subsurface/CODINGSTYLE.md

Coding Style

Here are some of the basics that we are trying to enforce for our coding style and conventions. The existing code (as of the commit that adds these lines) is not yet fully consistent to these rules, but following these rules will make sure that no one yells at you about your patches.

We have a script that can be used to reformat code to be reasonably close to these rules; it's in scripts/whitespace.pl - this script requires clang-format to be installed (which sadly isn't installed by default on any of our platforms; even on Mac where clang is the default compiler).

At the end of this file are some ideas for your .emacs file (if that's your editor of choice) as well as for QtCreator. If you have settings for other editors that implement this coding style, please add them here.

Basic rules

• all indentation is tabs (set to 8 char) with the exception of continuation lines that are aligned with tabs and then spaces

• all keywords followed by a '(' have a space in between

    if (condition)
  
    for (i = 0; i < 5; i++)
  

• function calls do NOT have a space between their name and argument

    i = some_function(argument);
  

• usually there is no space on the inside of parenthesis (see examples above)

• function / method implementations have their opening curly braces in column 1

• all other opening curly braces follow at the end of the line, with a space separating them:

    if (condition) {
    	dosomething();
    	dosomethingelse();
    }
  

• both sides of an if / else clause either use or do not use curly braces:

    if (condition)
    	i = 4;
    else
    	j = 6;
  
    if (condition) {
    	i = 6;
    } else {
    	i = 4;
    	j = 6;
    }
  

• use space to make visual separation easier

    a = b + 3 + e / 4;
  

• continuation lines have the operator / comma at the end

    if (very_long_condition_1 ||
        condition_2)
  
    b = a + (c + d +
    	 f + z);
  

• in a C++ constructor initialization list, the colon is on the same line and continuation lines are aligned as the rule above:

    ClassName::ClassName() : x(1),
    	y(2),
    	z(3)
    {
    }
  

• unfortunate inconsistency

  • C code usually uses underscores to structure names

    variable_in_C
  

  • In contrast, C++ code usually uses camelCase

    variableInCPlusPlus
  

  where the two meet, use your best judgment and go for best consistency (i.e., where does the variable "originate")

• there is a strong preference for lower case file names; sometimes conventions or outside requirements make camelCase filenames the better (or only) choice, but absent such an outside reason all file names should be lower case

• cpp/h file names should usually be identical to the class name but in lower case. Where it seems appropriate, multiple, closely related classes can be in a single file with a more generic name.

• switch statements with blocks are a little bit special (to avoid indenting too far)

    switch (foo) {
    case FIRST:
    	whatever();
    	break;
    case SECOND: {
    	int i;
    	for (i = 0; i < 5; i++)
    		do_something(i);
    }
    }
  

Coding conventions

• variable declarations In C code we really like them to be at the beginning of a code block, not interspersed in the middle. in C++ we are a bit less strict about this - but still, try not to go crazy. Notably, in C++ the lifetime of a variable often coincides with the lifetime of a resource (e.g. file) and therefore the variable is defined at the place where the resource is needed.

• The *, & and && declarators are grouped with the name, not the type (classical C-style) as in char *string instead of char* string. This reflects the precedence rules of the language: int &i means that the name i stands for a reference [to an object with type int], not that i stands for an object of the type [reference to int]. Although this may seem like hairsplitting (both interpretations have the same effect) it is crucial in the definition of multiple variables, such as

  struct dive *next, **pprev;
  

• In C++ code, we generally use explicit types in variable declarations for clarity. Use auto sparingly and only in cases where code readability improves. Two classical examples are:

  • Iterators, whose type names often are verbose:

    auto it = m_trackers.find(when);
    

    is not only distinctly shorter than

    QMap<qint64, gpsTracker>::iterator it = m_trackers.find(when);
    

    it will also continue working if a different data structure is chosen.
  • If the type is given in the same line anyway. Thus,

    auto service = qobject_cast<QLowEnergyService*>(sender());
    

    is easier to read than and conveys the same information as

    QLowEnergyService *service = qobject_cast<QLowEnergyService*>(sender());
    

  • If the variable is a container that is only assigned to a local variable to be able to use it in a range-based for loop

    const auto l = device.serviceUuids();
    for (QBluetoothUuid id: serviceUuids) {
    

    The variable has also to be const to avoid that Qt containers will do a deep copy when the range bases for loop will call the begin() method internally.

