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view STYLE.md @ 35:6114710feda7
Add paragraph about code in headers
author | David Demelier <markand@malikania.fr> |
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date | Mon, 30 Jul 2018 14:31:58 +0200 |
parents | 3bf129646979 |
children | a77a41f83ebb |
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PROJECT NAME CODING STYLE ========================= General ======= - Always use 4 spaces as indentation (expect Makefiles), - Use UTF-8 charset, - Use Unix line endings, - Never write two blank consecutives blank lines, C++ === Style ----- - Do not exceed 120 characters for lines of code, - Do not exceed 80 characters for comments, ### Braces Braces follow the K&R style, they are never placed on their own lines except for function definitions. Do not put braces for single line statements. ```cpp if (condition) { apply(); add(); } else ok(); if (condition) validate(); if (foo) state = long + conditional + that + requires + several + lines + to + complete; ``` Functions require braces on their own lines. ```cpp void function() { } ``` And a lambda has its braces on the same lines too: ```cpp sort([&] (auto&) { return true; }); ``` ### Spaces Each reserved keyword (e.g. `if`, `for`, `while`) requires a single space before its argument. Normal function calls do not require it. ```cpp if (foo) destroy(sizeof (int)); ``` ### References and pointers References and pointers are always next to the type name and not the variable. ```cpp auto get(const std::string& name) -> T&; int* p = &x; ``` ### Trailing return syntax We use trailing return syntax everywhere, it has the following benefits: - Inner types don't need to be prefixed by class name, - Functions are kept aligned correctly, focusing on the function name. ```cpp auto func() -> std::string; ``` ### Naming - English names, - Member variables have trailing underscore (e.g foo\_bar\_), - No hungarian notation. Everything is in `underscore_case` except template parameters and macros. ```cpp #if defined(FOO) # include <foo.hpp> #endif namespace baz { class object { private: std::string name_; public: auto name() const noexcept -> const std::string&; }; template <typename Archive> void open(const Archive& ar) { bool is_valid = false; } } // !baz ``` ### Header guards Do not use `#pragma once`. Header guards are usually named `PROJECT_COMPONENT_FILENAME_HPP`. ```cpp #ifndef FOO_COMMON_UTIL_HPP #define FOO_COMMON_UTIL_HPP #endif // !FOO_COMMON_UTIL_HPP ``` ### Enums Enumerations constants are always defined in separate line to allow commenting them as doxygen. Enum class are encouraged. ```cpp enum class color { blue, red, green }; ``` ### Switch In a switch case statement, you **must** not declare variables and not indent cases. ```cpp switch (variable) { case foo: do_some_stuff(); break; default: break; } ``` ### Files - Use `.cpp` and `.hpp` as file extensions, - Filenames are all lowercase. ### Comments Avoid useless comments in source files. Comment complex things or why it is done like this. However any public function in the .hpp **must** be documented as doxygen without exception. ```cpp /* * Multi line comments look like * this. */ // Short comment ``` Use `#if 0` to comment blocks of code. ```cpp #if 0 broken_stuff(); #endif ``` ### Includes The includes should always come in the following order. 1. C++ headers 2. C header 3. Third party libraries 4. Application headers in "" ```cpp #include <cstring> #include <cerrno> #include <sys/stat.h> #include <libircclient.h> #include "foo.h" ``` Note: always use C++ headers for C equivalent, stdio.h -> cstdio, etc. Programming ----------- ### C language Do not use old C stuff like `void *`, `srand/rand`, `printf` or anything that can be rewritten in modern C++. ### RTTI Usage of `dynamic_cast` and `typeid` are completely disallowed in any shape of form. ### Arguments It is recommended to pass parameters by value or const reference. Usage of non-const reference as output parameter is **discouraged** and should be avoided in many case because it does not allow chaining of expressions like: ```cpp std::cout << reverse(upper(clean(" hello world! "))) << std::endl; ``` If your function is designed to return a modified value passed as argument, it is better to take it by value and modify it directly. ```cpp auto clean(std::string input) -> std::string { if (!input.empty() && input.back() == '\r') input.pop_back(); return input; } ``` Never pass primitive types as const value. ### Assertions Use the `assert` macro from the cassert header file to verify programming errors. For example, you may use `assert` to verify that the developer access the data between the bounds of an array: ```cpp auto operator[](unsigned index) -> T& { assert(index < length_); return data_[index]; } ``` The `assert` macro is not meant to check that a function succeeded, this code must not be written that way: ```cpp assert(listen(10)); ``` ### Exceptions You must use exceptions to indicate an error that was unexpected such as: - Failing to open a file, - I/O unexpected errors, - Parsing errors, - User errors. You may use the C++ standard exceptions defined in the stdexcept header but if you need to carry more data within your exception, you should derive from `std::exception`. ### Error code You should not use error codes to indicate errors, instead use exceptions. Error codes are allowed in Boost.Asio though. ### Free functions Basic utility functions should be defined in a namespace as a free function not as a static member function, we're doing C++ not Java. Example: ```cpp namespace util { auto clean(std::string input) -> std::string } // !util ``` ### Variables initialization Use parentheses to initialize non primitive types: ```cpp throw std::runtime_error("foo"); my_class obj("bar"); ``` Use brace initialization when you want to use an initializer list, type elision: ```cpp std::vector<int> v{1, 2, 3}; foo({1, 2}); // type deduced return { "true", false }; // std::pair returned ``` Use the assignment for primitive types: ```cpp int x = 123; bool is_valid = true; ``` ### Classes Classes are usually defined in the following order: 1. Public inner types (enums, classes), 2. Protected/private members and functions 3. Public static functions. 