ClangFormat¶

ClangFormat describes a set of tools that are built on top of LibFormat. It can support your workflow in a variety of ways including a standalone tool and editor integrations.

Standalone Tool¶

clang-format is located in clang/tools/clang-format and can be used to format C/C++/Java/JavaScript/Objective-C/Protobuf/C# code.

$ clang-format -help
OVERVIEW: A tool to format C/C++/Java/JavaScript/Objective-C/Protobuf/C# code.

If no arguments are specified, it formats the code from standard input
and writes the result to the standard output.
If <file>s are given, it reformats the files. If -i is specified
together with <file>s, the files are edited in-place. Otherwise, the
result is written to the standard output.

USAGE: clang-format [options] [<file> ...]

OPTIONS:

Clang-format options:

  -assume-filename=<string> - When reading from stdin, clang-format assumes this
                              filename to look for a style config file (with
                              -style=file) and to determine the language.
  -cursor=<uint>            - The position of the cursor when invoking
                              clang-format from an editor integration
  -dump-config              - Dump configuration options to stdout and exit.
                              Can be used with -style option.
  -fallback-style=<string>  - The name of the predefined style used as a
                              fallback in case clang-format is invoked with
                              -style=file, but can not find the .clang-format
                              file to use.
                              Use -fallback-style=none to skip formatting.
  -i                        - Inplace edit <file>s, if specified.
  -length=<uint>            - Format a range of this length (in bytes).
                              Multiple ranges can be formatted by specifying
                              several -offset and -length pairs.
                              When only a single -offset is specified without
                              -length, clang-format will format up to the end
                              of the file.
                              Can only be used with one input file.
  -lines=<string>           - <start line>:<end line> - format a range of
                              lines (both 1-based).
                              Multiple ranges can be formatted by specifying
                              several -lines arguments.
                              Can't be used with -offset and -length.
                              Can only be used with one input file.
  -offset=<uint>            - Format a range starting at this byte offset.
                              Multiple ranges can be formatted by specifying
                              several -offset and -length pairs.
                              Can only be used with one input file.
  -output-replacements-xml  - Output replacements as XML.
  -sort-includes            - Sort touched include lines
  -style=<string>           - Coding style, currently supports:
                                LLVM, Google, Chromium, Mozilla, WebKit.
                              Use -style=file to load style configuration from
                              .clang-format file located in one of the parent
                              directories of the source file (or current
                              directory for stdin).
                              Use -style="{key: value, ...}" to set specific
                              parameters, e.g.:
                                -style="{BasedOnStyle: llvm, IndentWidth: 8}"
  -verbose                  - If set, shows the list of processed files

Generic Options:

  -help                     - Display available options (-help-hidden for more)
  -help-list                - Display list of available options (-help-list-hidden for more)
  -version                  - Display the version of this program

When the desired code formatting style is different from the available options, the style can be customized using the -style="{key: value, ...}" option or by putting your style configuration in the .clang-format or _clang-format file in your project’s directory and using clang-format -style=file.

An easy way to create the .clang-format file is:

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

Available style options are described in Clang-Format Style Options.

Vim Integration¶

There is an integration for vim which lets you run the clang-format standalone tool on your current buffer, optionally selecting regions to reformat. The integration has the form of a python-file which can be found under clang/tools/clang-format/clang-format.py.

This can be integrated by adding the following to your .vimrc:

map <C-K> :pyf <path-to-this-file>/clang-format.py<cr>
imap <C-K> <c-o>:pyf <path-to-this-file>/clang-format.py<cr>

The first line enables clang-format for NORMAL and VISUAL mode, the second line adds support for INSERT mode. Change “C-K” to another binding if you need clang-format on a different key (C-K stands for Ctrl+k).

With this integration you can press the bound key and clang-format will format the current line in NORMAL and INSERT mode or the selected region in VISUAL mode. The line or region is extended to the next bigger syntactic entity.

It operates on the current, potentially unsaved buffer and does not create or save any files. To revert a formatting, just undo.

An alternative option is to format changes when saving a file and thus to have a zero-effort integration into the coding workflow. To do this, add this to your .vimrc:

function! Formatonsave()
  let l:formatdiff = 1
  pyf ~/llvm/tools/clang/tools/clang-format/clang-format.py
endfunction
autocmd BufWritePre *.h,*.cc,*.cpp call Formatonsave()

Emacs Integration¶

Similar to the integration for vim, there is an integration for emacs. It can be found at clang/tools/clang-format/clang-format.el and used by adding this to your .emacs:

(load "<path-to-clang>/tools/clang-format/clang-format.el")
(global-set-key [C-M-tab] 'clang-format-region)

This binds the function clang-format-region to C-M-tab, which then formats the current line or selected region.

BBEdit Integration¶

clang-format cannot be used as a text filter with BBEdit, but works well via a script. The AppleScript to do this integration can be found at clang/tools/clang-format/clang-format-bbedit.applescript; place a copy in ~/Library/Application Support/BBEdit/Scripts, and edit the path within it to point to your local copy of clang-format.

With this integration you can select the script from the Script menu and clang-format will format the selection. Note that you can rename the menu item by renaming the script, and can assign the menu item a keyboard shortcut in the BBEdit preferences, under Menus & Shortcuts.

CLion Integration¶

clang-format is integrated into CLion as an alternative code formatter. It is disabled by default and can be turned on in Settings/Preferences | Editor | Code Style.

If clang-format support is enabled, CLion detects config files when opening a project and suggests overriding the current IDE settings. Code style rules from the .clang-format files are then applied automatically to all editor actions, including auto-completion, code generation, and refactorings.

Visual Studio Integration¶

Download the latest Visual Studio extension from the alpha build site. The default key-binding is Ctrl-R,Ctrl-F.

Script for patch reformatting¶

The python script clang/tools/clang-format/clang-format-diff.py parses the output of a unified diff and reformats all contained lines with clang-format.

usage: clang-format-diff.py [-h] [-i] [-p NUM] [-regex PATTERN] [-style STYLE]

Reformat changed lines in diff. Without -i option just output the diff that
would be introduced.

optional arguments:
  -h, --help      show this help message and exit
  -i              apply edits to files instead of displaying a diff
  -p NUM          strip the smallest prefix containing P slashes
  -regex PATTERN  custom pattern selecting file paths to reformat
  -style STYLE    formatting style to apply (LLVM, Google, Chromium, Mozilla,
                  WebKit)

So to reformat all the lines in the latest git commit, just do:

git diff -U0 --no-color HEAD^ | clang-format-diff.py -i -p1

With Mercurial/hg:

hg diff -U0 --color=never | clang-format-diff.py -i -p1

In an SVN client, you can do:

svn diff --diff-cmd=diff -x -U0 | clang-format-diff.py -i

The option -U0 will create a diff without context lines (the script would format those as well).