Difference between revisions of "Code style guidelines"

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[[Category:Core]]
+
This is the coding style used for C/C++ code. Also see the [[Lua code style guidelines]].
 +
 
 +
The coding style is based on the [https://www.kernel.org/doc/html/latest/process/coding-style.html Linux kernel code style]. Much of the existing code doesn't follow the current code style guidelines, do not try to replicate that. Use your best judgment for C++-specific syntax.
 +
 
 +
Currently, the code uses C++17. Do not use features that depend on more recent versions.
 +
 
 +
=== Spelling ===
 +
 
 +
Use American English, but avoid idioms that may be difficult to understand by non-native speakers.
 +
 
 +
=== Function declarations ===
 +
 
 +
In case your function parameters don't fit within the defined line length, use the following style.
 +
Indention for continuation lines is '''exactly''' two tabs.
 +
 
 +
<source lang="cpp">
 +
void some_function_name(type1 param1, type2 param2, type3 param3,
 +
type4 param4, type5 param5, type6 param6, type7 param7)
 +
{
 +
...
 +
}
 +
</source>
 +
 
 +
Sometimes with complex function declarations, it might be messy to define as many parameters as possible on the same line.
 +
This is acceptable too (and currently used in some places):
 +
 
 +
<source lang="cpp">
 +
void some_function_name(
 +
const ReallyBigLongTypeName &param1,
 +
ReallyBigLongTypeName *param2,
 +
void *param3,
 +
size_t param4,
 +
const void *param5,
 +
size_t param6)
 +
{
 +
...
 +
}
 +
</source>
 +
 
 +
No more than 7 parameters allowed (except for constructors).
  
For everybody else's sanity, please just use something that resembles the [https://www.kernel.org/doc/Documentation/CodingStyle Linux Kernel code style], with the exception that cases in switch statements are indented a level. Much of the already existing code is somewhat weird looking and breaks the current code guidelines, do not try to replicate that. Use your best judgement for C++-specific syntax.
 
 
=== Spaces ===
 
=== Spaces ===
* <span style="color: red">Do '''not''' use spaces for indentation.</span>
+
 
 +
* <span style="color: red">Do '''not''' use spaces to indent.</span>
 
* Try to stay under 6 levels of indentation.
 
* Try to stay under 6 levels of indentation.
* Do add spaces between operators so they line up when appropriate (don't go overboard). For example:
+
* Add spaces between operators so they line up when appropriate (don't go overboard). For example:
np_terrain_base  = settings->getNoiseParams("mgv6_np_terrain_base");
+
 
np_terrain_higher = settings->getNoiseParams("mgv6_np_terrain_higher");
+
<source lang="cpp">
np_steepness      = settings->getNoiseParams("mgv6_np_steepness");
+
np_terrain_base  = settings->getNoiseParams("mgv6_np_terrain_base");
np_height_select  = settings->getNoiseParams("mgv6_np_height_select");
+
np_terrain_higher = settings->getNoiseParams("mgv6_np_terrain_higher");
...
+
np_steepness      = settings->getNoiseParams("mgv6_np_steepness");
bool success =
+
np_height_select  = settings->getNoiseParams("mgv6_np_height_select");
np_terrain_base  && np_terrain_higher && np_steepness &&
+
...
np_height_select && np_trees          && np_mud      &&
+
bool success =
np_beach        && np_biome          && np_cave;
+
np_terrain_base  && np_terrain_higher && np_steepness &&
 +
np_height_select && np_trees          && np_mud      &&
 +
np_beach        && np_biome          && np_cave;
 +
</source>
 +
 
 
The above code looks really nice.
 
The above code looks really nice.
 
* Separate different parts of functions with newlines for readability.
 
* Separate different parts of functions with newlines for readability.
 
* Separate functions by two newlines (not necessary, but encouraged).
 
