Guidelines for API documentation » History » Version 4
neels, 06/20/2017 02:11 AM
1 | 1 | neels | h1. Guidelines for API documentation |
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3 | We use doxygen for API documentation, following these guidelines: |
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5 | Use the @/*!@ (Qt-style) doxygen markers. |
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6 | |||
7 | Since we are using the AUTOBRIEF feature, always end the first sentence with a full-stop "." to mark the end of the short description. |
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8 | This allows omitting the @\brief@ markers everywhere. |
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9 | |||
10 | Never rely on line breaks as semantic separation or to end a sentence, always use proper punctuation. The API doc may be rendered with different line breaks than in the source file. |
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11 | |||
12 | 4 | neels | h2. Locations |
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14 | Header files usually contain merely function declarations bare of any API docs. The API doc comment should be in a @.c@ file at the definition of a function. |
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16 | Structs and enums defined in a header file, though, also have their API doc comments in that @.h@ file. |
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17 | |||
18 | h2. Grammar |
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20 | Always use the imperative form, i.e. omit wording like "This function does", and avoid writing documentation that merely mirrors a function's name. For example: |
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21 | |||
22 | <pre> |
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23 | /*! Return a (static) buffer containing a hexdump of the msg. |
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24 | * \param[in] msg message buffer |
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25 | * \returns a pointer to a static char array |
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26 | */ |
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27 | const char *msgb_hexdump(const struct msgb *msg) |
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28 | { |
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29 | ... |
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30 | </pre> |
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31 | |||
32 | |||
33 | h2. Parameters |
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34 | |||
35 | All parameters of a function should be documented. Input params are documented with @\param[in]@, where out-parameters (pointers to which returned data is written) are documented with @\param[out]@. Rarely, a param is both: @\param[inout]@. |
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36 | |||
37 | <pre> |
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38 | /*! Apply nifty algorithm. |
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39 | * \param[in] x0 First factor. |
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40 | * \param[in] n Amount of values to calculate. |
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41 | * \param[out] buf Write calculated values to this buffer. |
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42 | * |
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43 | * Optional longer function description. */ |
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44 | </pre> |
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45 | |||
46 | 1 | neels | h2. File comments |
47 | |||
48 | If a file contains a descriptive comment, this comment should be right at the start of the file, as a doxygen @\file@ section. |
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49 | The first sentence must be ended by a full stop "." to mark the end of the short description. |
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50 | The copyright notice shall not be part of such API doc file comment. |
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51 | |||
52 | <pre> |
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53 | /*! \file foo.c |
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54 | * Short description. */ |
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55 | /* |
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56 | * (C) 2017 ... Copyright not in a doxygen comment |
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57 | * license information |
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58 | */ |
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59 | </pre> |
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60 | |||
61 | or |
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62 | |||
63 | <pre> |
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64 | /*! \file foo.c |
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65 | * Short description. |
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66 | * |
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67 | * More information in multiple lines. |
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68 | */ |
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69 | /* |
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70 | * (C) 2017 ... |
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71 | */ |
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72 | </pre> |
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73 | |||
74 | h2. Groups |
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75 | |||
76 | Doxygen allows grouping elements: a group can include code elements and also entire files. |
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77 | |||
78 | This works by enclosing the items to be grouped between an opening and a closing marker: |
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79 | |||
80 | * A @\defgroup@ initially defines a group, this shall exist only once. |
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81 | * More items can be added using an @\addtogroup@ marker. |
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82 | * Both have to be closed by "@}". |
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83 | |||
84 | For example: |
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85 | |||
86 | <pre> |
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87 | /*! \defgroup groupname Short description of the group. |
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88 | * @{ |
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89 | */ |
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90 | |||
91 | struct type_that_belongs_to_group { |
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92 | ... |
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93 | }; |
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94 | |||
95 | void func_that_belongs_to_group() |
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96 | { |
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97 | ... |
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98 | } |
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99 | |||
100 | /*! @} */ |
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101 | </pre> |
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102 | |||
103 | and |
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104 | |||
105 | <pre> |
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106 | /*! \addtogroup groupname |
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107 | * @{ |
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108 | */ |
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109 | |||
110 | 3 | neels | ... |
111 | 1 | neels | |
112 | /*! @} */ |
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113 | </pre> |
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114 | |||
115 | If a *file* should be added to a group, add a (possibly) second, short descriptionless @\file@ tag to the group start. To clearly mark that the purpose is to add to the group, do so within the same comment block: |
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116 | |||
117 | <pre> |
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118 | /*! \file foo.c |
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119 | 2 | neels | * File's description. */ |
120 | 1 | neels | /* |
121 | * (C) ... |
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122 | */ |
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123 | |||
124 | /*! \addtogroup groupname |
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125 | * @{ |
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126 | * \file foo.c */ |
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127 | |||
128 | ... |
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129 | |||
130 | /*! @} */ |
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131 | </pre> |
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132 | |||
133 | The point is that we like to have a file's short description near the start of the file, to also serve us well when we're reading only the .h file. But to be included in a group, the doxygen group start must precede the @\file@ tag. Also, the doxygen group should rather not enclose @#include@ directives, to clearly exclude those from the group. Hence, the best way is to keep the file's actual description at the top of the file, and add a second descriptionless @\file@ with the group opening. |
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135 | A group may contain a short as well as a longer description. We often @\defgroup@ in a @.h@ file but keep the longer description in an @\addtogroup@ in a @.c@ file. Any @\file@ tags must follow *after* such description, or the description will be associated with the file instead of the group: |
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136 | |||
137 | @.h@ file: |
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138 | <pre> |
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139 | /*! \defgroup groupname Short description of the group. |
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140 | * @{ |
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141 | */ |
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142 | |||
143 | ... |
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144 | |||
145 | /*! @} */ |
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146 | </pre> |
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147 | |||
148 | @.c file: |
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149 | |||
150 | <pre> |
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151 | /*! \addtogroup groupname |
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152 | * @{ |
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153 | * Longer description of the group. |
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154 | * - contains a |
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155 | * - bullet list |
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156 | * |
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157 | * As well as a |
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158 | * |
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159 | * Code example |
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160 | * block |
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161 | * |
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162 | * All of which must not be below the directive adding this file to the group: |
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163 | * |
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164 | * \file foo.c */ |
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165 | |||
166 | [...] |
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167 | |||
168 | /*! @} */ |
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169 | </pre> |
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170 | |||
171 | Often, a file's description matches or is identical with a group's description. In that case, the file's description header comment can be omitted to avoid duplicating identical descriptions. |
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172 | |||
173 | <pre> |
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174 | /* |
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175 | * (C) 2017 ... |
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176 | */ |
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177 | |||
178 | /* \addtogroup group |
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179 | * @{ |
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180 | * Description... |
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181 | * |
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182 | * \file foo.c */ |
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183 | |||
184 | ... |
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185 | |||
186 | /* @} */ |
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187 | </pre> |