Code Formatting Conventions

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Revision as of 00:48, 5 December 2015 by DrMcCoy (Talk | contribs) (Add section "Include order")

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Note: These are mostly the ScummVM code formatting conventions, with some minor changes.

Use common sense

These are conventions which we try to follow when writing code for xoreos. Sticking to a common set of formatting / indention rules makes it easier to read through our source base (which now exceed half a million lines of code by far, making this quite important). If you want to submit patches, please try to adhere to these rules.

We don't always follow these rules slavishly, in certain cases it is OK (and in fact might be favorable) to stray from them. Applying common sense, as usual, is a good idea.

In the following examples tabs are replaced by spaces for visual consistency with the Code Formatting Conventions. But in actual code, use tabs for indentations (our tabs are assumed to be 4 spaces wide).

C++ Standard

We mainly follow the C++03 standard, but we also use C99-style known-width integer type. See src/common/types.h for details.

Apart from that, we like to keep the standard as low as possible, for compatibility reasons. If there's a compelling reason, you can of course use C++11 features. But please do so only if you absolutely have to; if the rest of the codebase does something the old-fashioned way, it's best to keep doing it that way. For example, don't introduce auto variables just for the sake of an iterator for-loop.

Hugging braces

Braces in your code should look like the following example:

for (int i = 0; i < t; i++) {

if (j < k) {
} else if (j > k) {
} else {

class Dummy {

Did you see the {}'s on that?

Tabs for indenting, spaces for alignment

Says it all, really.


Conventional operators surrounded by a space character

a = (b + c) * d;

C++ reserved words separated from opening parentheses by a white space

while (true) {

Commas followed by a white space

someFunction(a, b, c);
int d, e;

Semicolons followed by a space character, if there is more on a line

for (int a = 0; b < c; d++)
doSomething(e); doSomething(f);	// This is probably bad style anyway

Semicolons preceded by a space character, if it ends an empty loop body

It should also contain a comment to make it clear that the loop is intentionally empty.

while (i < length - 1 && array[++i] != item) ; // Look for index of item with an empty loop

The following syntax is also acceptable:

while (i < length - 1 && array[++i] != item)
	; //this loop is intentionally empty

When declaring class inheritance and in a ? construct, colons should be surrounded by white space

class BusWheel : public RubberInflatable {
(isNight) ? colorMeDark() : colorMeBright();

Indentation level is not increased after namespace clause

namespace Scumm {

byte Actor::kInvalidBox = 0;

void Actor::initActorClass(ScummEngine *scumm) {
    _vm = scumm;

} // End of namespace Scumm

However, namespaces used solely for forward-declarations should indent

namespace Aurora {
    namespace NWScript {
        class Object;

Array delete operator has no whitespace before []

delete[] foo;

Template definitions

No whitespace between template keyword and <

template<typename foo>
void myFunc(foo arg) {
    // ...

Operator overloading

Operator keyword is NOT separated from the name, except for type conversion operators where it is required.

struct Foo {
    void operator()() {
        // ...

    operator bool() {
        return true;

Pointers and casts

One whitespace after a cast.

const char *ptr = (const char *) foobar;


We use the same rule for references as we do for pointers: use a whitespace before the "&" but not after it.

int i = 0;
int &ref = i;

Trailing whitespace

No trailing whitespace, at all. This means that lines should never end with spaces or tabs. Remove them. Empty lines should be completely empty; not even indenting tabs should be there.

Include order

Include directives should be grouped by subsystem, roughly ordered by specificity, from general to specific.

The group order is as follows:

  • C++ versions of standard C headers
  • Standard C++ headers
  • Standard C headers
  • Library includes
  • src/common
  • src/aurora
  • src/graphics
  • src/sound
  • src/video
  • src/events
  • src/engines

Each group is separated by an empty line. The includes within each group are again ordered roughly by specificity, with includes used by other includes first. But in a .cpp file implementing an interface specified in a .h file, the .h file sits ontop of its group.

For example, these could be the include directives in src/engines/nwn/game.cpp:

#include <cassert>

#include <list>
#include <map>

#include "src/common/util.h"
#include "src/common/ustring.h"
#include "src/common/filelist.h"

#include "src/aurora/types.h"
#include "src/aurora/talkman.h"

#include "src/engines/aurora/util.h"

#include "src/engines/nwn/game.h"
#include "src/engines/nwn/util.h"
#include "src/engines/nwn/nwn.h"

Switch/Case constructs

switch (cmd) {
    case kSomeCmd:
        // Fall Through intended
    case kSomeVerySimilarCmd:
    case kSaveCmd:
    case kLoadCmd:
    case kPlayCmd:
        Dialog::handleCommand(sender, cmd, data);
  • Note comment on whether fall through is intentional.



Basically, you have two choices (this has historical reasons, and we probably should try to unify this one day):

  1. Camel case with prefix 'k':
  2. All upper case, with words separated by underscores (no leading/trailing underscores):

(As a side remark, we recommend avoiding #define for creating constants, because these can lead to weird and difficult to track down conflicts. Instead use enums or the const keyword.)

Type names

Camel case starting with upper case.

class MyClass { /* ... */ };
struct MyStruct { /* ... */ };
typedef int MyInt;

Class member variables

Prefixed with '_' and in camel case (Yo! no underscore separators), starting with lowercase.

char *_someVariableName;

Class methods

Camel case, starting with lowercase.

void thisIsMyFancyMethod();

Local variables

Use camel case (Yo! no underscore separators), starting with lowercase.

char *someVariableName;

Note that for POD structures it is fine to use this rule too.

Global variables

In general you should avoid global variables, but if it can't be avoided, use 'g_' as prefix, camel case, and start with lowercase

int g_someGlobalVariable;

Special comments

Special Keywords

The following goes slightly beyond code formatting: We use certain keywords (together with an explanatory text) to mark certain sections of our code. In particular:

  • FIXME marks code that contains hacks or bad temporary workarounds, things that really should be revised at a later point.
  • TODO marks incomplete code, or things that could be done better but are left for the future.
  • WORKAROUND marks code that works around bugs in the original game, like script bugs. Sometimes these bugs worked in the original due to bugs in the original engine, sometimes the bug was visible in the original, too. It's important that you explain here what exactly you work around, and if applicable, refer to relevant tracker items!

Doxygen documentation comments

xoreos uses the Doxygen software to generate HTML documentation for the codebase.

Doxygen supports documentation blocks. These are specially-formatted comments that doxygen prints out in the generated documentation. They are similar in purpose to Java's JavaDoc or Python's docstrings.

There are many ways to mark such comments, but developers are encouraged to use the JavaDoc style:

/** Move ("warp") the mouse cursor to the specified position in virtual
 *  screen coordinates.
 *  @param x   the new x position of the mouse.
 *  @param y   the new y position of the mouse.
virtual void warpMouse(int x, int y) = 0;

As shown in the example, documentation blocks also support several special commands such as param. Those are prefixed with either @ or \, but developers should always use @.

If you want to add a brief explanation of a variable or function after its declaration, this is the correct syntax:

int16 x;	///< The horizontal part of the point.
int16 y;	///< The vertical part of the point.

For more information, visit the official documentation:

Automatically converting code to our conventions

The following settings for Artistic Style (also known as astyle) approximate our code formatting conventions and can be used to quickly convert a big bunch of source files to our conventions. Note that you may still have to manually clean up some stuff afterwards.


Alternatively, this config file for uncrustify should also work as a starting point for our conventions. Again, you may still clean things up manually.