* Separate functions by two newlines (not necessary, but encouraged).
=== Do not be too C++y ===
+
* Use a space after <code>if</code>, <code>else</code>, <code>for</code>, <code>do</code>, <code>while</code>, <code>switch</code>, <code>case</code>, <code>try</code>, <code>catch</code>, etc.
* Don't use references when they're not necessary.  They are rather inflexible and can be misleading.
+
* When breaking conditionals, indent following lines of the conditional with two tabs and the statement body with one tab. For example:
 +
 
 +
<source lang="cpp">
 +
for (std::vector<std::string>::iterator it = strings.begin();
 +
it != strings.end();
 +
++it) {
 +
*it = it->substr(1, 1);
 +
}
 +
</source>
 +
 
 +
* Align backslashes for multi-line macros with spaces:
 +
 
 +
<source lang="cpp">
 +
#define FOOBAR(x) do {    \
 +
int __temp = (x); \
 +
foo(__temp);      \
 +
} while (0)
 +
</source>
 +
 
 +
=== Bracing and indentation ===
 +
==== <code>if</code> statements ====
 +
This rule has already been explicitly stated in the [https://www.kernel.org/doc/html/latest/process/coding-style.html Linux kernel code style] from which this code style inherits, but it will be repeated here:
 +
 
 +
<span style="color: red">'''Putting the body of an <code>if</code> statement on the same line as the condition is strictly prohibited.'''</span>
 +
 
 +
Example:
 +
<source lang="cpp">
 +
if (foobar < 3) foobar = 45;      // Bad
 +
(foobar < 3 && (foobar = 45));    // Bad
 +
</source>
 +
 
 +
Violating this rule will result in '''instant rejection'''.
 +
 
 +
Examples of good if statement wordings:
 +
<source lang="cpp">
 +
if (foobar < 3)
 +
foobar = 45;
 +
 
 +
if (foobar < 6) {
 +
foobar = 62;
 +
return;
 +
}
 +
</source>
 +
 
 +
==== Nested for loop exception ====
 +
Special exception to the standard bracing/indent rules for nested loops:
 +
If a nested loop iterates over a set of coordinates, it is permitted to omit the braces for all but the innermost loop and keep the outer loops at the same indentation level, like so:
 +
<source lang="cpp">
 +
for (s16 z = pmin.Z; z <= pmax.Z, z++)
 +
for (s16 y = pmin.Y; y <= pmax.Y; y++)
 +
for (s16 x = pmin.X; x <= pmax.X; x++) {
 +
// ... do stuff here ...
 +
}
 +
</source>
 +
 
 +
=== C++ features ===
 +
 
 +
'''Don't''':
 +
* Avoid passing non-<code>const</code> references to functions.
 
* Don't use initializer lists unless absolutely necessary (initializing an object inside a class, or initializing a reference).
 
* Don't use initializer lists unless absolutely necessary (initializing an object inside a class, or initializing a reference).
 +
* Try to minimize the use of exceptions.
 
* Avoid operator overloading like the plague.
 
* Avoid operator overloading like the plague.
* Don't use iterators when unnecessary.
+
** Exceptions to this rule are <code>operator==</code> and <code>operator!=</code> which make sense to define for custom types.
* Avoid templates unless they are very convenient.
+
* Templates are okay if their convenience justifies it. But don't turn the code into a template maze.
* Usage of macros is not discouraged at all, [http://cgit.freedesktop.org/xorg/xserver/tree/randr/rrscreen.c#n325 just don't overdo it like X.org].
+
* Usage of macros is not discouraged, just don't overdo it [http://cgit.freedesktop.org/xorg/xserver/tree/randr/rrscreen.c?id=01e18af17f8dc91451fbd0902049045afd1cea7e#n325 like X.org]. It's better to use inline functions or lambdas instead.
 +
* Don't use distracting and unnecessary amounts of object-oriented abstraction.
 +
** Don't add unnecessary design patterns to your code, such as factories/providers/sources.
 +
** This also applies to interfaces. If there is exactly one implementor you probably don't need one.
 +
 
 +
'''Do''':
 +
* Consider <code>std::unique_ptr&lt;T&gt;</code> over bare pointers whenever possible.
 +
** <code>std::shared_ptr&lt;T&gt;</code> is only used when there isn't an obvious class that can own the data.
 +
* Use <code>auto</code> in variable declarations when appropriate.
 +
** Generally this applies to long, complicated or templated type names and in all for-iterator loops.
 +
* Embrace const correctness.
 +
* Similarly, prefer <code>std::string_view</code> over <code>const std::string &</code>.
 +
* Do not use const references with the Irrlicht vector types (<code>v3f</code>, <code>v3s16</code> et al). Transferring these by value is generally more efficient and in many cases the vectors themselves are smaller than a pointer (8 bytes on 64-bit platforms).
 +
 
 
=== Classes ===
 
=== Classes ===
* Don't put actual code in header files, unless it's a 3-liner or an inline function.
+
 
 +
* '''Class names are ''PascalCase'', method names are ''camelCase''.'''
 +
* Don't put actual code in header files, unless it's a 4-liner, an inline function, or part of a template.
 
