Latest revision |
Your text |
Line 7: |
Line 7: |
|
| |
|
| == Formatting == | | == Formatting == |
|
| |
| === Line Length ===
| |
|
| |
| There is no fixed line length. In general, strive for clarity and readability and use your own judgement.
| |
|
| |
| Everyone has access to monitors with more than 80 columns, but even so, exceptionally long lines can be hard to read. However, keeping code together on a line that is logically one unit does improve readability.
| |
|
| |
|
| === Indentation === | | === Indentation === |
|
| |
|
| * Use only spaces, with 2 spaces per indent.
| | Use only spaces, and indent 2 spaces at a time. |
| * Tabs are prohibited.
| |
| | |
| ==== Functions, class, struct, enum ====
| |
| | |
| The curly braces defining the beginning and end of the block should appear on their own line.
| |
| | |
| The braces should not be indented, i.e., they align at the same indentation level as the keyword such as {{codeline|class}}.
| |
| | |
| The body of the block is indented.
| |
|
| |
|
| Note that class access specifiers {{codeline|public}}, {{codeline|protected}}, {{codeline|private}} are not indented.
| | We use spaces for indentation. Absolutely do not use tabs in your code. |
| | You should probably set your editor to emit spaces when you hit the tab key. |
|
| |
|
| Example:
| | When indenting, indent the statement after control |
| | | structures (like {{codeline|if}}, {{codeline|while}}, etc.). If there |
| <syntaxhighlight lang="cpp">
| | is a compound statement, indent ''both'' the curly braces and the |
| class MatrixType
| | body of the statement (so that the body gets indented by ''two'' |
| {
| | indents). This format is known as "GNU style" and is an option for |
| public:
| | some code formatting tools. Example indenting: |
| enum matrix_type
| |
| {
| |
| Unknown = 0,
| |
| Full,
| |
| Rectangular
| |
| };
| |
| | |
| }
| |
| </syntaxhighlight>
| |
| | |
| ==== Control structures (if, while, ...) ====
| |
| | |
| When indenting, indent the statement after control structures (like {{codeline|if}}, {{codeline|while}}, etc.). | |
| | |
| If there is a compound statement, indent ''both'' the curly braces and the body of the statement (so that the body gets indented by ''two'' indents). | |
| | |
| Example: | |
|
| |
|
| <syntaxhighlight lang="cpp"> | | <syntaxhighlight lang="cpp"> |
Line 63: |
Line 32: |
| </syntaxhighlight> | | </syntaxhighlight> |
|
| |
|
| If you have nested {{codeline|if}} statements, use extra braces for extra clarification. | | If you have nested {{codeline|if}} statements, use extra braces for extra |
| | | clarification. |
| ==== Switch statements ====
| |
| | |
| Indent ''both'' the curly braces and the body of the switch statement (so that the body gets indented by ''two'' indents).
| |
| | |
| However, the {{codeline|case}} statement is not doubly indented and instead aligns with the first brace.
| |
| | |
| <syntaxhighlight lang="cpp">
| |
| switch (info)
| |
| {
| |
| case -1:
| |
| {
| |
| cout << "function failed\n";
| |
| return false;
| |
| }
| |
| | |
| case 0:
| |
| return true;
| |
| }
| |
| </syntaxhighlight>
| |
| | |
| ==== #ifdef directives ====
| |
| | |
| Indent code that follows a conditional processor directive such as {{codeline|#ifdef}} or {{codeline|#else}}.
| |
| | |
| Example
| |
| | |
| <syntaxhighlight lang="cpp">
| |
| #if defined (HAVE_CONFIG_H)
| |
| # include "config.h"
| |
| #endif
| |
| </syntaxhighlight>
| |
| | |
| The '#' character may also be placed with the directive rather than remaining in column 1 if this looks better.
