Configuring Style with clang-format¶

clang-format supports two ways to provide custom style options: directly specify style configuration in the -style= command line option or use -style=file and put style configuration in the .clang-format or _clang-format file in the project directory.

When using -style=file, clang-format for each input file will try to find the .clang-format file located in the closest parent directory of the input file. When the standard input is used, the search is started from the current directory.

The .clang-format file uses YAML format:

key1: value1
key2: value2
# A comment.
...

The configuration file can consist of several sections each having different Language: parameter denoting the programming language this section of the configuration is targeted at. See the description of the Language option below for the list of supported languages. The first section may have no language set, it will set the default style options for all lanugages. Configuration sections for specific language will override options set in the default section.

When clang-format formats a file, it auto-detects the language using the file name. When formatting standard input or a file that doesn’t have the extension corresponding to its language, -assume-filename= option can be used to override the file name clang-format uses to detect the language.

An example of a configuration file for multiple languages:

---
# We'll use defaults from the LLVM style, but with 4 columns indentation.
BasedOnStyle: LLVM
IndentWidth: 4
---
Language: Cpp
# Force pointers to the type for C++.
DerivePointerAlignment: false
PointerAlignment: Left
---
Language: JavaScript
# Use 100 columns for JS.
ColumnLimit: 100
---
Language: Proto
# Don't format .proto files.
DisableFormat: true
...

An easy way to get a valid .clang-format file containing all configuration options of a certain predefined style is:

clang-format -style=llvm -dump-config > .clang-format

When specifying configuration in the -style= option, the same configuration is applied for all input files. The format of the configuration is:

-style='{key1: value1, key2: value2, ...}'

Disabling Formatting on a Piece of Code¶

Clang-format understands also special comments that switch formatting in a delimited range. The code between a comment // clang-format off or /* clang-format off */ up to a comment // clang-format on or /* clang-format on */ will not be formatted. The comments themselves will be formatted (aligned) normally.

int formatted_code;
// clang-format off
    void    unformatted_code  ;
// clang-format on
void formatted_code_again;

Configuring Style in Code¶

When using clang::format::reformat(...) functions, the format is specified by supplying the clang::format::FormatStyle structure.

Configurable Format Style Options¶

This section lists the supported style options. Value type is specified for each option. For enumeration types possible values are specified both as a C++ enumeration member (with a prefix, e.g. LS_Auto), and as a value usable in the configuration (without a prefix: Auto).

BasedOnStyle (string)

The style used for all options not specifically set in the configuration.

This option is supported only in the clang-format configuration (both within -style='{...}' and the .clang-format file).

Possible values:

• LLVM A style complying with the LLVM coding standards
• Google A style complying with Google’s C++ style guide
• Chromium A style complying with Chromium’s style guide
• Mozilla A style complying with Mozilla’s style guide
• WebKit A style complying with WebKit’s style guide

AccessModifierOffset (int)

The extra indent or outdent of access modifiers, e.g. public:.

AlignAfterOpenBracket (BracketAlignmentStyle)

If true, horizontally aligns arguments after an open bracket.

This applies to round brackets (parentheses), angle brackets and square brackets. This will result in formattings like

Possible values:

• BAS_Align (in configuration: Align) Align parameters on the open bracket, e.g.:

  someLongFunction(argument1,
                   argument2);
  

• BAS_DontAlign (in configuration: DontAlign) Don’t align, instead use ContinuationIndentWidth, e.g.:

  someLongFunction(argument1,
      argument2);
  

• BAS_AlwaysBreak (in configuration: AlwaysBreak) Always break after an open bracket, if the parameters don’t fit on a single line, e.g.:

  someLongFunction(
      argument1, argument2);
  

AlignConsecutiveAssignments (bool)

If true, aligns consecutive assignments.

This will align the assignment operators of consecutive lines. This will result in formattings like

int aaaa = 12;
int b    = 23;
int ccc  = 23;

AlignConsecutiveDeclarations (bool)

If true, aligns consecutive declarations.