* Class definitions should go in header files.
 
* Class definitions should go in header files.
* Substantial (over 4 lines) methods are defined outside of the class definition.
+
* Substantial methods (over 4 lines) should be defined outside of the class definition.
* Class names are PascalCase, method names are camelCase.
+
* Functions not part of any class should use <code>lowercase_underscore_style()</code>.
* Functions not part of any class should be <code>unix_lowercase_underscore_style()</code>.
+
 
 
=== Comments ===
 
=== Comments ===
 +
 +
* Doxygen comments are acceptable, but '''please''' put them in the header file.
 
* Don't make uninformative comments like this:
 
* Don't make uninformative comments like this:
/*
+
 
Draw "Loading" screen
+
<source lang="cpp">
*/
+
// Draw "Loading" screen
+
draw_load_screen(L"Loading...", driver, font);
draw_load_screen(L"Loading...", driver, font);
+
</source>
 +
 
 
* Add comments to explain a non-trivial but important detail about the code, or explain behavior that is not obvious.
 
* Add comments to explain a non-trivial but important detail about the code, or explain behavior that is not obvious.
=== Use STL, avoid Irrlicht containers, and no, Boost will not even be considered, so forget it. ===
+
* For comments with text, be sure to add a space between the text and the comment tokens:
 +
 
 +
<source lang="cpp">
 +
DoThingHere();  // This does thing    <--- yes!
 +
DoThingHere();  /* This does thing */ <--- yes!
 +
 
 +
DoThingHere();  //This does thing      <--- no!
 +
DoThingHere();  /*This does thing*/    <--- no!
 +
DoThingHere();//This does thing        <--- no!
 +
</source>
 +
 
 +
=== Use STL, avoid Irrlicht containers, and no, Boost will not even be considered, so forget it ===
 +
 
 +
* In general, adding new dependencies is considered serious business.
 +
* Boost will never be an option.
 +
 
 
=== Don't let things get too large ===
 
=== Don't let things get too large ===
* Try to keep lines under 80 characters. It's okay if it goes over by a few, but 90 character lines or larger are definitely unacceptable.
+
 
* Functions should not have over 200 lines of code - if you are concerned with having to pass too many parameters to child functions, make whatever it is into a class.
+
* '''Try to keep lines under 95 characters.''' It's okay if it goes over by a few, but do not exaggerate. (Note that this column count assumes 4-space indents.)
* Don't let files get too large (over 1500 lines of code).
+
* Functions should not have over 200 lines of code if you are concerned with having to pass too many parameters to child functions, make whatever it is into a class.
* Currently existing huge files (game.cpp, server.cpp, etc.) are in the slow process of being cleaned up.
+
* Don't let files get too large (over 1500 lines of code). Currently, existing huge files (<code>game.cpp</code>, <code>server.cpp</code>, ) are in the slow process of being cleaned up.
 +
 
 +
=== Files ===
 +
 
 +
* Files should be named using ''snake_case'' style.
 +
* Files should have includes for everything that they depend on. Don't depend on, eg, <code>"util/numeric.h"</code> including <code><string></code>!
 +
* Uniqueness when compiling headers is ensured by using <code>#pragma once</code>. ([https://github.com/minetest/minetest/issues/6259 Accepted by all coredevs])
 +
 
 +
<source lang="cpp">
 +
#pragma once
 +
 
 +
#include <string>
 +
 
 +
class Foo {
 +
};
 +
 
 +
</source>
 +
 
 +
* All files should include the appropriate license header.
 +
 
 
=== Miscellaneous ===
 
=== Miscellaneous ===
* <span style="color: red"><big>DO NOT USE OR, USE ||.  Code that uses 'or' instead of '||' will be INSTANTLY rejected.</big></span>
+
 
