C / C++ / Objective-C Formatter

clang-format in the browser

clang-format is the formatter from the LLVM project, the same tool behind format-on-save in CLion, VS Code’s C/C++ extension and most C++ code review bots. Normally it reads a .clang-format file from your repository. Here you pick the pieces that matter from the options panel instead, and the formatter runs inside the page, so firmware, game engine code or anything under NDA is not sent to a server.

Input that has #include lines is detected automatically, as are Objective-C @interface and @implementation blocks. Press Ctrl/Cmd+Enter to format, or let it update as you type.

Language and Style

Language tells clang-format how to read the code: C++, C or Objective-C. In practice C and C++ come out nearly the same, because clang-format parses both with its C++ rules. Objective-C matters more, since method declarations like - (void)reload:(BOOL)animated need their own handling. With C++ selected, input containing @interface, @implementation, @protocol or #import is switched to Objective-C for you.

Style picks a predefined base style, matching BasedOnStyle in a .clang-format file:

• LLVM (default): attached braces, char **argv and const Item &item with the symbol next to the name, access specifiers flush with the class.
• Google and Chromium: attached braces, char** argv with the symbol on the type, and public: indented by one space. Google also regroups includes into C headers, C++ standard headers and project headers.
• Mozilla: class and function braces on their own lines, control-statement braces attached. WebKit is similar but keeps the class brace attached.
• Microsoft: every brace on its own line, namespaces included (Allman style).
• GNU: return types on a separate line, a space before every argument list as in main (void), and braces of if and for indented half a level.

LLVM, Google, Chromium and Microsoft also append a // namespace shop comment to the brace that closes a namespace.

Two values always come from the toolbar rather than the style: indentation width (or tabs, via Indent) and an 80-column limit. That differs from some styles’ defaults, such as Microsoft’s 120 columns or WebKit’s unlimited line length.

Include sorting and protected regions

clang-format sorts each block of #include lines alphabetically, where a block is a run of lines without a blank line in between. That is usually harmless, but some headers depend on being included first: <windows.h> before <shellapi.h> is the classic case. Separate order-sensitive includes with a blank line, or protect them with // clang-format off and // clang-format on; the lines between those comments are left exactly as written. The same comments help with hand-aligned lookup tables and register maps.

A formatter, not a compiler

clang-format works from tokens and does not need the code to compile. Missing headers, undefined types and even unbalanced braces do not produce an error message. That is useful for fragments, but it means a clean format is not proof the code is valid. A missing closing brace shows up indirectly: everything after it is indented one level deeper than you expect, and the file ends without returning to column 1.

Examples

#include <vector>
#include "inventory/item.h"
#include <stdio.h>
#include <string>
namespace shop{class Cart{public:void add(const Item&item){items_.push_back(item);}
double total()const{double t=0;for(const auto&i:items_)t+=i.price*i.qty;return t;}
private:std::vector<Item> items_;};}

#include <stdio.h>

#include <string>
#include <vector>

#include "inventory/item.h"
namespace shop {
class Cart {
 public:
  void add(const Item& item) { items_.push_back(item); }
  double total() const {
    double t = 0;
    for (const auto& i : items_) t += i.price * i.qty;
    return t;
  }

 private:
  std::vector<Item> items_;
};
}  // namespace shop

#include <stdint.h>
typedef struct{uint16_t raw;float celsius;}reading_t;
static float to_celsius(uint16_t raw){return (raw*0.0625f)-40.0f;}
int read_sensor(reading_t*out){if(!out)return -1;out->raw=adc_read(3);out->celsius=to_celsius(out->raw);return 0;}

#include <stdint.h>
typedef struct
{
  uint16_t raw;
  float celsius;
} reading_t;
static float
to_celsius (uint16_t raw)
{
  return (raw * 0.0625f) - 40.0f;
}
int
read_sensor (reading_t *out)
{
  if (!out)
    return -1;
  out->raw = adc_read (3);
  out->celsius = to_celsius (out->raw);
  return 0;
}

#import <UIKit/UIKit.h>
@interface OrderView:UIView
@property(nonatomic,strong) NSString *title;
@property(nonatomic,copy) void(^onSelect)(NSString *orderId);
-(void)reloadWithOrders:(NSArray<Order*>*)orders animated:(BOOL)animated;
@end

#import <UIKit/UIKit.h>
@interface OrderView : UIView
@property(nonatomic, strong) NSString *title;
@property(nonatomic, copy) void (^onSelect)(NSString *orderId);
- (void)reloadWithOrders:(NSArray<Order *> *)orders animated:(BOOL)animated;
@end

Common errors and how to fix them

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