| |
| | |
| ==== Split long expressions ====
| |
|
| |
|
| Split long expressions in such a way that a continuation line starts | | Split long expressions in such a way that a continuation line starts |
Line 112: |
Line 46: |
| </syntaxhighlight> | | </syntaxhighlight> |
|
| |
|
| ==== Optional braces ==== | | === Non indenting whitespace === |
|
| |
|
| Consider putting extra braces around a multi-line expression to make it | | Consider putting extra braces around a multi-line expression to make it |
Line 118: |
Line 52: |
| put extra braces anywhere if it improves clarity. | | put extra braces anywhere if it improves clarity. |
|
| |
|
| === Pointer and Reference appearance ===
| | The negation operator is written with a space between the operator |
| | and its target, e.g., {{codeline|! A}}. |
|
| |
|
| Declarations of pointers have the '*' character cuddled with the ''name'' of the variable. | | Declarations of pointers have the '*' character cuddled with the name of the variable. |
|
| |
|
| <syntaxhighlight lang="cpp"> | | <syntaxhighlight lang="cpp"> |
Line 126: |
Line 61: |
| </syntaxhighlight> | | </syntaxhighlight> |
|
| |
|
| However, references have the '&' character cuddled with the ''type'' of the variable. | | However, references have the '&' character cuddled with the type of the variable. |
|
| |
|
| <syntaxhighlight lang="cpp"> | | <syntaxhighlight lang="cpp"> |
Line 132: |
Line 67: |
| </syntaxhighlight> | | </syntaxhighlight> |
|
| |
|
| === Miscellaneous === | | === Line Length === |
|
| |
|
| The negation operator is written with a space between the operator
| | Keep the length of source lines to 79 characters or less, for maximum |
| and its target, e.g., {{codeline|! A}}.
| | readability in the widest range of environments. This is inherited from |
| | the [https://www.gnu.org/prep/standards/standards.html#Formatting GNU Coding Standards]. |
|
| |
|
| === Function headers === | | === Function headers === |
|
| |
|
| In general, in non-header files, format function headers like this:
| | Format function headers like this: |
|
| |
|
| <syntaxhighlight lang="cpp"> | | <syntaxhighlight lang="cpp"> |
Line 149: |
Line 85: |
| The return type of the function and any modifiers are specified on the first | | The return type of the function and any modifiers are specified on the first |
| line. The function name on the second line should start in column 1, and | | line. The function name on the second line should start in column 1, and |
| multi-line argument lists should be aligned on the first character after the open | | multi-line argument lists should be aligned on the first char after the open |
| parenthesis. Put a space before the left open parenthesis and after | | parenthesis. You should put a space before the left open parenthesis and after |
| commas, for both function definitions and function calls. | | commas, for both function definitions and function calls. |
|
| |
| For header files, or in class definitions, it may look better not to split the return type from the rest of the function header. Use your own judgement.
| |
|
| |
| === Class declarations ===
| |
|
| |
| The access specifier ({{codeline|public}}, {{codeline|protected}}, {{codeline|private}}) should always be stated rather than relying on the C++ language defaults for a particular object (for example, "{{codeline|class}}" = "{{codeline|private}}").
| |
|
| |
| Within a class, the different access blocks should appear in the order 1) {{codeline|public}}, 2) {{codeline|protected}}, 3) {{codeline|private}}.
| |
|
| |
| Within an access block, member functions (methods) should be specified before member variables. If there are both member functions and member variables use
| |
|
| |
| //--------
| |
|
| |
| between the sections to visually separate the two categories.
| |
|
| |
|
| === Namespace === | | === Namespace === |
|
| |
|
| All code should be in the {{codeline|octave}} namespace or in a namespace below it. | | All code should be in the octave namespace. This is an ongoing project. We |
| | are still moving existing classes into namespaces but all new classes |
| | should go somewhere into the "octave" namespace. There is 1 extra level for namespaces |
| | inside octave to be used with care, we don't want too many namespaces. |
| | Ask before creating a new namespace. |
|
| |
|
| Namespaces should start and stop using the special macros {{codeline|OCTAVE_BEGIN_NAMESPACE(XXX)}} and {{codeline|OCTAVE_END_NAMESPACE(XXX)}}. There is no indentation of code that is placed into namespaces using these macros.