• text strings The default language of subsurface is US English so please use US English spelling and terminology. User-visible strings should be passed to the tr() function to enable translation into other languages.

  • like this

    QString msgTitle = tr("Submit user survey.");
    

  • rather than

    QString msgTitle = "Submit user survey.";
    

  This works by default in classes (indirectly) derived from QObject. Each string to be translated is associated with a context, which corresponds to the class name. Classes that are not derived from QObject can generate the tr() functions by using the Q_DECLARE_TR_FUNCTIONS macro:

    #include <QCoreApplication>
  
    class myClass {
    	Q_DECLARE_TR_FUNCTIONS(gettextfromC)
    	...
    };
  

  As an alternative, which also works outside of class context, the tr() function of a different class can be called. This avoids creating multiple translations for the same string:

    gettextFromC::tr("%1km")
  

  The gettextFromC class in the above example was created as a catch-all context for translations accessed in C code. But it can also be used from C++ helper functions. To use it from C, include the "core/gettext.h" header and invoke the translate() macro:

    #include "core/gettext.h"
  
    report_error(translate("gettextFromC", "Remote storage and local data diverged"));
  

  It is crucial to pass "gettextFromC" as a first macro argument so that Qt is able to associate the string with the correct context. The translate macro returns a cached C-style string, which is generated at runtime when the particular translation string is encountered for the first time. It remains valid during the whole application's life time.

  Outside of function context, the QT_TRANSLATE_NOOP macro can be used as in

  struct ws_info_t ws_info[100] = {
    { QT_TRANSLATE_NOOP("gettextFromC", "integrated"), 0 },
    { QT_TRANSLATE_NOOP("gettextFromC", "belt"), 0 },
    { QT_TRANSLATE_NOOP("gettextFromC", "ankle"), 0 },
    { QT_TRANSLATE_NOOP("gettextFromC", "backplate"), 0 },
    { QT_TRANSLATE_NOOP("gettextFromC", "clip-on"), 0 },
  };
  

  Note that here, the texts will be scheduled for translation with the "gettextFromC" context, but the array is only initialized with the original text. The actual translation has to be performed later in code. For C-code, the QT_TRANSLATE_NOOP macro is defined in the "core/gettext.h" header.

• UI text style These guidelines are designed to ensure consistency in presentation within Subsurface. Only the first word of multi-word text strings should be capitalized unless a word would normally be capitalized mid-sentence, like Africa. This applies to all UI text including menus, menu items, tool-tips, button text and label text etc. e.g. "Check for updates" rather than "Check for Updates". We also capitalize Subsurface (NOTE: not SubSurface) when referring to the application itself. Abbreviations should end with a period, e.g. "temp." not "temp" for temperature Numerals in chemical formulae should use subscript characters e.g. O₂ not O2 Partial pressures in Subsurface are, by convention, abbreviated with a single "p" rather than 2, as in pO₂ not ppO₂ Where more than one term exists for something, please choose the one already in use within Subsurface e.g. Cylinder vs. Tank.

• string manipulation

• user interface In UI part of the code use of QString methods is preferred, see this pretty good guide in QString documentation

• core components In the core part of the code, C-string should be used. C-string manipulation is not always straightforward specifically when it comes to memory allocation, a set of helper functions has been developed to help with this. Documentation and usage examples can be found in core/membuffer.h

Sample Settings

Emacs

These lines in your .emacs file should get you fairly close when it comes to indentation - many of the other rules you have to follow manually

;; indentation
(defun c-lineup-arglist-tabs-only (ignored)
  "Line up argument lists by tabs, not spaces"
  (let* ((anchor (c-langelem-pos c-syntactic-element))
         (column (c-langelem-2nd-pos c-syntactic-element))
         (offset (- (1+ column) anchor))
         (steps (floor offset c-basic-offset)))
    (* (max steps 1)
       c-basic-offset)))

