Coding Style

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This article describes general coding style guidelines, which should be used for new ReactOS code. These guidelines apply exclusively to C and C++ source files. The Members of ReactOS agreed on this document in the October 2013 meeting.

As much existing ReactOS code as possible should be converted to this style unless there are reasons against doing this (like if the code is going to be rewritten from scratch in the near future). See Notes on reformatting existing code for more details.

Code synchronized with other sources (like Wine) must not be rewritten. README.WINE, README.FSD and 3rd Party Files.txt files can be used for tracking synchronized files.

File Structure

  1. Every ReactOS source code file should include a file header like this:
    /*
     * PROJECT:     ReactOS Kernel
     * LICENSE:     GPL-2.0-or-later (https://spdx.org/licenses/GPL-2.0-or-later)
     * PURPOSE:     Does cool things like ...
     * COPYRIGHT:   Copyright 2017 Arno Nymous (abc@mailaddress.com)
     *              Copyright 2017 Mike Blablabla (mike@blabla.com)
     */
    

    Please use SPDX license identifiers available at https://spdx.org/licenses. This makes our source file parseable by licensing tools!

    You should add yourself to the COPYRIGHT section of a file if you did a major contribution to it and could take responsibility for the whole file or a part of it.

    FILE line of the old header should be removed.

  2. Use a header comparable to the following one for functions:
    /**
     * @brief Do nothing for 500ms.
     *
     * (optional) Description of what the function does. This part may refer to the parameters
     * of the function, like @p param1 or @p param2. A word of code can also be
     * inserted like @c this which is equivalent to <tt>this</tt> and can be useful
     * to say that the function returns a @c void or an @c int. If you want to have
     * more than one word in typewriter font, then just use @<tt@>.
     * Note the empty line before brief, it's important for splitting brief and detailed descriptions.
     *
     * @param[in] InputParameter
     * Description of the parameter.
     *
     * @param[out] OutputParameter
     * Description of the parameter.
     *
     * @param[in,out] InputOutputParameter
     * Description of the parameter.
     *
     * @param SomeParameter
     * Bleh, bleh :)
     *
     * @return
     * STATUS_SUCCESS in case of success, STATUS_UNSUCCESSFUL
     * otherwise.
     *
     * @see SomeOtherAPI
     *
     * @remarks Must be called at IRQL == DISPATCH_LEVEL
     *
     */
    NTSTATUS
    SomeAPI(UINT32 InputParameter, UINT32 *OutputParameter, UINT32 *InputOutputParameter);
    
    Doxygen documentation generator is used for ReactOS codebase. Consider looking into it's manual for the full list of the commands.
  3. For tagging a function as not implemented, use @unimplemented statement before @brief

Indentation

  1. Indent with 4 spaces, don’t use tabs!
  2. Indent both a case label and the case statement of a switch statement.

    Right:

    switch (Condition)
    {
        case 1:
            DoSomething();
            break;
    }
    

    Wrong:

    switch (Condition)
    {
    case 1:
         DoSomething();
         break;
    }
    

Spacing

  1. Do not use spaces around unary operators.
    Right: i++;
    Wrong: i ++;
  2. Place spaces around binary and ternary operators.
    Right: a = b + c;
    Wrong: a=b+c;
  3. Do not place spaces before comma and semicolon.

    Right:

    for (int i = 0; i < 5; i++)
        DoSomething();
    
    func1(a, b);
    

    Wrong:

    for (int i = 0 ; i < 5 ; i++)
        DoSomething();
    
    func1(a , b) ;
    
  4. Place spaces between control statements and their parentheses.

    Right:

    if (Condition)
        DoSomething();
    

    Wrong:

    if(Condition)
        DoSomething();
    
  5. Do not place spaces between a function and its parentheses, or between a parenthesis and its content.

    Right:

    func(a, b);
    

    Wrong:

    func (a, b);
    func( a, b );
    

Line breaking

  1. Each statement should get its own line.

    Right:

    x++;
    y++;
    
    if (Condition)
        DoSomething();
    

    Wrong:

    x++; y++;
    
    if (Condition) DoSomething();
    

Braces

  1. Always put braces ({ and }) on their own lines.
  2. One-line control clauses may use braces, but this is not a requirement. An exception are one-line control clauses including additional comments.

