Guidelines for API documentation » History » Version 12
neels, 10/23/2017 10:38 PM
1 | 1 | neels | h1. Guidelines for API documentation |
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3 | 12 | neels | Find the current API doc in HTML form here: http://ftp.osmocom.org/api/latest/ |
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5 | 1 | neels | We use doxygen for API documentation, following these guidelines: |
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7 | Use the @/*!@ (Qt-style) doxygen markers. |
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9 | 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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10 | This allows omitting the @\brief@ markers everywhere. |
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12 | 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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14 | 4 | neels | h2. Locations |
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16 | 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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18 | Structs and enums defined in a header file, though, also have their API doc comments in that @.h@ file. |
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20 | 10 | neels | Comments for single-line items like enum values or struct members can be placed on the same line using @/*!< Description */@. |
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22 | 4 | neels | h2. Grammar |
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24 | 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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25 | |||
26 | <pre> |
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27 | /*! Return a (static) buffer containing a hexdump of the msg. |
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28 | * \param[in] msg message buffer |
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29 | * \returns a pointer to a static char array |
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30 | */ |
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31 | const char *msgb_hexdump(const struct msgb *msg) |
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32 | { |
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33 | ... |
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34 | </pre> |
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35 | |||
36 | h2. Parameters |
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37 | 1 | neels | |
38 | 12 | neels | 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[in,out]@. |
39 | 4 | neels | |
40 | <pre> |
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41 | /*! Apply nifty algorithm. |
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42 | * \param[in] x0 First factor. |
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43 | * \param[in] n Amount of values to calculate. |
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44 | * \param[out] buf Write calculated values to this buffer. |
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45 | * |
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46 | * Optional longer function description. */ |
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47 | 1 | neels | </pre> |
48 | 7 | neels | |
49 | 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]@. |
50 | 4 | neels | |
51 | 1 | neels | h2. File comments |
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53 | 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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54 | The first sentence must be ended by a full stop "." to mark the end of the short description. |
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55 | The copyright notice shall not be part of such API doc file comment. |
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56 | |||
57 | <pre> |
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58 | /*! \file foo.c |
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59 | * Short description. */ |
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60 | /* |
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61 | * (C) 2017 ... Copyright not in a doxygen comment |
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62 | * license information |
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63 | */ |
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64 | </pre> |
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65 | |||
66 | or |
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67 | |||
68 | <pre> |
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69 | /*! \file foo.c |
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70 | * Short description. |
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71 | * |
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72 | * More information in multiple lines. |
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73 | */ |
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74 | /* |
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75 | * (C) 2017 ... |
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76 | */ |
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77 | </pre> |
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79 | 11 | neels | If a file needs no description, it is ok to omit the @\file@ tag entirely. Since we are using EXTRACT_ALL = YES, files lacking a @\file@ tag are still listed in the API docs. |
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81 | 1 | neels | h2. Groups |
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83 | Doxygen allows grouping elements: a group can include code elements and also entire files. |
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85 | This works by enclosing the items to be grouped between an opening and a closing marker: |
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87 | * A @\defgroup@ initially defines a group, this shall exist only once. |
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88 | * More items can be added using an @\addtogroup@ marker. |
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89 | * Both have to be closed by "@}". |
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90 | |||
91 | For example: |
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92 | |||
93 | <pre> |
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94 | /*! \defgroup groupname Short description of the group. |
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95 | * @{ |
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96 | */ |
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97 | |||
98 | struct type_that_belongs_to_group { |
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99 | ... |
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100 | }; |
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101 | |||
102 | void func_that_belongs_to_group() |
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103 | { |
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104 | ... |
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105 | } |
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106 | |||
107 | /*! @} */ |
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108 | </pre> |
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109 | |||
110 | and |
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111 | |||
112 | <pre> |
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113 | /*! \addtogroup groupname |
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114 | * @{ |
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115 | */ |
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116 | |||
117 | 3 | neels | ... |
118 | 1 | neels | |
119 | /*! @} */ |
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120 | </pre> |
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122 | 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: |
123 | 1 | neels | |
124 | <pre> |
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125 | /*! \file foo.c |
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126 | 2 | neels | * File's description. */ |
127 | 1 | neels | /* |
128 | * (C) ... |
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129 | */ |
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130 | |||
131 | /*! \addtogroup groupname |
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132 | * @{ |
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133 | * \file foo.c */ |
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134 | |||
135 | ... |
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136 | |||
137 | /*! @} */ |
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138 | </pre> |
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140 | 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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142 | 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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144 | @.h@ file: |
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145 | <pre> |
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146 | /*! \defgroup groupname Short description of the group. |
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147 | * @{ |
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148 | */ |
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149 | |||
150 | ... |
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151 | |||
152 | /*! @} */ |
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153 | </pre> |
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154 | |||
155 | @.c file: |
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156 | |||
157 | <pre> |
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158 | /*! \addtogroup groupname |
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159 | * @{ |
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160 | * Longer description of the group. |
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161 | * - contains a |
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162 | * - bullet list |
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163 | * |
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164 | * As well as a |
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165 | * |
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166 | * Code example |
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167 | * block |
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168 | * |
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169 | 6 | neels | * All of which must not be below the directive adding this file to the group... |
170 | 1 | neels | * |
171 | * \file foo.c */ |
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172 | |||
173 | [...] |
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174 | |||
175 | /*! @} */ |
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176 | </pre> |
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177 | |||
178 | 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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179 | |||
180 | <pre> |
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181 | /* |
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182 | * (C) 2017 ... |
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183 | */ |
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184 | |||
185 | /* \addtogroup group |
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186 | * @{ |
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187 | * Description... |
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188 | * |
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189 | * \file foo.c */ |
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190 | |||
191 | ... |
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192 | |||
193 | /* @} */ |
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194 | </pre> |