Coding Styleguide » History » Revision 8
Revision 7 (quintus, 03/21/2020 12:32 PM) → Revision 8/17 (quintus, 03/24/2020 10:53 AM)
# Coding Styleguide
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Those who have worked on the TSC project will remember the dreaded discussion about coding style. This project will avoid the trap by using a consistent coding style right from the start. It is outlined in this document.
The game's source code is formatted mostly according to the [1TBS](http://astyle.sourceforge.net/astyle.html#_style=1tbs) [1TBS](https://en.wikipedia.org/wiki/Indentation_style#Variant:_1TBS_(OTBS)) style, which is a variant of K&R, with slight adjustments. Details are documented below. Most (not all!) rules can be followed by formatting with the [astyle](http://astyle.sourceforge.net) command like this:
~~~~
$ astyle --style=1tbs --indent=spaces=4 --indent-namespaces \
--attach-classes --attach-namespaces --attach-closing-while --attach-extern-c \
--align-pointer=type --align-reference=type \
--break-one-line-headers --add-braces --close-templates \
yourfile.cpp
~~~~
In general, try to keep your code readable. Specifically, it is often useful to leave empty lines to separate logically grouped statements from one another.
## Indentation, line length
One of the design goals of this document Source code is to keep the styling consequent indented with 4 spaces, tabs are not used. Lines should be broken around 80 characters, and easy to follow. For instance, instead of the questionable distinction of attaching braces to structs, but not to classes in the 1TBS style, this style says to simply always attach the braces (the only exception being function definitions). In resulting continuation lines should be indented so far that it includes elements from the Stroustrup style. Likewise, indenting every brace block is easier makes sense to remember than not to indent namespaces. look at. Example:
~~~~~ c++
if (somecondition) {
thisIsAVeryLongFunctionName(this_is_a_parameter,
this_is_another_parameter,
third_parameter);
}
~~~~~
## Commentary
Semantically, comments should normally reflect why code is written the way it is. Normally it is not required to explain what code does, unless it is an exceptionally complex part. Syntactically, use `//` for one and two lines of comments. Starting with the third line, comments should use the bock syntax `/* ... */`. In the block syntax, align each star with the one on the preceeding line. Terminate the comment block on the last line of the comment.
~~~~~ c++
// Careful: this is used in foobar() as well
/* This code is designed to specifically fit the purpose of an example.
* It was not at all easy to come up with all this text, but for the
* sake of an example, it was required to do so. */
~~~~~
### Documentation comments
Where Doxygen is used to generate documentation, use Doxygen's `///` markers for short and the `/**` markers for long documentation. Other than that, the above advice applies.
## Indentation and line length
Source code is indented with 4 spaces, tabs are not used. All blocks enclosed in braces are indented, including namespaces. Do not indent labels, including visibility labels like `public` and `private`; they should line up with the enclosing statement. Preprocessor statements are not indented.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ c++
#ifndef MY_HEADER
#define MY_HEADER
namespace MyNamespace {
class MyClass {
public:
MyClass();
~MyClass();
};
struct mystruct {
int a;
int b;
};
}
void MyFunc()
{
foo();
if (something) {
bar();
baz();
}
}
#endif
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Lines should be broken around 80 characters, and the resulting continuation lines should be indented so that it makes sense to look at. Example:
~~~~~ c++
if (somecondition) {
thisIsAVeryLongFunctionName(this_is_a_parameter,
this_is_another_parameter,
third_parameter);
}
~~~~~
This is not a hard requirement. You should use whatever conveys the meaning best. That's why the `astyle` command above does not include a hard line wrap option.
## Placement of braces
Braces are placed on the same line like the statement they belong to, be that a class or namespace declaration, an `extern C`, or anything else. The only exception from this are function definitions: for them the opening brace is broken into the next line. In any case, the closing brace always has its own line (makes it easy to spot the end of a block). `if/elseif/else` is cuddled to keep code compact, and the rare case of a trailing `while` has the `while` attached to the brace. Do not leave out braces even for one-line statements. This should prevent any accidental cutting of conditional clauses. To keep style consistent, also do not use all-in-one-line conditionals (this violates the expectation that the closing brace for each block can be found on its own line at the relevant indentation level).
Keen readers will notice that for in-function statements this uses the 1TBS style, and for out-of-function statements the Stroustrup style. Examples below.
~~~~~~~~~~~ c++
// Exception: function definition
void main()
{
// ...
}
// Everything else: attach the braces.
class Foo {
// ...
};
struct foo {
// ...
};
enum class foo {
// ...
};
if (condition) {
// ...
}
while (condition) {
// ...
}
// Trailing while attached
{
// ...
} while (condition)
// Brace kuddling from 1TBS
if (condition1) {
// ...
