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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/JSON/Objective-C/Protobuf/C# code.

$ clang-format --help
OVERVIEW: A tool to format C/C++/Java/JavaScript/JSON/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>] [<file> ...]

OPTIONS:

Clang-format options:

  --Werror                       - If set, changes formatting warnings to errors
  --Wno-error=<value>            - If set don't error out on the specified warning type.
    =unknown                     -   If set, unknown format options are only warned about.
                                     This can be used to enable formatting, even if the
                                     configuration contains unknown (newer) options.
                                     Use with caution, as this might lead to dramatically
                                     differing format depending on an option being
                                     supported or not.
  --assume-filename=<string>     - Set filename used to determine the language and to find
                                   .clang-format file.
                                   Only used when reading from stdin.
                                   If this is not passed, the .clang-format file is searched
                                   relative to the current working directory when reading stdin.
                                   Unrecognized filenames are treated as C++.
                                   supported:
                                     CSharp: .cs
                                     Java: .java
                                     JavaScript: .mjs .js .ts
                                     Json: .json
                                     Objective-C: .m .mm
                                     Proto: .proto .protodevel
                                     TableGen: .td
                                     TextProto: .textpb .pb.txt .textproto .asciipb
                                     Verilog: .sv .svh .v .vh
  --cursor=<uint>                - The position of the cursor when invoking
                                   clang-format from an editor integration
  --dry-run                      - If set, do not actually make the formatting changes
  --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. Defaults to 'LLVM'.
                                   Use -fallback-style=none to skip formatting.
  --ferror-limit=<uint>          - Set the maximum number of clang-format errors to emit
                                   before stopping (0 = no limit).
                                   Used only with --dry-run or -n
  --files=<filename>             - A file containing a list of files to process, one
                                   per line.
  -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.
  -n                             - Alias for --dry-run
  --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.
  --qualifier-alignment=<string> - If set, overrides the qualifier alignment style
                                   determined by the QualifierAlignment style flag
  --sort-includes                - If set, overrides the include sorting behavior
                                   determined by the SortIncludes style flag
  --style=<string>               - Set coding style. <string> can be:
                                   1. A preset: LLVM, GNU, Google, Chromium, Microsoft,
                                      Mozilla, WebKit.
                                   2. 'file' to load style configuration from a
                                      .clang-format file in one of the parent directories
                                      of the source file (for stdin, see --assume-filename).
                                      If no .clang-format file is found, falls back to
                                      --fallback-style.
                                      --style=file is the default.
                                   3. 'file:<format_file_path>' to explicitly specify
                                      the configuration file.
                                   4. "{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 <path-to-this-file>/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. CLion turns it on automatically when there is a .clang-format file under the project root. Code style rules are applied as you type, including indentation, auto-completion, code generation, and refactorings.

clang-format can also be enabled without a .clang-format file. In this case, CLion prompts you to create one based on the current IDE settings or the default LLVM style.

Visual Studio Integration

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

Visual Studio Code Integration

Get the latest Visual Studio Code extension from the Visual Studio Marketplace. The default key-binding is Alt-Shift-F.

Git integration

The script clang/tools/clang-format/git-clang-format can be used to format just the lines touched in git commits:

% git clang-format -h
usage: git clang-format [OPTIONS] [<commit>] [<commit>|--staged] [--] [<file>...]

If zero or one commits are given, run clang-format on all lines that differ
between the working directory and <commit>, which defaults to HEAD.  Changes are
only applied to the working directory, or in the stage/index.

Examples:
  To format staged changes, i.e everything that's been `git add`ed:
    git clang-format

  To also format everything touched in the most recent commit:
    git clang-format HEAD~1

  If you're on a branch off main, to format everything touched on your branch:
    git clang-format main

If two commits are given (requires --diff), run clang-format on all lines in the
second <commit> that differ from the first <commit>.

The following git-config settings set the default of the corresponding option:
  clangFormat.binary
  clangFormat.commit
  clangFormat.extensions
  clangFormat.style

positional arguments:
  <commit>              revision from which to compute the diff
  <file>...             if specified, only consider differences in these files

optional arguments:
  -h, --help            show this help message and exit
  --binary BINARY       path to clang-format
  --commit COMMIT       default commit to use if none is specified
  --diff                print a diff instead of applying the changes
  --diffstat            print a diffstat instead of applying the changes
  --extensions EXTENSIONS
                        comma-separated list of file extensions to format, excluding the period and case-insensitive
  -f, --force           allow changes to unstaged files
  -p, --patch           select hunks interactively
  -q, --quiet           print less information
  --staged, --cached    format lines in the stage instead of the working dir
  --style STYLE         passed to clang-format
  -v, --verbose         print extra information

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] [-iregex PATTERN] [-sort-includes] [-v] [-style STYLE]
                            [-fallback-style FALLBACK_STYLE] [-binary BINARY]

This script reads input from a unified diff and reformats all the changed
lines. This is useful to reformat all the lines touched by a specific patch.
Example usage for git/svn users:

  git diff -U0 --no-color --relative HEAD^ | clang-format-diff.py -p1 -i
  svn diff --diff-cmd=diff -x-U0 | clang-format-diff.py -i

It should be noted that the filename contained in the diff is used unmodified
to determine the source file to update. Users calling this script directly
should be careful to ensure that the path in the diff is correct relative to the
current working directory.

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 (case sensitive, overrides -iregex)
  -iregex PATTERN       custom pattern selecting file paths to reformat (case insensitive, overridden by -regex)
  -sort-includes        let clang-format sort include blocks
  -v, --verbose         be more verbose, ineffective without -i
  -style STYLE          formatting style to apply (LLVM, GNU, Google, Chromium, Microsoft, Mozilla, WebKit)
  -fallback-style FALLBACK_STYLE
                        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-formatfile to use.
  -binary BINARY        location of binary to use for clang-format

To reformat all the lines in the latest Mercurial/hg commit, do:

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

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

These commands use the file paths shown in the diff output so they will only work from the root of the repository.

Current State of Clang Format for LLVM

The following table Clang Formatted Status shows the current status of clang-formatting for the entire LLVM source tree.