| | * Indent namespaces as any other block. Emacs and other editors can do this automatically. |
| | * Define namespace on the .cc files; |
| | * Do not use "using X" directives; |
| | * Do not declare anything on the std namespace; |
|
| |
|
| Example
| | {{Code|namespace style on a .h file|<syntaxhighlight lang="cpp"> |
| | | // Note indentation |
| {{Code|Use of namespace macros|<syntaxhighlight lang="cpp"> | | namespace octave |
| OCTAVE_BEGIN_NAMESPACE(octave)
| | { |
| | | namespace math |
| OCTAVE_BEGIN_NAMESPACE(math)
| | { |
| | | class foo |
| template <typename T>
| | { |
| void
| | public: |
| umfpack_report_control (const double *Control);
| | foo (...); |
| | | }; |
| OCTAVE_END_NAMESPACE(math)
| | } |
| OCTAVE_END_NAMESPACE(octave)
| | } |
| </syntaxhighlight>}} | | </syntaxhighlight>}} |
|
| |
|
| If bare namespace directives must be used, as occasionally is required in Qt code, then the code within the namespace should be indented.
| | {{Code|namespace style on a .cc file|<syntaxhighlight lang="cpp"> |
| | | // Note indentation and that functions are not defined |
| {{Code|bare namespace usage|<syntaxhighlight lang="cpp"> | | // as "octave::math::foo:foo" |
| // Note indentation and that functions are not defined as "octave::math::foo:foo" | |
| namespace octave | | namespace octave |
| { | | { |
Line 203: |
Line 131: |
| } | | } |
| </syntaxhighlight>}} | | </syntaxhighlight>}} |
|
| |
| ==== Other Guidelines ====
| |
| * Do not use {{codeline|using XXX;}} directives
| |
| * Do not declare anything on the {{codeline|std::}} namespace
| |
|
| |
|
| == Naming == | | == Naming == |
|
| |
|
| Use lowercase names if possible. Uppercase is acceptable for variable names consisting of 1-2 letters. Do not use mixed case (a.k.a. CamelCase) names. | | Use lowercase names if possible. Uppercase is acceptable for variable |
| | | names consisting of 1-2 letters. Do not use mixed case names. |
| === Member Variables ===
| |
|
| |
|
| Member variables should use the prefix "m_" whenever possible.
| |
|
| |
| === Class Variables ===
| |
|
| |
| Class variables should use the prefix "s_" (for "static") whenever possible.
| |
|
| |
| === Filenames ===
| |
|
| |
| As with m-files, the file name of a C++ source file containing a class should match the name of the class defined within the file. For example, "password.h" defines the class "password" rather than "passwd.h" which is a common abbreviation for "password".
| |
|
| |
|
| == Header Files == | | == Header Files == |
Line 260: |
Line 174: |
| == C++ features == | | == C++ features == |
|
| |
|
| === references === | | === C++11 features === |
| | |
| Use references when passing variables that will be changed by a subroutine rather than the C-style method of passing pointers.
| |
|
| |
|
| {| class="wikitable"
| | C++11 features are generally allowed. Check if the feature you want to |
| ! style="color:green;" | good
| | use has been already used. If not, ask on the mailing list. |
| ! style="color:darkred;" | bad
| |
| |-
| |
| | <syntaxhighlight lang="c++">
| |
| void foo (int& a_ref)
| |
| {
| |
| // foo changes content of `a_ref`
| |
| a_ref = a_ref + 1;
| |
| }
| |
| | |
| void bar ()
| |
| {
| |
| int a = 42;
| |
| foo (a);
| |
| }
| |
| </syntaxhighlight>
| |
| | <syntaxhighlight lang="c++">
| |
| void foo (int *a_ptr)
| |
| {
| |
| // foo changes content of `a_ptr`
| |
| *a_ptr = *aptr + 1;
| |
| }
| |
| | |
| void bar ()
| |
| {
| |
| int a = 42;
| |
| foo (&a);
| |
| }
| |
| </syntaxhighlight>
| |
| |}
| |
| | |
| When passing variables that are large, but will not be changed in a subroutine (read-only), use {{codeline|const}} references. This helps avoid overflowing the finite stack capacity of a program while still ensuring that read-only access is enforced.