    Right:

    if (Condition)
        DoSomething();
    
    if (Condition)
    {
        DoSomething();
    }
    
    if (Condition)
    {
        // This is a comment
        DoSomething();
    }
    
    if (Condition)
        DoSomething();
    else
        DoSomethingElse();
    
    if (Condition)
    {
        DoSomething();
    }
    else
    {
        DoSomethingElse();
        YetAnother();
    }
    

    Wrong:

    if (Condition) {
        DoSomething();
    }
    
    if (Condition)
        // This is a comment
        DoSomething();
    
    if (Condition)
        DoSomething();
    else
    {
        DoSomethingElse();
        YetAnother();
    }
    

Control structures

  1. Don’t use inverse logic in control clauses.
    Right: if (i == 1)
    Wrong: if (1 == i)
  2. Avoid too many levels of cascaded control structures. Prefer a “linear style” over a “tree style”. Use goto when it helps to make the code cleaner (e.g. for cleanup paths).

    Right:

    if (!func1())
        return;
    
    i = func2();
    if (i == 0)
        return;
    
    j = func3();
    if (j == 1)
        return;
    
    

    Wrong:

    if (func1())
    {
        i = func2();
        if (func2())
        {
            j = func3();
            if (func3())
            {
                
            }
        }
    }
    

Naming

  1. Capitalize names of variables and functions.
    Hungarian Notation may be used when developing for Win32, but it is not required. If you don’t use it, the first letter of a name must be a capital too (no camelCase). Do not use underscores as separators either.

    Right:

    PLIST_ENTRY FirstEntry;
    VOID NTAPI IopDeleteIoCompletion(PVOID ObjectBody);
    PWSTR pwszTest;
    

    Wrong:

    PLIST_ENTRY first_entry;
    VOID NTAPI iop_delete_io_completion(PVOID objectBody);
    PWSTR pwsztest;
    
  2. Avoid abbreviating function and variable names, use descriptive verbs where possible.
  3. Precede boolean values with meaningful verbs like "is" and "did" if possible and if it fits the usage.

    Right:

    BOOLEAN IsValid;
    BOOLEAN DidSendData;
    

    Wrong:

    BOOLEAN Valid;
    BOOLEAN SentData;
    

Commenting

  1. Avoid line-wasting comments, which could fit into a single line.

    Right:

    // This is a one-line comment
    
    /* This is a C-style comment */
    
    //
    // This is a comment over multiple lines.
    // We don’t define any strict rules for it.
    //
    

    Wrong:

    //
    // This comment wastes two lines
    //
    

Null, false and 0

  1. The null pointer should be written as NULL.
    In the rare case that your environment recommends a different null pointer (e.g. C++11 nullptr), you may use this one of course. Just don’t use the value 0.
  2. Win32/NT Boolean values should be written as TRUE and FALSE.
    In the rare case that you use C/C++ bool variables, you should write them as true and false.
  3. When you need to terminate ANSI or OEM string, or check for its terminator, use ANSI_NULL. If the string is Unicode or Wide string, use UNICODE_NULL.

Notes on reformatting existing code

  • Never totally reformat a file and put a code change into it. Do this in separate commits.
  • If a commit only consists of formatting changes, say this clearly in the commit message by preceding it with [FORMATTING].

Using an automatic code style tool

TO BE ADDED BY User:Zefklop

Points deliberately left out

Additional ideas were suggested during the discussion of this document, but a consensus couldn't be reached on them. Therefore we refrain from enforcing any rules on these points:

See also