(add-hook 'c-mode-common-hook
          (lambda ()
            ;; Add kernel style
            (c-add-style
             "linux-tabs-only"
             '("linux" (c-offsets-alist
                        (arglist-cont-nonempty
                         c-lineup-gcc-asm-reg
                         c-lineup-arglist-tabs-only))))))

(add-hook 'c-mode-hook
          (lambda ()
            (let ((filename (buffer-file-name)))
              ;; Enable kernel mode for the appropriate files
                (setq indent-tabs-mode t)
                (c-set-style "linux-tabs-only"))))

(add-hook 'c++-mode-hook
          (lambda ()
            (let ((filename (buffer-file-name)))
              ;; Enable kernel mode for the appropriate files
                (setq indent-tabs-mode t)
                (c-set-style "linux-tabs-only"))))

QtCreator

These settings seem to get indentation right in QtCreator. Making TAB always adjust indent makes it hard to add hard tabs before '' when creating continuing lines. Copying a tab with your mouse / ctrl-C and inserting it with ctrl-V seems to work around that problem (use Command instead of ctrl on your Mac) Save this XML code below to a file, open Preferences (or Tools->Options) in QtCreator, pick C++ in the left column and then click on Import... to open the file you just created. Now you should have a "Subsurface" style that you can select which should work well for our coding style.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE QtCreatorCodeStyle>
<!-- Written by QtCreator 3.0.0, 2014-02-27T07:52:57. -->
<qtcreator>
 <data>
  <variable>CodeStyleData</variable>
  <valuemap type="QVariantMap">
   <value type="bool" key="AlignAssignments">false</value>
   <value type="bool" key="AutoSpacesForTabs">false</value>
   <value type="bool" key="BindStarToIdentifier">true</value>
   <value type="bool" key="BindStarToLeftSpecifier">false</value>
   <value type="bool" key="BindStarToRightSpecifier">false</value>
   <value type="bool" key="BindStarToTypeName">false</value>
   <value type="bool" key="ExtraPaddingForConditionsIfConfusingAlign">false</value>
   <value type="bool" key="IndentAccessSpecifiers">false</value>
   <value type="bool" key="IndentBlockBody">true</value>
   <value type="bool" key="IndentBlockBraces">false</value>
   <value type="bool" key="IndentBlocksRelativeToSwitchLabels">false</value>
   <value type="bool" key="IndentClassBraces">false</value>
   <value type="bool" key="IndentControlFlowRelativeToSwitchLabels">true</value>
   <value type="bool" key="IndentDeclarationsRelativeToAccessSpecifiers">true</value>
   <value type="bool" key="IndentEnumBraces">false</value>
   <value type="bool" key="IndentFunctionBody">true</value>
   <value type="bool" key="IndentFunctionBraces">false</value>
   <value type="bool" key="IndentNamespaceBody">false</value>
   <value type="bool" key="IndentNamespaceBraces">false</value>
   <value type="int" key="IndentSize">8</value>
   <value type="bool" key="IndentStatementsRelativeToSwitchLabels">true</value>
   <value type="bool" key="IndentSwitchLabels">false</value>
   <value type="int" key="PaddingMode">2</value>
   <value type="bool" key="SpacesForTabs">false</value>
   <value type="int" key="TabSize">8</value>
  </valuemap>
 </data>
 <data>
  <variable>DisplayName</variable>
  <value type="QString">Subsurface</value>
 </data>
</qtcreator>

Vim

As everybody knows vim is a way better editor than emacs and thus needs to be in this file too. Put this into your .vimrc and this should produce something close to our coding standards.

" Subsurface coding style
filetype plugin indent on
filetype detect
set cindent tabstop=8 shiftwidth=8 cinoptions=l1,:0,(0,g0
" TODO: extern "C" gets indented

" And some sane defaults, optional, but quite nice
set nocompatible
syntax on
colorscheme default
set hls
set is

" The default blue is just impossible to see on a black terminal
highlight Comment ctermfg=Brown

" clearly point out when someone have trailing spaces
highlight ExtraWhitespace ctermbg=red guibg=red

" Show trailing whitespace and spaces before a tab:
match ExtraWhitespace /\s\+$\| \+\ze\t/