} else if (condition2) {
// ...
} else {
// ...
}
// Required braces around one-line statements
if (condition) {
doit();
}
// Also requires braces
if (condition1) {
doit();
} else { // Thanks to brace cuddling, this is not as bad as in pure K&R
doother();
}
// DO NOT DO THIS
if (condition) { oneliner(); }
// Break it.
if (condition) {
oneliner();
}
~~~~~~~~~~~
## Initial assignment
Assign an initial value to any variable you declare. This prevents undefined values from coming from a forgotten assignment and eases debugging quite a bit, because it obviates the question "is this a real value or was this variable never assigned?".
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ c++
int a; // BAD
int a = 0; // GOOD
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
## Pointer and reference alignment, multi-variable declarations
Place the `*` and `&` next to the type, not to the name. They belong semantically to the type. Do not declare multiple variables in one line if one of them is a pointer, it causes confusion:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ c++
int i = 0, j = 0; // Okay, no pointer
int* p = nullptr; // Pointer to int
int* p1 = nullptr, p2 = 0; // DONT DO THIS. p2 is not a pointer!
// Instead, break the lines up.
int* p1 = nullptr;
int p2 = 0;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Multiple variable assignments should be aligned at the `=`.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ c++
int foo = 0;
int foobar = 0;
int la = 0;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
## Parantheses and spacing
Between a keyword and the opening paranthesis is exactly one space. Between the closing paranthesis and the opening curly brace is exactly one space as well. *There is no space between a function name and the opening paranthesis of its argument list*.
Template angles and index brackets do not have any surrounding space.
~~~~~~~~ c++
void Foo(int myparam) // No spaces around the "(" and ")"
{
if (condition) { // One space between keyword if and "(", and one space between ")" and "{"
MyFunc(5); // No spaces around the "(" and ")"
}
}
vector[3] = foo; // No space between "vector" and "[3]"
map<string, vector<int>> mymap; // No spaces around <> (C++11 syntax)
~~~~~~~~
## Case of identifiers
* Macros are ALL_IN_CAPS. They need to stand out.
* Class identifiers use CamelCase. Structure and enum identifiers are snake_case (makes it easy to spot whether this type is copy-by-value or copy-by-reference: every lowercase type is copy-by-value).
* Member function identifiers are CamelCase. This keeps function names short (they tend to be longer than member variable names).
* All variables and constants (unless the constants are macros, see above) are snake_case. This includes static member variables, even if they are constant. This way a non-function member is easily identifiable by being lowercase. The different variable types are distinguished by the prefix (see [below](#Abbreviated-Hungarian-Notation)).
~~~~~~ c++
#define THIS_IS_A_MACRO(x) foo_ ## x
struct my_struct;
enum class my_enum;
class MyClass {
MyClass();
~MyClass();
void MemberFunction();
static int StaticMemberFunction();
int m_member_variable;
static int static_member;
};
void foo()
{
static int local_static_variable;
float normal_local_var = 3.5f;
// ...
}
~~~~~~
## Abbreviated Hungarian Notation
Identifiers of variables and constants begin with a short sequence of characters that encodes some important information about the variable in question. This is called [Hungarian Notation](https://en.wikipedia.org/wiki/Hungarian_notation), but in full, it is cumbersome to read and leads to long identifier names. The following prefix characters have been chosen with respect to two goals: Make variable scope immediately visible, and warn of "unusual" types.
| Prefix | Meaning |
|--------+------------------------------------------------------------------|
| | No prefix: Local variable |
| m | Member variable |
| f | File-local variable |
| g | Global variable |
| p | Variable holds a pointer (both raw and managed pointers) |
| a | Variable holds a raw array (not: vector or other C++ containers) |
The scope prefix comes before the type prefix. Thus, `mp_foo` is a member variable holding a pointer, and `ga_argv` is a global variable holding a raw C array.
There are two special cases. First, member variables of structs and enums do not have a leading `m` prefix, because they do not normally contain functions, but are only accessed from the outside (whereas for classes as per the secrecy principle access to member variables from the outside is unusual), and it would be cumbersome to always add the extra `m`. Second, static member variables of classes do not have a scope prefix. Instead, they are always to be accessed via the class name.
~~~~~~~~~~~ c++
static int f_something; // File-local variable
extern int g_globvar; // Global variable
class MyClass {
void MyFunc()
{
int* p_int; // Local variable
m_normal_member += "AAA"; // Accessing member variable
DoSomething(MyClass::foobar); // Exception: accessing static member variable via class name, not directly
}
std::string m_normal_member; // Normal member variable
int* mp_int; // Member variable with pointer
static const float foobar = 42; // Exception: Static member variable
};
struct point {
int x; // Struct members have no "m" prefix
int y;
int z;
owner* p_owner; // But they do have the type prefix if required.