| |
| | |
| {| class="wikitable"
| |
| ! style="color:green;" | good
| |
| ! style="color:darkred;" | bad
| |
| |-
| |
| | <syntaxhighlight lang="c++">
| |
| void foo (const std::string& str_ref)
| |
| {
| |
| // foo does not change content of `str_ref`
| |
| }
| |
| | |
| void bar ()
| |
| {
| |
| std::string str ("This is a large variable, however as a reference it will take up just 8 bytes on the stack when passed to the subroutine foo()");
| |
| foo (str);
| |
| }
| |
| </syntaxhighlight>
| |
| | <syntaxhighlight lang="c++">
| |
| void foo (std::string str_copy)
| |
| {
| |
| // foo does not change content of `str_copy`
| |
| }
| |
| | |
| void bar ()
| |
| {
| |
| std::string str ("This is a large variable that will be copied on to the stack and passed as a temporary variable to the subroutine foo()");
| |
| foo (str);
| |
| }
| |
| </syntaxhighlight>
| |
| |}
| |
| | |
| === new/delete ===
| |
| | |
| Pointers that will be allocated memory with {{codeline|new}} should be initialized with the C++ literal {{codeline|nullptr}}, not the numerical value 0 or the macro {{codeline|NULL}}.
| |
| | |
| The {{codeline|delete}} keyword accepts {{codeline|nullptr}} and programmers should not put an {{codeline|if (ptr)}} guard around {{codeline|delete}}.
| |
| | |
| {| class="wikitable"
| |
| ! style="color:green;" | good
| |
| ! style="color:darkred;" | bad
| |
| |-
| |
| | <syntaxhighlight lang="c++">
| |
| delete ptr;
| |
| </syntaxhighlight>
| |
| | <syntaxhighlight lang="c++">
| |
| if (ptr)
| |
| delete ptr;
| |
| </syntaxhighlight>
| |
| |}
| |
| | |
| === lambda expressions ===
| |
| | |
| When capturing variables from the surrounding function, explicitly list the variables being captured rather than relying on a default capture by value (`[=]`) or by reference (`[&]`). This more clearly captures the programmer's intent and makes the code more understandable.
| |
|
| |
|
| === std::string === | | === std::string === |
|
| |
|
| When an empty string is required, use <code>""</code>, rather than creating an empty | | When an empty string is required, use "", rather than creating an empty |
| string object with <code>std::string ()</code>. | | string object with std::string (). |
|
| |
|
| === auto === | | === auto === |
Line 369: |
Line 197: |
| Always use one of the four C++ long style casting forms ({{codeline|static_cast}}, {{codeline|dynamic_cast}}, {{codeline|reinterpret_cast}}, {{codeline|const_cast}}) rather than C-style forms (type cast {{codeline|(new_type) variable}} or the function form {{codeline|new_type (variable)}}). | | Always use one of the four C++ long style casting forms ({{codeline|static_cast}}, {{codeline|dynamic_cast}}, {{codeline|reinterpret_cast}}, {{codeline|const_cast}}) rather than C-style forms (type cast {{codeline|(new_type) variable}} or the function form {{codeline|new_type (variable)}}). |
|
| |
|
| === C++11 features ===
| | === C++14 === |
| | |
| A C++11 compatible compiler is required for [[Building | building Octave]]. Please make use of all C++11 features.
| |
| | |
| === C++14, C++17, C++20 features === | |
|
| |
|
| Try to avoid C++14, C++17, or C++20 features. Octave is widely used in very old systems and we want them to be able to use up to date versions of Octave. Building a recent compiler in such systems is not a trivial task so the limitation must happen
| | Do not use C++14 features. Octave is widely used in very old systems and we |
| | want them to be able to use up to date versions of Octave. Building a recent |
| | compiler in such systems is not a trivial task so the limitation must happen |
| in Octave. | | in Octave. |
|
| |
|
| If the implementation using a C++14, C++17, or C++20 feature is very beneficial, make it optional via <code>configure</code> feature detection or also implement an alternative code in the absence of said feature. In any case, please get in contact with the Octave maintainers on [https://octave.discourse.group/c/maintainers/7 Discourse].
| | An exception: code that requires C++14 feature must also implement an |
| | alternative code in the absence of said feature. In such case, use a |
| | configure check. This increases maintenance a lot, must be used sparsely, |
| | and requires approval from other maintainers. |
|
| |
|
| <syntaxhighlight lang="cpp"> | | <syntaxhighlight lang="cpp"> |