* Set pointer values to NULL, not 0. Contrary to what some people may believe, NULL is a part of the official C++ standard.
+
* <span style="color: red">Do '''not''' use <code>or</code>, use <code>||</code>.</span>
* Use of Hungarian notation is very limited, to g_ for globals (rare in the first place) and m_ for members. The latter is discouraged for newer code (since one can simply notice there is no variable by that name declared in that method's scope), but needed when adding a member to older code for consistency.
+
* Set pointer values to <code>nullptr</code> (C++11), not 0 or <code>NULL</code>.
* Don't use distracting and unnecessary amounts of object orientated abstraction. See [https://github.com/MovingBlocks/Terasology Terasology] and [https://github.com/prestidigitator/minetest/blob/objnoise/src/noise.h a certain enterprisey Java coder's conception of perlin noise] as examples of what *not* to do.
+
* When using float literals, add the <code>f</code> suffix, e.g. <code>float k = 0.0f;</code> and not <code>float k = 0.0;</code>.
 +
* Avoid non-ASCII characters in source files. Other UTF-8 characters may (only) be used in string literals and comments where ASCII would worsen readability.
 +
* Use of Hungarian notation is very limited. Scope specifiers such as <code>g_</code> for globals, <code>s_</code> for statics, or <code>m_</code> for members are allowed. The prefix <code>m_</code> is discouraged for public members in newer code as it is a part of the class interface, but sometimes needed for consistency when adding a member to older code.
 +
* Use ''snake_case'' for local variables, not ''camelCase''.
 +
* In <code>switch-case</code> statements, add <code>break</code> to the last case and to the <code>default</code> case.
 +
* In <code>if-else</code> statements, put the code which is more likely to be executed first.
 +
 
 +
[[Category:Core Engine]]
 +
[[Category:Rules and Guidelines]]

Latest revision as of 21:04, 6 March 2024

This is the coding style used for C/C++ code. Also see the Lua code style guidelines.

The coding style is based on the Linux kernel code style. Much of the existing code doesn't follow the current code style guidelines, do not try to replicate that. Use your best judgment for C++-specific syntax.

Currently, the code uses C++17. Do not use features that depend on more recent versions.

Spelling

Use American English, but avoid idioms that may be difficult to understand by non-native speakers.

Function declarations

In case your function parameters don't fit within the defined line length, use the following style. Indention for continuation lines is exactly two tabs.

void some_function_name(type1 param1, type2 param2, type3 param3,
		type4 param4, type5 param5, type6 param6, type7 param7)
{
	...
}

Sometimes with complex function declarations, it might be messy to define as many parameters as possible on the same line. This is acceptable too (and currently used in some places):

void some_function_name(
		const ReallyBigLongTypeName &param1,
		ReallyBigLongTypeName *param2,
		void *param3,
		size_t param4,
		const void *param5,
		size_t param6)
{
	...
}

No more than 7 parameters allowed (except for constructors).

Spaces

  • Do not use spaces to indent.
  • Try to stay under 6 levels of indentation.
  • Add spaces between operators so they line up when appropriate (don't go overboard). For example:
np_terrain_base   = settings->getNoiseParams("mgv6_np_terrain_base");
np_terrain_higher = settings->getNoiseParams("mgv6_np_terrain_higher");
np_steepness      = settings->getNoiseParams("mgv6_np_steepness");
np_height_select  = settings->getNoiseParams("mgv6_np_height_select");
...
bool success =
		np_terrain_base  && np_terrain_higher && np_steepness &&
		np_height_select && np_trees          && np_mud       &&
		np_beach         && np_biome          && np_cave;

The above code looks really nice.

  • Separate different parts of functions with newlines for readability.
  • Separate functions by two newlines (not necessary, but encouraged).
  • Use a space after if, else, for, do, while, switch, case, try, catch, etc.
  • When breaking conditionals, indent following lines of the conditional with two tabs and the statement body with one tab. For example:
for (std::vector<std::string>::iterator it = strings.begin();
		it != strings.end();
		++it) {
	*it = it->substr(1, 1);
}
  • Align backslashes for multi-line macros with spaces:
#define FOOBAR(x) do {    \
	int __temp = (x); \
	foo(__temp);      \
} while (0)

Bracing and indentation

if statements

This rule has already been explicitly stated in the Linux kernel code style from which this code style inherits, but it will be repeated here:

Putting the body of an if statement on the same line as the condition is strictly prohibited.

Example:

if (foobar < 3) foobar = 45;      // Bad 
(foobar < 3 && (foobar = 45));    // Bad

Violating this rule will result in instant rejection.