3. Public member functions 4. Public virtual functions. ```cpp class foo { public: enum class type { a, b }; private: int member_{0}; public: void some_function(); }; ``` ### Structs Use structs for objects that only need to store public data and have no invariants. For example PODs and traits match this criteria: ```cpp struct point { int x{0}; int y{0}; }; template <> struct info_traits<point> { template <typename Archive> static void serialize(Archive& ar, const point& point) { ar.write(point.x); ar.write(point.y); } }; ``` ### Return The preferred style is to return early in case of errors. That makes the code more linear and not highly indented. This code is preferred: ```cpp if (a_condition_is_not_valid) return nullptr; if (an_other_condition) return nullptr; auto x = std::make_shared<object>(); x->start(); x->save(); return x; ``` Additional rules: - Do never put parentheses between the returned value, - Do not put a else branch after a return. ### Auto We encorage usage of `auto`, it reduces code maintainance as you don't need to change your code when your rename types. ```cpp auto it = std::find_if(v.begin(), v.end(), [&] (const auto& obj) { return obj.key() == "foo"; }); for (const auto& pair : a_map) std::cout << pair.first << " = " << pair.second << std::endl; ``` But do not use `auto` to write code like in python, this is not acceptable: ```cpp auto o = my_object("foo"); ``` ### String views Use `std::string_view` each time you need a string that you will not own, this includes: temporary arguments, return values, compile time constants. ```cpp const std::string_view version("1.0"); void load(std::string_view id, std::string_view path) { std::cout << "loading: " << id << " from path: " << path << std::endl; } ``` ### Optional values Use `std::optional` to indicate a null value considered as valid. For example, searching a value that may not exist. ```cpp auto find(std::string_view id) -> std::optional<int> { if (auto it = foo.find(id); it != foo.end()) return it->second; return std::nullopt; } ``` ### Avoid definitions in headers Try to avoid as much as possible function definition in header file. It slow down compilation because the compiler has to parse the syntax over and over. It's even worse as you may need to recompile a lot of files when you change a header rather than a source file. CMake ===== Style ----- - Try to keep line shorter than 80 columns ### Spaces Each programming keyword (e.g. `if`, `foreach`, `while`) requires a single space before its argument, otherwise write opening parenthese directly after. ```cmake foreach (c ${COMPONENTS}) string(TOUPPER ${c} CMP) if (${WITH_${CMP}}) add_executable(${c} ${c}.cpp) endif () endforeach () ``` ### Line breaks When CMake lines goes too long, you should indent arguments at the same level, it's also common to see named argument values indented even more. ```cmake set( FILES ${myapp_SOURCE_DIR}/main.cpp ${myapp_SOURCE_DIR}/foo.cpp ${myapp_SOURCE_DIR}/bar.cpp ) command_with_lot_of_arguments( TARGET foo INSTALL On SOURCES ${myapp_SOURCE_DIR}/main.cpp ${myapp_SOURCE_DIR}/foo.cpp ${myapp_SOURCE_DIR}/bar.cpp COMMENT "Some comment" ``` Modern CMake ------------ CMake evolves over time, if you have read very old articles there is a chance that what you have read is actually deprecated and replaced by other features. The following list is a short summary of modern CMake features that you must use. ### Imported targets When they are available, use imported targets rather than plain variables. They offer complete dependency tracking with options and include directories as well. ```cmake find_package(Boost COMPONENTS system) target_link_libraries(main Boost::system) ``` ### Use generator expressions Use generator expressions as much as you can, they offer much more flexibility in case of multiple generators. Remember that CMake is not meant to be used only with Makefiles. ```cmake target_link_libraries( myapp $<$<STREQUAL:${CMAKE_SYSTEM_NAME},Windows>:shlwapi> $<$<STREQUAL:${CMAKE_SYSTEM_NAME},Linux>:dl> ``` Warning: do never test against `CMAKE_BUILD_TYPE` in any CMakeLists.txt, IDEs like Visual Studio will mismatch what you'll put in the conditions. ### Avoid global scoping The following commands must be avoided as much as possible: - `link_directories`, - `link_libraries`, - `include_directories`, - `add_definitions`. They pollute the global namespace, all targets defined after these commands will be built against those settings. Instead, you should use the per-targets commands. ```cmake target_include_directories( mylib PUBLIC $<BUILD_INTERFACE:${mylib_SOURCE_DIR}> $<INSTALL_INTERFACE:include> ) target_link_libraries(mylib foo) ``` ### Defining sources You MUST never use any kind of `file(GLOB)` commands to list sources for an executable. CMake is designed to be re-called by itself only when required, having such a construct will not let CMake be able to detect if you have added/removed files in your source directory. Instead, you MUST always specify all source by hands. ```cmake set( FILES ${myapp_SOURCE_DIR}/main.cpp ${myapp_SOURCE_DIR}/a.cpp ${myapp_SOURCE_DIR}/b.cpp ) add_executable(myapp ${FILES}) ``` Markdown ======== Lists ----- Use hyphens for unordered lists for consistency, do not indent top level lists, then indent by two spaces each level ```markdown - unordered list 1 - unordered list 2 - sub unordered item 1. unordered list 1 2. unordered list 2 2.1. sub unordered item ``` Code blocks ----------- You can use three backticks and the language specifier or just indent a block by for leading spaces if you don't need syntax. ```cpp std::cout << "hello world" << std::endl; ``` And without syntax: ```markdown This is simple code block. ``` Tables ------ Tables are supported and formatted as following: ```markdown | header 1 | header 2 | |----------|----------| | item 1 | item 2 | ``` Alerts ------ It's possible to prefix a paragraph by one of the following topic, it renders a different block depending on the output format: - Note: - Warning: - Danger: Then, if the paragraph is too long, indent the text correctly. ```markdown Note: this is an information block that is too long to fit between the limits so it is split and indented. ```