量，特别是对于数字
- 所有的宏必须是全大写的，并带有下划线_字符(可选)，除非它们被明确标记为function，将来可能会被常规函数语法替换
/* OK */#define MY_MACRO(x) ((x) * (x))/* Wrong */#define square(x) ((x) * (x))
/* OK */#define MIN(x, y) ((x) < (y) ? (x) : (y))/* Wrong */#define MIN(x, y) x < y ? x : y
/* Wrong */#define MIN(x, y) (x) < (y) ? (x) : (y)#define SUM(x, y) (x) + (y)/* Imagine result of this equation using wrong SUM implementation */int32_t x = 5 * SUM(3, 4); /* Expected result is 5 * 7 = 35 */int32_t x = 5 * (3) + (4); /* It is evaluated to this, final result = 19 which is not what we expect *//* Correct implementation */#define MIN(x, y) ((x) < (y) ? (x) : (y))#define SUM(x, y) ((x) + (y))
- 当宏使用多个语句时，使用do-while(0)语句保护它
typedef struct { int32_t px, py;} point_t;point_t p; /* Define new point *//* Wrong implementation *//* Define macro to set point */#define SET_POINT(p, x, y) (p)->px = (x); (p)->py = (y) /* 2 statements. Last one should not implement semicolon */SET_POINT(&p, 3, 4); /* Set point to position 3, 4. This evaluates to... */(&p)->px = (3); (&p)->py = (4); /* ... to this. In this example this is not a problem. *//* Consider this ugly code, however it is valid by C standard (not recommended) */if (a) /* If a is true */ if (b) /* If b is true */ SET_POINT(&p, 3, 4);/* Set point to x = 3, y = 4 */ else SET_POINT(&p, 5, 6);/* Set point to x = 5, y = 6 *//* Evaluates to code below. Do you see the problem? */if (a) if (b) (&p)->px = (3); (&p)->py = (4); else (&p)->px = (5); (&p)->py = (6);/* Or if we rewrite it a little */if (a) if (b) (&p)->px = (3); (&p)->py = (4); else (&p)->px = (5); (&p)->py = (6);/* * Ask yourself a question: To which `if` statement `else` keyword belongs? * * Based on first part of code, answer is straight-forward. To inner `if` statement when we check `b` condition * Actual answer: Compilation error as `else` belongs nowhere *//* Better and correct implementation of macro */#define SET_POINT(p, x, y) do { (p)->px = (x); (p)->py = (y); } while (0) /* 2 statements. No semicolon after while loop *//* Or even better */#define SET_POINT(p, x, y) do { \ /* Backslash indicates statement continues in new line */ (p)->px = (x); \ (p)->py = (y); \} while (0) /* 2 statements. No semicolon after while loop *//* Now original code evaluates to */if (a) if (b) do { (&p)->px = (3); (&p)->py = (4); } while (0); else do { (&p)->px = (5); (&p)->py = (6); } while (0);/* Every part of `if` or `else` contains only `1` inner statement (do-while), hence this is valid evaluation *//* To make code perfect, use brackets for every if-ifelse-else statements */if (a) { /* If a is true */ if (b) { /* If b is true */ SET_POINT(&p, 3, 4);/* Set point to x = 3, y = 4 */ } else { SET_POINT(&p, 5, 6);/* Set point to x = 5, y = 6 */ }}
/* OK */#if defined(XYZ)#if defined(ABC)/* do when ABC defined */#endif /* defined(ABC) */#else /* defined(XYZ) *//* Do when XYZ not defined */#endif /* !defined(XYZ) *//* Wrong */#if defined(XYZ) #if defined(ABC) /* do when ABC defined */ #endif /* defined(ABC) */#else /* defined(XYZ) */ /* Do when XYZ not defined */#endif /* !defined(XYZ) */
文档文档化的代码允许doxygen解析和通用的html/pdf/latex输出，因此正确地执行是非常重要的。 - 对变量、函数和结构/枚举使用doxygen支持的文档样式
- 经常使用\作为doxygen，不要使用@
- 始终使用5x4空格(5个制表符)作为文本行开始的偏移量
/** * \brief Holds pointer to first entry in linked list * Beginning of this text is 5 tabs (20 spaces) from beginning of line */statictype_t* list;
- 每个结构/枚举成员都必须包含文档
- 注释的开头使用12x4空格偏移量