Examples of good if statement wordings:

if (foobar < 3)
	foobar = 45;

if (foobar < 6) {
	foobar = 62;
	return;
}

Nested for loop exception

Special exception to the standard bracing/indent rules for nested loops: If a nested loop iterates over a set of coordinates, it is permitted to omit the braces for all but the innermost loop and keep the outer loops at the same indentation level, like so:

for (s16 z = pmin.Z; z <= pmax.Z, z++)
for (s16 y = pmin.Y; y <= pmax.Y; y++)
for (s16 x = pmin.X; x <= pmax.X; x++) {
	// ... do stuff here ...
}

C++ features

Don't:

  • Avoid passing non-const references to functions.
  • Don't use initializer lists unless absolutely necessary (initializing an object inside a class, or initializing a reference).
  • Try to minimize the use of exceptions.
  • Avoid operator overloading like the plague.
    • Exceptions to this rule are operator== and operator!= which make sense to define for custom types.
  • Templates are okay if their convenience justifies it. But don't turn the code into a template maze.
  • Usage of macros is not discouraged, just don't overdo it like X.org. It's better to use inline functions or lambdas instead.
  • Don't use distracting and unnecessary amounts of object-oriented abstraction.
    • Don't add unnecessary design patterns to your code, such as factories/providers/sources.
    • This also applies to interfaces. If there is exactly one implementor you probably don't need one.

Do:

  • Consider std::unique_ptr<T> over bare pointers whenever possible.
    • std::shared_ptr<T> is only used when there isn't an obvious class that can own the data.
  • Use auto in variable declarations when appropriate.
    • Generally this applies to long, complicated or templated type names and in all for-iterator loops.
  • Embrace const correctness.
  • Similarly, prefer std::string_view over const std::string &.
  • Do not use const references with the Irrlicht vector types (v3f, v3s16 et al). Transferring these by value is generally more efficient and in many cases the vectors themselves are smaller than a pointer (8 bytes on 64-bit platforms).

Classes

  • Class names are PascalCase, method names are camelCase.
  • Don't put actual code in header files, unless it's a 4-liner, an inline function, or part of a template.
  • Class definitions should go in header files.
  • Substantial methods (over 4 lines) should be defined outside of the class definition.
  • Functions not part of any class should use lowercase_underscore_style().

Comments

  • Doxygen comments are acceptable, but please put them in the header file.
  • Don't make uninformative comments like this:
// Draw "Loading" screen
draw_load_screen(L"Loading...", driver, font);
  • Add comments to explain a non-trivial but important detail about the code, or explain behavior that is not obvious.
  • For comments with text, be sure to add a space between the text and the comment tokens:
DoThingHere();  // This does thing    <--- yes!
DoThingHere();  /* This does thing */ <--- yes!

DoThingHere();  //This does thing      <--- no!
DoThingHere();  /*This does thing*/    <--- no!
DoThingHere();//This does thing        <--- no!

Use STL, avoid Irrlicht containers, and no, Boost will not even be considered, so forget it

  • In general, adding new dependencies is considered serious business.
  • Boost will never be an option.

Don't let things get too large

  • Try to keep lines under 95 characters. It's okay if it goes over by a few, but do not exaggerate. (Note that this column count assumes 4-space indents.)
  • Functions should not have over 200 lines of code – if you are concerned with having to pass too many parameters to child functions, make whatever it is into a class.
  • Don't let files get too large (over 1500 lines of code). Currently, existing huge files (game.cpp, server.cpp, …) are in the slow process of being cleaned up.

Files

  • Files should be named using snake_case style.
  • Files should have includes for everything that they depend on. Don't depend on, eg, "util/numeric.h" including <string>!
  • Uniqueness when compiling headers is ensured by using #pragma once. (Accepted by all coredevs)
#pragma once

#include <string>

class Foo {
};
  • All files should include the appropriate license header.

Miscellaneous

  • Do not use or, use ||.
  • Set pointer values to nullptr (C++11), not 0 or NULL.
  • When using float literals, add the f suffix, e.g. float k = 0.0f; and not float k = 0.0;.
  • Avoid non-ASCII characters in source files. Other UTF-8 characters may (only) be used in string literals and comments where ASCII would worsen readability.
  • Use of Hungarian notation is very limited. Scope specifiers such as g_ for globals, s_ for statics, or m_ for members are allowed. The prefix m_ is discouraged for public members in newer code as it is a part of the class interface, but sometimes needed for consistency when adding a member to older code.
  • Use snake_case for local variables, not camelCase.
  • In switch-case statements, add break to the last case and to the default case.
  • In if-else statements, put the code which is more likely to be executed first.