Guidelines for API documentation » History » Version 9
neels, 06/20/2017 02:49 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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19 | |||
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 | h2. Parameters |
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33 | |||
34 | 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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35 | |||
36 | <pre> |
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37 | /*! Apply nifty algorithm. |
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38 | * \param[in] x0 First factor. |
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39 | * \param[in] n Amount of values to calculate. |
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40 | * \param[out] buf Write calculated values to this buffer. |
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41 | * |
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42 | * Optional longer function description. */ |
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43 | 1 | neels | </pre> |
44 | 7 | neels | |
45 | 8 | neels | It is also possible to document parameters without a direction, using merely @\param param_name Description@, however, it is desirable to always indicate @[in]@, @[out]@ or @[inout]@. |
46 | 4 | neels | |
47 | 1 | neels | h2. File comments |
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49 | 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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50 | The first sentence must be ended by a full stop "." to mark the end of the short description. |
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51 | The copyright notice shall not be part of such API doc file comment. |
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52 | |||
53 | <pre> |
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54 | /*! \file foo.c |
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55 | * Short description. */ |
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56 | /* |
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57 | * (C) 2017 ... Copyright not in a doxygen comment |
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58 | * license information |
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59 | */ |
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60 | </pre> |
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61 | |||
62 | or |
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63 | |||
64 | <pre> |
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65 | /*! \file foo.c |
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66 | * Short description. |
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67 | * |
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68 | * More information in multiple lines. |
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69 | */ |
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70 | /* |
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71 | * (C) 2017 ... |
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72 | */ |
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73 | </pre> |
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74 | |||
75 | 9 | neels | If a file needs no description, it is ok to omit the @\file@ tag entirely. Since we are using the EXTRACT_ALL = YES, files lacking a @\file@ tag are still listed in the API docs. |
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77 | 1 | neels | h2. Groups |
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79 | Doxygen allows grouping elements: a group can include code elements and also entire files. |
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80 | |||
81 | This works by enclosing the items to be grouped between an opening and a closing marker: |
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82 | |||
83 | * A @\defgroup@ initially defines a group, this shall exist only once. |
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84 | * More items can be added using an @\addtogroup@ marker. |
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85 | * Both have to be closed by "@}". |
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86 | |||
87 | For example: |
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88 | |||
89 | <pre> |
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90 | /*! \defgroup groupname Short description of the group. |
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91 | * @{ |
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92 | */ |
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93 | |||
94 | struct type_that_belongs_to_group { |
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95 | ... |
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96 | }; |
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97 | |||
98 | void func_that_belongs_to_group() |
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99 | { |
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100 | ... |
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101 | } |
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102 | |||
103 | /*! @} */ |
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104 | </pre> |
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105 | |||
106 | and |
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107 | |||
108 | <pre> |
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109 | /*! \addtogroup groupname |
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110 | * @{ |
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111 | */ |
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112 | |||
113 | 3 | neels | ... |
114 | 1 | neels | |
115 | /*! @} */ |
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116 | </pre> |
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117 | |||
118 | 5 | neels | 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: |
119 | 1 | neels | |
120 | <pre> |
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121 | /*! \file foo.c |
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122 | 2 | neels | * File's description. */ |
123 | 1 | neels | /* |
124 | * (C) ... |
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125 | */ |
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126 | |||
127 | /*! \addtogroup groupname |
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128 | * @{ |
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129 | * \file foo.c */ |
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130 | |||
131 | ... |
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132 | |||
133 | /*! @} */ |
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134 | </pre> |
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135 | |||
136 | 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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138 | 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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139 | |||
140 | @.h@ file: |
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141 | <pre> |
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142 | /*! \defgroup groupname Short description of the group. |
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143 | * @{ |
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144 | */ |
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145 | |||
146 | ... |
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147 | |||
148 | /*! @} */ |
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149 | </pre> |
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150 | |||
151 | @.c file: |
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152 | |||
153 | <pre> |
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154 | /*! \addtogroup groupname |
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155 | * @{ |
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156 | * Longer description of the group. |
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157 | * - contains a |
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158 | * - bullet list |
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159 | * |
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160 | * As well as a |
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161 | * |
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162 | * Code example |
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163 | * block |
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164 | * |
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165 | 6 | neels | * All of which must not be below the directive adding this file to the group... |
166 | 1 | neels | * |
167 | * \file foo.c */ |
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168 | |||
169 | [...] |
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170 | |||
171 | /*! @} */ |
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172 | </pre> |
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173 | |||
174 | 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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175 | |||
176 | <pre> |
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177 | /* |
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178 | * (C) 2017 ... |
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179 | */ |
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180 | |||
181 | /* \addtogroup group |
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182 | * @{ |
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183 | * Description... |
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184 | * |
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185 | * \file foo.c */ |
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186 | |||
187 | ... |
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188 | |||
189 | /* @} */ |
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190 | </pre> |