/** * \brief This is point struct * \note This structure is used to calculate all point * related stuff */typedef struct { int32_t x; /*!< Point X coordinate */ int32_t y; /*!< Point Y coordinate */ int32_t size; /*!< Point size. Since comment is very big, you may go to next line */} point_t;/** * \brief Point color enumeration */typedef enum { COLOR_RED, /*!< Red color. This comment has 12x4 spaces offset from beginning of line */ COLOR_GREEN, /*!< Green color */ COLOR_BLUE, /*!< Blue color */} point_color_t;
- 函数的文档必须在函数实现中编写(通常是源文件)
- 函数必须包括简要和所有参数文档
- 如果每个参数分别为in或out输入和输出，则必须注意
- 如果函数返回某个值，则必须包含返回形参。这不适用于void函数
- 函数可以包含其他doxygen关键字，如note或warning
- 在参数名和描述之间使用冒号:
/** * \brief Sum `2` numbers * \param[in] a: First number * \param[in] b: Second number * \return Sum of input values */int32_tsum(int32_t a, int32_t b) { return a + b;}/** * \brief Sum `2` numbers and write it to pointer * \note This function does not return value, it stores it to pointer instead * \param[in] a: First number * \param[in] b: Second number * \param[out] result: Output variable used to save result */voidvoid_sum(int32_t a, int32_t b, int32_t* result) { *result = a + b;}
- 如果函数返回枚举的成员，则使用ref关键字指定哪个成员
/** * \brief My enumeration */typedef enum { MY_ERR, /*!< Error value */ MY_OK /*!< OK value */} my_enum_t;/** * \brief Check some value * \return \ref MY_OK on success, member of \ref my_enum_t otherwise */my_enum_tcheck_value(void) { return MY_OK;}
- 对常量或数字使用符号(' NULL ' => NULL)
/** * \brief Get data from input array * \param[in] in: Input data * \return Pointer to output data on success, `NULL` otherwise */const void *get_data(const void* in) { return in;}
- 宏的文档必须包括hideinitializer doxygen命令
/** * \brief Get minimal value between `x` and `y` * \param[in] x: First value * \param[in] y: Second value * \return Minimal value between `x` and `y` * \hideinitializer */#define MIN(x, y) ((x) < (y) ? (x) : (y))
头/源文件- 在文件末尾留下一个空行
- 每个文件都必须包括文件的doxygen注释和后跟空行的简要描述(使用doxygen时)
/** * \file template.h * \brief Template include file */ /* Here is empty line */
- 每个文件(头文件或源文件)必须包含许可证(开始注释包括单个星号，因为doxygen必须忽略这个)
- 使用与项目/库已经使用的相同的许可证
/** * \file template.h * \brief Template include file *//* * Copyright (c) year FirstName LASTNAME * * Permission is hereby granted, free of charge, to any person * obtaining a copy of this software and associated documentation * files (the 'Software'), to deal in the Software without restriction, * including without limitation the rights to use, copy, modify, merge, * publish, distribute, sublicense, and/or sell copies of the Software, * and to permit persons to whom the Software is furnished to do so, * subject to the following conditions: * * The above copyright notice and this permission notice shall be * included in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE * AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR * OTHER DEALINGS IN THE SOFTWARE. * * This file is part of library_name. * * Author: FirstName LASTNAME <optional_email@example.com> */
- 头文件必须包含保护符#ifndef
- 头文件必须包含c++检查
- 在c++检查之外包含外部头文件
- 首先用STL C文件包含外部头文件，然后是应用程序自定义文件
- 头文件必须包含其他所有头文件，以便正确编译，但不能包含更多头文件(如果需要，.c应该包含其余的头文件)
- 头文件必须只公开模块公共变量/类型/函数
- 在头文件中使用extern作为全局模块变量，稍后在源文件中定义它们
/* file.h ... */#ifndef ...extern int32_t my_variable; /* This is global variable declaration in header */#endif/* file.c ... */int32_t my_variable; /* Actually defined in source */
- 不要把.c文件包含在另一个.c文件中
- .c文件应该首先包含相应的.h文件，然后是其他文件，除非另有明确的必要
- 在头文件中不包含模块私有声明
- 头文件示例(示例中没有license)
/* License comes here */#ifndef TEMPLATE_HDR_H#define TEMPLATE_HDR_H/* Include headers */#ifdef __cplusplusextern 'C' {#endif /* __cplusplus *//* File content here */#ifdef __cplusplus}#endif /* __cplusplus */#endif /* TEMPLATE_HDR_H */
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