};
point MoveUp(point p)
{
p.y -= 10; // Access to struct member without "m"
return p;
}
enum class color { red, green, blue }; // Exception: enum members do not have "m"
void MyFunc(color c)
{
if (c == color::red) { // Because they are accessed only from the outside.
// ...
}
}
~~~~~~~~~~~
## Compound Statements
The opening brace resides on the same line as the statement it applies to, regardless of whether this is a function, a control flow statement, or a class or enum declaration. The closing brace has a line on its own to ensure it is easily spottable where a block ends.
~~~~~~~~~~~ c++
class Foo {
};
if (condition) {
// ...
}
while (condition) {
// ...
}
void main() {
// ...
}
~~~~~~~~~~~
The rare case of a terminal `while` has the `while` after the closing brace on the same line.
~~~~~~ c++
{
// ...
} while (condition)
~~~~~~~
## Brace Cuddling
In an if/elsif/else statement, braces are cuddled to keep code compact.
~~~~~~~~~~ c++
if (condition1) {
// ...
} else if (condition2) {
// ...
} else {
// ...
}
~~~~~~~~~~~
## Braces around short statements
Do not leave out braces even for one-line statements. This should prevent any accidental cutting of conditional clauses.
~~~~~~~~~ c++
// Short: required braces
if (condition) {
doit();
}
// Also requires braces
if (condition1) {
doit();
} else { // Thanks to brace cuddling, this is not as bad as in pure K&R
doother();
}
// Requires braces in any style to keep clarity
if (condition1) {
doit();
} else {
doother1();
if (condition2) {
something();
}
else {
andmore();
}
}
~~~~~~~~~
## Parantheses and spacing
Between a keyword and the opening paranthesis is exactly one space. Between the closing paranthesis and the opening curly brace is exactly one space as well. *There is no space between a function name and the opening paranthesis of its argument list*, neither in declaration nor in calling of a function.
~~~~~~~~ c++
void Foo() { // No space between function name and (, but one space between ) and {
if (condition) { // One space between keyword if and (, and one space between ) and {
// ...
}
}
~~~~~~~~
## Visibility Specifiers
In class declarations, visibility labels like `public` and `private` are on the same level like the corresponding `class` statement.
~~~~~~~ c++
class MyClass {
public:
MyClass();
~MyClass();
private:
void PrivateMethod();
};
~~~~~~~
## enum specifics
Names of `enum` identifiers are singular, not plural. If used as a type, `color var` reads more natural than `colors var`. Use `enum class` instead of raw `enum` whenever possible (this is C++11 specific and allows colliding enum identifiers in case you wonder that `enum class` is valid syntax).
~~~~~~ c++
enum class color { red, green, blue };
void Foo(color c)
{
// ...
}
~~~~~~
## File names
All source code files are in snake_case. C++ source code files end in `.cpp`, C++ headers end in `.hpp`. C source files end with `.c`, C headers in `.h`.
## Inclusion of headers
Each C/C++ source file includes only the headers it needs to compile, and all inclusions are at the top of the file. Inclusions are done in this order:
1. The header file corresponding to this `.c`/`.cpp` file. Doing this first ensures that the `.hpp` file is self-contained, because on compilation of the corresponding `.cpp` file the compiler will error out on the very first `#include` line then if the header is not self-contained. For `.hpp` files, this step is obviously missing.
2. Other internal headers.
3. External library headers.
4. Standard library headers.
The path delimiter for `#include` statements is always a forward slash, because this compiles on both Windows and Unix systems. External and standard library headers are included with angle `#include <>`, internal headers with quoted `#include ""`.
~~~~~~~ c++
// This is foo.cpp, it has a header foo.hpp.
#include "foo.hpp"
#include "../misc/internal_header.hpp"
#include <curl.h>
#include <vector>
#include <cstdlib>
~~~~~~~
## Forward declarations in headers
To increase compile times and keep the inclusion graph simple, headers should try hard to not require other internal headers. If an internal type is required in a header, it should be forward-declared in that very header. Note that it is possible to forward-declare classes, structs, and even enums. In most cases, forward-declarations are entirely sufficient. For instance, pointers, references, many templated types, and even smart pointers can be used with only the forward-declaration available.
~~~~~~~~~~ c++
// Forward declarations
class MyClass;
class MyOtherClass {
public:
MyOtherClass(MyClass& mc) : m_mc(mc){} m_mc(mc) {}
void Foo(MyClass* p_mc){ /* ... */ }
private:
MyClass& m_mc;
};
~~~~~~~~~~
The corresponding `.cpp` file will then have to include the internal header for `MyClass`:
~~~~~~ c++
#include "my_other_class.hpp"
#include "../misc/my_class.hpp" // <---
~~~~~~