C Beautifier & Formatter

Pick the brace style your project already uses

Match the repository even when you dislike its choice. A reformat spread across a file buries the real diff and makes git blame useless for that region, which costs more than the layout ever gains. For a project with no history yet, K&R at 4 spaces is the safest starting point.

The kernel case is worth knowing about. Its 8 column tabs look like an accident and are not. The kernel style document treats deep nesting as a design warning, so it makes each level expensive on purpose: run out of screen width and the function needs splitting. Set Indent to Tab with K&R braces to see what a patch has to look like before that project takes it.

What the Format button changes

Every line is rebuilt, not patched. Your source runs through a small C tokenizer first, so strings, character constants, comments and preprocessor lines are set aside before any spacing rule touches the code. That is what stops a brace inside a string literal from throwing off the indentation.

• Indentation comes from brace depth at the width you pick. Old tabs and mixed leading whitespace are replaced outright.
• Semicolons outside a for header break the line, so you get one statement per line.
• Spacing follows normal C convention: around binary operators, none inside parentheses, none between a function name and its argument list, one space after if, for, while and switch.
• Prefix and postfix operators stay glued to their operand, so *p, &x, -1 and i++ survive instead of turning into arithmetic.
• Pointers normalize to char *p. The star binds to the declarator, not the type, and char* a, b; declares one pointer and one plain char. Right alignment keeps that visible.
• Casts lose the gap before their value, and case labels indent under switch.
• Trailing whitespace goes, runs of blank lines collapse to one, and goto labels outdent a level.

Output replaces your input in the same box. CtrlZ brings the original back if you want to compare.

The macro that breaks your indentation

Directives take a separate path. They sit at column 0 so #ifdef ladders stay readable inside a nested function, whitespace between # and the directive name is removed, and backslash continuation lines get one level of indent under their directive. The body of a #define is left exactly as written, spacing included, because macro text is substituted verbatim and reformatting it risks changing what the compiler sees.

One pattern defeats all of that. A macro holding half a brace pair, the classic #define BEGIN {, breaks the depth counter for every line after it. The status bar reports the mismatch rather than guessing, and indentation past that point is unreliable. If you see a brace warning on code that compiles fine, a macro is almost always the reason.

Where this stops short

• Long lines are never wrapped. There is no column limit, so a 300 character condition stays 300 characters wide.
• Array and struct initializers keep the line breaks you wrote. A lookup table on one line stays on one line.
• #include lines are neither sorted nor grouped.
• Pointer detection is a heuristic built on type keywords and the _t suffix. A typedef named Matrix in Matrix * m; reads as multiplication and gets spaced that way.
• C++ files mostly survive, but classes, templates, namespaces and access labels are not handled. Use the C++ beautifier for those.
• Files past roughly 2 MB are refused rather than freezing the tab.

The output will not match clang-format line for line, and it is not meant to. This page is for reading code someone pasted at you. What lands in a commit should go through the config your repository already carries.

The same job in your editor

Three tools cover almost every C codebase and all of them run offline in a pre-commit hook.

Commit the settings so the layout stops being a personal preference:

GNU indent ships with most distributions and predates clang by decades. It handles plain C fine through -kr, -gnu and -orig, though it has no idea what to do with newer attributes.