This will align the declaration names of consecutive lines. This will result in formattings like

int         aaaa = 12;
float       b = 23;
std::string ccc = 23;

AlignEscapedNewlinesLeft (bool)

If true, aligns escaped newlines as far left as possible. Otherwise puts them into the right-most column.

AlignOperands (bool)

If true, horizontally align operands of binary and ternary expressions.

AlignTrailingComments (bool)

If true, aligns trailing comments.

AllowAllParametersOfDeclarationOnNextLine (bool)

Allow putting all parameters of a function declaration onto the next line even if BinPackParameters is false.

AllowShortBlocksOnASingleLine (bool)

Allows contracting simple braced statements to a single line.

E.g., this allows if (a) { return; } to be put on a single line.

AllowShortCaseLabelsOnASingleLine (bool)

If true, short case labels will be contracted to a single line.

AllowShortFunctionsOnASingleLine (ShortFunctionStyle)

Dependent on the value, int f() { return 0; } can be put on a single line.

Possible values:

• SFS_None (in configuration: None) Never merge functions into a single line.
• SFS_Empty (in configuration: Empty) Only merge empty functions.
• SFS_Inline (in configuration: Inline) Only merge functions defined inside a class. Implies “empty”.
• SFS_All (in configuration: All) Merge all functions fitting on a single line.

AllowShortIfStatementsOnASingleLine (bool)

If true, if (a) return; can be put on a single line.

AllowShortLoopsOnASingleLine (bool)

If true, while (true) continue; can be put on a single line.

AlwaysBreakAfterDefinitionReturnType (DefinitionReturnTypeBreakingStyle)

The function definition return type breaking style to use. This option is deprecated and is retained for backwards compatibility.

Possible values:

• DRTBS_None (in configuration: None) Break after return type automatically. PenaltyReturnTypeOnItsOwnLine is taken into account.
• DRTBS_All (in configuration: All) Always break after the return type.
• DRTBS_TopLevel (in configuration: TopLevel) Always break after the return types of top-level functions.

AlwaysBreakAfterReturnType (ReturnTypeBreakingStyle)

The function declaration return type breaking style to use.

Possible values:

• RTBS_None (in configuration: None) Break after return type automatically. PenaltyReturnTypeOnItsOwnLine is taken into account.
• RTBS_All (in configuration: All) Always break after the return type.
• RTBS_TopLevel (in configuration: TopLevel) Always break after the return types of top-level functions.
• RTBS_AllDefinitions (in configuration: AllDefinitions) Always break after the return type of function definitions.
• RTBS_TopLevelDefinitions (in configuration: TopLevelDefinitions) Always break after the return type of top-level definitions.

AlwaysBreakBeforeMultilineStrings (bool)

If true, always break before multiline string literals.

This flag is mean to make cases where there are multiple multiline strings in a file look more consistent. Thus, it will only take effect if wrapping the string at that point leads to it being indented ContinuationIndentWidth spaces from the start of the line.

AlwaysBreakTemplateDeclarations (bool)

If true, always break after the template<...> of a template declaration.

BinPackArguments (bool)

If false, a function call’s arguments will either be all on the same line or will have one line each.

BinPackParameters (bool)

If false, a function declaration’s or function definition’s parameters will either all be on the same line or will have one line each.

BraceWrapping (BraceWrappingFlags)

Control of individual brace wrapping cases.

If BreakBeforeBraces is set to custom, use this to specify how each individual brace case should be handled. Otherwise, this is ignored.

Nested configuration flags:

• bool AfterClass Wrap class definitions.
• bool AfterControlStatement Wrap control statements (if/for/while/switch/..).
• bool AfterEnum Wrap enum definitions.
• bool AfterFunction Wrap function definitions.
• bool AfterNamespace Wrap namespace definitions.
• bool AfterObjCDeclaration Wrap ObjC definitions (@autoreleasepool, interfaces, ..).
• bool AfterStruct Wrap struct definitions.
• bool AfterUnion Wrap union definitions.
• bool BeforeCatch Wrap before catch.
• bool BeforeElse Wrap before else.
• bool IndentBraces Indent the wrapped braces themselves.

