indent

Additional Notes

indent reformats C and C++ source code according to configurable indentation and formatting rules. It adjusts indentation, line breaks, spacing, brace placement, comment formatting, and other code layout aspects to match a specified style.

It supports several built-in coding styles (Kernighan & Ritchie, GNU, Berkeley, Linux kernel) and allows fine-grained control over virtually every formatting detail through command-line options. It is useful for enforcing consistent code style across a project, cleaning up poorly formatted code, or batch-formatting many files at once.

Syntax

indent [options] file...

Parameters

• file: One or more C or C++ source files to format. Files are modified in place unless backup options are specified.

Common Style Options

• -kr: Use Kernighan & Ritchie style.
• -gnu: Use GNU style (default).
• -orig: Use Berkeley style.
• -linux: Use Linux kernel style.
• -bap: Blank line after procedure bodies.
• -bad: Blank line after declarations.
• -bap: Blank line after function bodies.
• -bbb: Blank line before block comments.
• -nbad: Do not force blank lines after declarations.
• -bbo: Prefer break before boolean operators.
• -bc: Put else on new line after closing brace.
• -bl: Put opening braces on new lines.
• -bli n: Indent braces by n spaces.
• -bls: Put braces of struct/union/enum on new lines.
• -br: Put opening braces on the same line as the statement.
• -bs: Prefer a space between sizeof and its argument.
• -c n: Comment indentation column.
• -cd n: Declaration comment column.
• -cdb: Comment delimiters on blank lines.
• -ce: Cuddle else with preceding }.
• -ci n: Continuation indent of n spaces.
• -cli n: Case label indent of n spaces.
• -d n: Set indentation for comments not to the right of code.
• -di n: Put variables in columns.
• -fc1: Format comments in first column.
• -fca: Format all comments.
• -hnl: Prefer to break long lines at newlines.
• -i n: Set indentation level to n spaces (default is 2).
• -ip n: Indent parameter types in old-style function definitions by n spaces.
• -l n: Set maximum line length to n columns (default is 78).
• -lc n: Set maximum comment line length.
• -lp: Align continued line parameter lists.
• -npsl: Put return type on the same line as function name.
• -psl: Put return type on its own line before function name.
• -sc: Put */ at the right of comments.
• -sob: Swallow optional blank lines.
• -st: Write output to stdout instead of modifying files in place.
• -T typename: Add typename to the type recognition list.
• -ts n: Set tab size to n columns.
• -ut: Use tabs for indentation.
• -nut: Use spaces for indentation (no tabs).
• -v: Verbose mode.

Examples

indent -kr file.c

Format file.c in Kernighan & Ritchie style.

indent -linux -i8 file.c

Format using Linux kernel style with 8-space indentation.

indent -st -br -ce file.c > formatted.c

Format file.c with braces on the same line and else cuddled, writing to stdout.

indent -gnu -l120 -nut *.c

Format all C files in the current directory with GNU style, 120-character line length, and spaces instead of tabs.

indent -kr -bad -bap -i4 -br -ce -nut source.c

Apply a custom style based on K&R but with 4-space indentation and no tabs.

Practical Notes

• indent modifies files in place by default. Use -st to send output to stdout and inspect changes first.
• Always back up your source files (-b flag creates a backup with ~ suffix) before batch-formatting.
• Not all code formats perfectly; indent may struggle with preprocessor macros, #ifdef blocks, or unusual constructs.
• For large projects, use indent with version control (e.g., git diff afterward) to review all changes.
• indent only handles C and C++. For other languages, use language-specific formatters.
• The tool is most useful when applied consistently to an entire codebase.