BreakAfterJavaFieldAnnotations (bool)

Break after each annotation on a field in Java files.

BreakBeforeBinaryOperators (BinaryOperatorStyle)

The way to wrap binary operators.

Possible values:

• BOS_None (in configuration: None) Break after operators.
• BOS_NonAssignment (in configuration: NonAssignment) Break before operators that aren’t assignments.
• BOS_All (in configuration: All) Break before operators.

BreakBeforeBraces (BraceBreakingStyle)

The brace breaking style to use.

Possible values:

• BS_Attach (in configuration: Attach) Always attach braces to surrounding context.
• BS_Linux (in configuration: Linux) Like Attach, but break before braces on function, namespace and class definitions.
• BS_Mozilla (in configuration: Mozilla) Like Attach, but break before braces on enum, function, and record definitions.
• BS_Stroustrup (in configuration: Stroustrup) Like Attach, but break before function definitions, ‘catch’, and ‘else’.
• BS_Allman (in configuration: Allman) Always break before braces.
• BS_GNU (in configuration: GNU) Always break before braces and add an extra level of indentation to braces of control statements, not to those of class, function or other definitions.
• BS_WebKit (in configuration: WebKit) Like Attach, but break before functions.
• BS_Custom (in configuration: Custom) Configure each individual brace in BraceWrapping.

BreakBeforeTernaryOperators (bool)

If true, ternary operators will be placed after line breaks.

BreakConstructorInitializersBeforeComma (bool)

Always break constructor initializers before commas and align the commas with the colon.

ColumnLimit (unsigned)

The column limit.

A column limit of 0 means that there is no column limit. In this case, clang-format will respect the input’s line breaking decisions within statements unless they contradict other rules.

CommentPragmas (std::string)

A regular expression that describes comments with special meaning, which should not be split into lines or otherwise changed.

ConstructorInitializerAllOnOneLineOrOnePerLine (bool)

If the constructor initializers don’t fit on a line, put each initializer on its own line.

ConstructorInitializerIndentWidth (unsigned)

The number of characters to use for indentation of constructor initializer lists.

ContinuationIndentWidth (unsigned)

Indent width for line continuations.

Cpp11BracedListStyle (bool)

If true, format braced lists as best suited for C++11 braced lists.

Important differences: - No spaces inside the braced list. - No line break before the closing brace. - Indentation with the continuation indent, not with the block indent.

Fundamentally, C++11 braced lists are formatted exactly like function calls would be formatted in their place. If the braced list follows a name (e.g. a type or variable name), clang-format formats as if the {} were the parentheses of a function call with that name. If there is no name, a zero-length name is assumed.

DerivePointerAlignment (bool)

If true, analyze the formatted file for the most common alignment of & and *. PointerAlignment is then used only as fallback.

DisableFormat (bool)

Disables formatting completely.

ExperimentalAutoDetectBinPacking (bool)

If true, clang-format detects whether function calls and definitions are formatted with one parameter per line.

Each call can be bin-packed, one-per-line or inconclusive. If it is inconclusive, e.g. completely on one line, but a decision needs to be made, clang-format analyzes whether there are other bin-packed cases in the input file and act accordingly.

NOTE: This is an experimental flag, that might go away or be renamed. Do not use this in config files, etc. Use at your own risk.

ForEachMacros (std::vector<std::string>)

A vector of macros that should be interpreted as foreach loops instead of as function calls.

These are expected to be macros of the form:

FOREACH(<variable-declaration>, ...)
  <loop-body>

In the .clang-format configuration file, this can be configured like:

ForEachMacros: ['RANGES_FOR', 'FOREACH']

For example: BOOST_FOREACH.

IncludeCategories (std::vector<IncludeCategory>)

Regular expressions denoting the different #include categories used for ordering #includes.

These regular expressions are matched against the filename of an include (including the <> or “”) in order. The value belonging to the first matching regular expression is assigned and #includes are sorted first according to increasing category number and then alphabetically within each category.

If none of the regular expressions match, UINT_MAX is assigned as category. The main header for a source file automatically gets category 0, so that it is kept at the beginning of the #includes (http://llvm.org/docs/CodingStandards.html#include-style).

To configure this in the .clang-format file, use:

IncludeCategories:
  - Regex:           '^"(llvm|llvm-c|clang|clang-c)/'
    Priority:        2
  - Regex:           '^(<|"(gtest|isl|json)/)'
    Priority:        3
  - Regex:           '.\*'
    Priority:        1

IndentCaseLabels (bool)

Indent case labels one level from the switch statement.

When false, use the same indentation level as for the switch statement. Switch statement body is always indented one level more than case labels.

IndentWidth (unsigned)

The number of columns to use for indentation.

IndentWrappedFunctionNames (bool)

Indent if a function definition or declaration is wrapped after the type.

KeepEmptyLinesAtTheStartOfBlocks (bool)

If true, empty lines at the start of blocks are kept.

Language (LanguageKind)

Language, this format style is targeted at.

Possible values:

• LK_None (in configuration: None) Do not use.
• LK_Cpp (in configuration: Cpp) Should be used for C, C++, ObjectiveC, ObjectiveC++.
• LK_Java (in configuration: Java) Should be used for Java.
• LK_JavaScript (in configuration: JavaScript) Should be used for JavaScript.
• LK_Proto (in configuration: Proto) Should be used for Protocol Buffers (https://developers.google.com/protocol-buffers/).

MacroBlockBegin (std::string)

A regular expression matching macros that start a block.

MacroBlockEnd (std::string)

A regular expression matching macros that end a block.

MaxEmptyLinesToKeep (unsigned)

The maximum number of consecutive empty lines to keep.

NamespaceIndentation (NamespaceIndentationKind)

The indentation used for namespaces.

Possible values:

• NI_None (in configuration: None) Don’t indent in namespaces.
• NI_Inner (in configuration: Inner) Indent only in inner namespaces (nested in other namespaces).
• NI_All (in configuration: All) Indent in all namespaces.

ObjCBlockIndentWidth (unsigned)

The number of characters to use for indentation of ObjC blocks.

ObjCSpaceAfterProperty (bool)

Add a space after @property in Objective-C, i.e. use \@property (readonly) instead of \@property(readonly).

ObjCSpaceBeforeProtocolList (bool)

Add a space in front of an Objective-C protocol list, i.e. use Foo <Protocol> instead of Foo<Protocol>.

PenaltyBreakBeforeFirstCallParameter (unsigned)

The penalty for breaking a function call after “call(”.

PenaltyBreakComment (unsigned)

The penalty for each line break introduced inside a comment.

PenaltyBreakFirstLessLess (unsigned)

The penalty for breaking before the first <<.

PenaltyBreakString (unsigned)

The penalty for each line break introduced inside a string literal.

PenaltyExcessCharacter (unsigned)

The penalty for each character outside of the column limit.

PenaltyReturnTypeOnItsOwnLine (unsigned)

Penalty for putting the return type of a function onto its own line.

PointerAlignment (PointerAlignmentStyle)

Pointer and reference alignment style.

Possible values:

• PAS_Left (in configuration: Left) Align pointer to the left.
• PAS_Right (in configuration: Right) Align pointer to the right.
• PAS_Middle (in configuration: Middle) Align pointer in the middle.

SpaceAfterCStyleCast (bool)

If true, a space may be inserted after C style casts.

SpaceBeforeAssignmentOperators (bool)

If false, spaces will be removed before assignment operators.

SpaceBeforeParens (SpaceBeforeParensOptions)

Defines in which cases to put a space before opening parentheses.

Possible values:

• SBPO_Never (in configuration: Never) Never put a space before opening parentheses.
• SBPO_ControlStatements (in configuration: ControlStatements) Put a space before opening parentheses only after control statement keywords (for/if/while...).
• SBPO_Always (in configuration: Always) Always put a space before opening parentheses, except when it’s prohibited by the syntax rules (in function-like macro definitions) or when determined by other style rules (after unary operators, opening parentheses, etc.)

SpaceInEmptyParentheses (bool)

If true, spaces may be inserted into ‘()’.

SpacesBeforeTrailingComments (unsigned)

The number of spaces before trailing line comments (// - comments).

This does not affect trailing block comments (/**/ - comments) as those commonly have different usage patterns and a number of special cases.

SpacesInAngles (bool)

If true, spaces will be inserted after ‘<’ and before ‘>’ in template argument lists

SpacesInCStyleCastParentheses (bool)

If true, spaces may be inserted into C style casts.

SpacesInContainerLiterals (bool)

If true, spaces are inserted inside container literals (e.g. ObjC and Javascript array and dict literals).

SpacesInParentheses (bool)

If true, spaces will be inserted after ‘(‘ and before ‘)’.

SpacesInSquareBrackets (bool)

If true, spaces will be inserted after ‘[‘ and before ‘]’.

Standard (LanguageStandard)

Format compatible with this standard, e.g. use A<A<int> > instead of A<A<int>> for LS_Cpp03.

Possible values:

• LS_Cpp03 (in configuration: Cpp03) Use C++03-compatible syntax.
• LS_Cpp11 (in configuration: Cpp11) Use features of C++11 (e.g. A<A<int>> instead of A<A<int> >).
• LS_Auto (in configuration: Auto) Automatic detection based on the input.

TabWidth (unsigned)

The number of columns used for tab stops.

UseTab (UseTabStyle)

The way to use tab characters in the resulting file.

Possible values:

• UT_Never (in configuration: Never) Never use tab.
• UT_ForIndentation (in configuration: ForIndentation) Use tabs only for indentation.
• UT_Always (in configuration: Always) Use tabs whenever we need to fill whitespace that spans at least from one tab stop to the next one.

Adding additional style options¶

Each additional style option adds costs to the clang-format project. Some of these costs affect the clang-format developement itself, as we need to make sure that any given combination of options work and that new features don’t break any of the existing options in any way. There are also costs for end users as options become less discoverable and people have to think about and make a decision on options they don’t really care about.

The goal of the clang-format project is more on the side of supporting a limited set of styles really well as opposed to supporting every single style used by a codebase somewhere in the wild. Of course, we do want to support all major projects and thus have established the following bar for adding style options. Each new style option must ..

• be used in a project of significant size (have dozens of contributors)
• have a publicly accessible style guide
• have a person willing to contribute and maintain patches

Examples¶

A style similar to the Linux Kernel style:

BasedOnStyle: LLVM
IndentWidth: 8
UseTab: Always
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false

The result is (imagine that tabs are used for indentation here):

void test()
{
        switch (x) {
        case 0:
        case 1:
                do_something();
                break;
        case 2:
                do_something_else();
                break;
        default:
                break;
        }
        if (condition)
                do_something_completely_different();

        if (x == y) {
                q();
        } else if (x > y) {
                w();
        } else {
                r();
        }
}

A style similar to the default Visual Studio formatting style:

UseTab: Never
IndentWidth: 4
BreakBeforeBraces: Allman
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
ColumnLimit: 0

The result is:

void test()
{
    switch (suffix)
    {
    case 0:
    case 1:
        do_something();
        break;
    case 2:
        do_something_else();
        break;
    default:
        break;
    }
    if (condition)
        do_somthing_completely_different();

    if (x == y)
    {
        q();
    }
    else if (x > y)
    {
        w();
    }
    else
    {
        r();
    }
}